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  1. #1
    Andy Jarchow's Avatar
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    Default Why is a three pronged receptacle unsafe?

    Hello all,

    In this profession it is easier to find out what is right and wrong than why something is wrong. Three prong receptacles without a ground are safety hazards. Why?

    If it is a two pronged receptacle it's ok… I have some ideas but would like to learn as much as I can. I know if I’m asking why I’m sure my client maybe wondering the same.

    Thank you

    Have a great day!

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  2. #2
    Nolan Kienitz's Avatar
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    Default Re: Why is a three pronged receptacle unsafe?

    Because there is "no ground".

    The 3-slot** receptacle provides a presentation that there "is" a ground and in fact it is not there.

    That above statement is predicated upon an old 2-wire system that used to have 2-wire receptacles and the receptacles were replaced with 3-wire receptacles and no effort was made to establish a ground.

    It will work, but the representation of what is there and what is not there is misleading and thus not safe.

    JP will be providing more detailed information with code references as well before long.


    **Thanks for jogging my gray matter Darren

    Last edited by Nolan Kienitz; 03-04-2010 at 06:12 AM.

  3. #3
    Roger Frazee's Avatar
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    Default Re: Why is a three pronged receptacle unsafe?

    I'm sure there will be several different replies to your question. When you install a 3 prong grounding type receptacle to a branch circuit without equipment ground... your essentially telling people that the circuit has an equipment ground when it really does not. Meaning that if an appliance or other equipment is plugged into the outlet and that appliance has a 3 prong plug then it also has metal that is capable of being touched by people when they use it. The ground wire in the power cord is connected to that appliance metal. If a fault occurs to the metal the fault circuit is completed via the power cord ground wire (green) and the equipment ground wire in the branch circuit. This will cause the circuit breaker to trip on overcurrent ... there by saving you from possible electrocution.

    In contrast if the proper two prong receptacle is installed then a 3 prong power cord from an appliance that requires the equipment ground in the branch circuit for human safety cannot be plugged into that receptacle.

    I drew this diagram (attached below) a few years ago to show the fault path for a hot wire in a branch circuit contacting a metal receptacle box. So consider an appliance with a 3 prong power cord plugged into the receptacle shown. A hot wire in the appliance comes loose and touches the metal case of the appliance. The fault current transfers to the power cord ground wire which is attached to that metal case. The fault current then travels to the receptacle where it is connected to the equipment ground wire. The equipment ground wire carries the current to the panel .. then the fault current travels to the utility transformer center tap. This completes a low impedance fault circuit that allows enough current to flow through your 15 or 20 amp circuit breaker to trip it and clears the fault so you never get electrocuted.

    Now picture the equipment ground not being there because you installed a 3 prong receptacle in place of a 2 prong receptacle. Remember the equipment ground does not exist. You plug in a faulty appliance and the hot wire at some point touches the metal case of that appliance. Since there is no equipment ground to complete the fault circuit the metal of the appliance comes to line voltage and a breaker will never trip. You touch the appliance and ..zap.. you get shocked or worse. So if you have 2 prong receptacles and no equipment ground never install 3 prong receptacles unless they are gfci ones or gfci protected..

    If it is a two pronged receptacle it's ok…
    It's ok because it tells you what you have ... no equipment ground... but it is not as safe as a branch circuit that has the equipment ground. Note that 2 prong receptacles installed on ungrounded systems do not facilitate protection from ground fault to an appliance metal case. You will get shocked in the event of a hot wire fault to the appliance metal. Which is why grounded systems are now the norm....improved human safety.

    However in todays' world most appliances that are equipped with power cords that are two prong are double insulated which makes it very unlikely that a hot wire will ever contact the metal case of the appliance. Many are plastic or composite cased and double insulated. So let the plug on the appliance and the appliance listing be your safety guide. And don't use those funky adapters that allow 3 prong cords to plug into a 2 prong receptacles. If you do this make sure you use a gfci protective device that plugs into the adapter and you plug the appliance or tool into the gfci.




    Last edited by Roger Frazee; 03-04-2010 at 10:48 PM. Reason: correcting spelling

  4. #4
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    Default Re: Why is a three pronged receptacle unsafe?

    Quote Originally Posted by Mike Krueger View Post
    Hello all,

    In this profession it is easier to find out what is right and wrong than why something is wrong. Three prong receptacles without a ground are safety hazards. Why?

    If it is a two pronged receptacle it's ok… I have some ideas but would like to learn as much as I can. I know if I’m asking why I’m sure my client maybe wondering the same.

    Thank you

    Have a great day!
    Such receptacles, if present, are required to be protected via a Ground Fault Circuit Interupter, and individually labeled "No Equipment Ground".

    Two types of GFCIs - those that are designed to protect "personnel" and those that are designed to protect "equipment" (different tolerances for inbalanced levels/objectional current and trip time).

    In past versions of the NEC combination GFCI/receptacles were not allowed to protect downstream receptacles or outlets if there was no equipment ground conductor, this is no longer the case with more recent editions of the NEC.

    The GFCI device doesn't substitute for an egc but is thought to mitigate the lack of one as an alternate (to the circuit breaker) means to open the circuit. The GFCI serves to protect in some part injury to persons, where as the CB serves in part to protect damage to the electrical system.

    GFCIs do not require an equipment ground to determine an inbalance and trip (open). GFCI Circuit Breakers and GFCI receptacles (when installed correctly) open the hot when they trip. Portable GFCI devices such open both the Hot and the "neutral" (grounded conductor) when they trip, an added, and often essential protection (to persons) when working electricity in environments where multiwire branch circuits, wiring errors, etc. may be present (such as construction/temporary wiring or older installations with unknown/untested multi-generational adaptations are present).

    Remember also that EGC may be other than a wire conductor, ex. ribbon, bonded metalic conduit, etc., and in older flexible metalic conduit and cable may be undersized or not sufficient (but your tester may still show "grounded". Also remember that in decades past intermittant connections to water pipes, etc. beyond the service entrance were common place.

    Another often overlooked occurance in older homes is the presence of conductive/metalic face plates for switches and receptacles which are not bonded.

    Finally, regarding "two prong" receptacles, non-restrictive older two-prong receptacles which allow a polarized (one side wider blade) plug to be inserted in both directions; and the use of portable electric equipment, such as portable lamps, with older non-polarized cord caps (plugs) can present dangers of their own (ex. non-polarized cord cap on portable lamp can allow to be plugged in reverse - thus electrifying the shell of the lampp holder - and subjecting the user to dangerous objectional current should the user change the lamp (bulb) while the device is plugged in and make contact or arc, as well as when the integral switch is operated it opens and closes the grounded conductor not the hot. Similar "hazards" might be encountered with older ventillation fans which the "fan unit" is not hardwired but has a non-polarized cord cap, is removable from its mounts and is plugged into the integral receptacle within the shell. Older combination light fixtures, medicine cabinets, etc. which incorporated a convenience receptacle/shaver outlet often contained a non-grounded, and non-polarized receptacle - notably usually located just above or adjacent to a bathroom or kitchen sink, and oftentimes are wired not via a wall switch but having a metal switch on the light fixture/metalic bathroom cabinet itself.

    HTH.

    Last edited by H.G. Watson, Sr.; 03-03-2010 at 12:18 PM.

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    Default Re: Why is a three pronged receptacle unsafe?

    I've been doing HI's for 14 years now. During that time I have never, ever seen an ungrounded 3-prong receptacle.

    Most what I see are "3-SLOT' ungrounded receptacles.

    I'm sure there are 3-prong ungrounded receptacles out there (can someone post a photo?).

    The phase 'sub-panel' bugs Jerry; "3-prong receptacle" bugs me.

    Darren www.aboutthehouseinspections.com
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  6. #6
    Andy Jarchow's Avatar
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    Default Re: Why is a three pronged receptacle unsafe?

    Wow great stuff. Thank you for taking so much time in answering my questions. I understand why now! I knew the three slotted receptacle gave the assumption that an equipment ground was present but didn’t totally understand how it worked. My guess is most people don’t understand this. They replace the old two slotted receptacles with three or they buy adaptors and plug those in.

    Thanks again everyone!


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    Default Re: Why is a three pronged receptacle unsafe?

    Darren
    Much like "Trash", "Cigarette",phone", or "Cable TV" receptacle. They describe what each is designed to receive. In the same way a "3 Prong Receptacle" is designed to receive "3 Prongs".
    The "3 Slot" receptacles I see are are most often used for a stove or dryer.

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  8. #8
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    Thumbs up Re: Why is a three pronged receptacle unsafe?

    Rick,

    Wow a low voltage phone wire did that?
    PS thank you for the defense on the prong/slot thing…


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    Default Re: Why is a three pronged receptacle unsafe?

    "Wow a low voltage phone wire did that? "

    I only done a google image search on "phone receptacle", and found this one.
    But, no, I do not think that telephone line voltage done that.
    Simply not enough current.
    I suspect, lighting, miswired to a higher voltage, or something else, it looks like its next to a fire place could be a crack in the wall behind it.



    ' correct a wise man and you gain a friend... correct a fool and he'll bloody your nose'.

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    Default Re: Why is a three pronged receptacle unsafe?

    Quote Originally Posted by Rick Cantrell View Post
    "Wow a low voltage phone wire did that? "

    I only done a google image search on "phone receptacle", and found this one.
    But, no, I do not think that telephone line voltage done that.
    Simply not enough current.
    I suspect, lighting, miswired to a higher voltage, or something else, it looks like its next to a fire place could be a crack in the wall behind it.
    Back in the day when Western Electric's first "Princess Style" phones first came out dial and hang-up button on the handset, lighted rotary dial, had modern style "plug" as opposed to the old four prong cord, and coiled cord between handset and base was hardwired, the Telecoms weren't delivering enough current to light the dial and operate the early adjustable volume and ring; Telecoms would install a transformer to boost the tel line voltage on the inside of the home (plugging into a wall receptacle with a two-prong non-polarized cord/plug set) and feed current to a brass distribution bar - subsequent "extensions" were wired off of it. Long since telecoms have boosted the current and reduced losses on the distribution. You might be surprised how many older homes still have these transformers, hidden in the rafters, floor joists, ceilings of subsequently finished basements, actively plugged in and connected electrically to the telephone distribution. These same old princess phones will work on today's system without the transformer/rectifier plugged in or present. However I have seen more than one fire caused or the start of a fire abetted by their presence.

    If encountered they (transformer) should be removed.

    Lightening strikes can also transmit via hard wired land-line phones - hence the precaution to not use during electrical storm activity.


  11. #11
    Roger Frazee's Avatar
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    Default Re: Why is a three pronged receptacle unsafe?

    Quote Originally Posted by Darren Miller View Post
    I've been doing HI's for 14 years now. During that time I have never, ever seen an ungrounded 3-prong receptacle.

    Most what I see are "3-SLOT' ungrounded receptacles.

    I'm sure there are 3-prong ungrounded receptacles out there (can someone post a photo?).

    The phase 'sub-panel' bugs Jerry; "3-prong receptacle" bugs me.

    A 3 prong dryer receptacle comes to mind ... I assume here your talking about a ' 3 prong' receptacle that is not a 'grounding type' receptacle.


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    Default Re: Why is a three pronged receptacle unsafe?

    I took (okay AssUMed) the OP to mean a 125V 15 amp face grounding type duplex receptacle vs. either a 125V 15 amp face grounding type duplex receptacle with open or missing, floating, or insufficient ground, OR vs. a 125V 15 or 20 amp face non-grounding type duplex receptacle.

    Be it described as one that recieves three "prong", "blade" cap or has three "slots" as compared to a 125V 1-PH non-grounding type receptacle, be it polarized or not, that receives two "prong", "blade" cap or has two "slots".

    I did not consider a three-slot/receiving three "prongs", "blade" cap, 250V receptacle - since don't consider a two "prong", "blade", "slot" version (but a four-wire/prong/blade/slot) which is grounded. If the OP is questioning the newer requirements for four-wire range, electric dryer, and similar 120/240 circuits that were previously wired without egc as three wire circuits, that's a slightly different subject.

    A receptacle which receives three prongs/blades receives as in receptacle. Doesn't bother me.

    Old NEC editions actually used the phrase sub-panel with feeder supplied panelboards, it also referred to those "feeders" as "sub-feeders". I provided one or more references sometime back on an old post, now more correctly refers to as remote panelboard in discussing feeder supplied panelboards.

    I don't get that hung up on what was for 50 years common technical language having been rewritten/defined by later editions of the NEC.

    What does bug me is referring to a receptacle as an outlet and expecting everyone to understand that you mean specifically a receptacle, excluding any other type of "outlet", or you mean it to refer to a duplex receptacle (which is actually two receptacles).

    Last edited by H.G. Watson, Sr.; 03-04-2010 at 10:29 AM.

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    Cool Re: Why is a three pronged receptacle unsafe?

    All great posts. But I think Roger Frazee went above and beyond,
    great post Roger.


  14. #14
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    Thumbs up Re: Why is a three pronged receptacle unsafe?

    I agree Robert.

    I learned more on this site in a couple days than I did taking a 6 month course...
    mk


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    Default Re: Why is a three pronged receptacle unsafe?

    Quote Originally Posted by Darren Miller View Post
    I've been doing HI's for 14 years now. During that time I have never, ever seen an ungrounded 3-prong receptacle.
    To my knowledge, they do not make such an animal as that would be referred to as a "plug", not a "receptacle" as a "receptacle" is something you put something in (i.e., the plug "goes into" the receptacle).

    Most what I see are "3-SLOT' ungrounded receptacles.
    Hopefully you never seen anything else.

    I'm sure there are 3-prong ungrounded receptacles out there (can someone post a photo?).
    I doubt it, see my comment above.

    The phase 'sub-panel' bugs Jerry; "3-prong receptacle" bugs me.
    Bugs me too, and in fact, I tried to get everyone here to use the terms '2-wire' and '3-wire' (or 'non-grounding type' and 'grounding type') but eventually put that on the back burner until after the submarine panel things is understood - and there are still frequent posts about people not understanding where the neutral is bonded to ground and those posts almost always contain the submarine panel reference and only understand (or appear to understand) when thinking 'service equipment' and 'not service equipment' panels.

    Oh, well, I am on your side, but I've already fought that battle years ago and put it on the back burner.

    Jerry Peck, Construction / Litigation Consultant
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    Default Re: Why is a three pronged receptacle unsafe?

    "I tried to get everyone here to use the terms '2-wire' and '3-wire' "

    I don't recall that, but I do like that description better than 2-3 prong.

    ' correct a wise man and you gain a friend... correct a fool and he'll bloody your nose'.

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    Default Re: Why is a three pronged receptacle unsafe?

    Quote Originally Posted by Rick Cantrell View Post
    "I tried to get everyone here to use the terms '2-wire' and '3-wire' "

    I don't recall that, but I do like that description better than 2-3 prong.
    Except that ground (ecg) can be provided by other than a wire for a conductor. This confuses the "issue" when ground is provided via grounded metalic conduit or cable assembly which incorporates other than a "wire" for ground; further complicated by the fact that most schematics/plans presume ground and do not include it in diagrams. Self-grounding switches, receptacles, etc. are still produced and sold even today, metalic boxes, as well.


  18. #18
    Roger Frazee's Avatar
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    Default Re: Why is a three pronged receptacle unsafe?

    I certainly agree but I didn't feel like disrupting the thread fighting that technical discrepancy until the question asked had been answered satisfactory for MK .... I knew someone likely would be along to make the point of 2 prong to 3 prong and 2 wire to 3 wire grounding type receptacles and plugs.

    but to further help out to those ends I'll post a nema straight blade chart link so the differences can be reviewed by those interested...


    Nema Straight Blade Chart

    And this page has some very good education and electrical info. You might enjoy navigating the Siemens link under on line education and others.

    Resources

    And this link is very useful

    Industry Tables

    Last edited by Roger Frazee; 03-04-2010 at 08:39 PM.

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    Default Re: Why is a three pronged receptacle unsafe?

    Quote Originally Posted by James Risley View Post
    THERE WAS RECALL EITHER TO REPLACE OR REMOVE THESE TRANSFORMERS MANY YEARS AGO DUE TO FIRE ISSUES.

    Really?!? Point me to it will you? Just what was the date of this "recall"? Pre- or Post-breakup of "The Telephone Company"?

    IIRC there were hundreds of thousands still in use (phones and even more transformers in place) throughout the AT&T break-up by Judge Albert Green and the conversion from "leased equipment" to "customer owned equipment" that followed via the "baby bells". As a former "utility" I don't recall any sort of CPSC "recall" not that they would have had jurisdiction in that brief period (since initially they were all utility owned equipment - pre-break-up).

    Obviously I missed the "memo" please do post the details. (Also please avoid shouting).


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    Default Re: Why is a three pronged receptacle unsafe?

    Well Watson, I guess you just weren't special enough to get your own personal notification.

    Here's a copy of one of the involved documents. This is a Bell System Practice document and is available on line for those capable of using internet searches. Issued November 1979.

    This was pretty common knowledge in "the industry" at the time.

    Attached Files Attached Files

  21. #21
    Tim Spanos's Avatar
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    Default Re: Why is a three pronged receptacle unsafe?

    A three prong (slot) receptacle without a grounding path does not provide protection to the equipment you plug into it...thus anything you plug into it may become energized and shock/electrocute someone.....if it was grounded that means you have a low resistance ground fault current path ( basicly a good solid connection back to the breaker box ) that will cause the fuse to blow or breaker to trip when a fault occures on the equipment you have pluged into it.....These receptacles are reffered to as grounding type receptacles.....the 2 slot receptacle is called a non grounding type receptacle...and does not provide a pathway to blow fuse or trip breaker....they say it is safer because newer equipment that requires a grounding path will be equiped with three prongs and you cant plug it into a non grounding type receptacle outlet...only equpment that does not require a grounding path may be plugged into it.....


  22. #22
    Roger Frazee's Avatar
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    Default Re: Why is a three pronged receptacle unsafe?

    Quote Originally Posted by Mike Krueger View Post
    Wow great stuff. Thank you for taking so much time in answering my questions. I understand why now! I knew the three slotted receptacle gave the assumption that an equipment ground was present but didn’t totally understand how it worked. My guess is most people don’t understand this. They replace the old two slotted receptacles with three or they buy adaptors and plug those in.

    Thanks again everyone!
    Mike

    I was just reading the thread again and thought from the question you asked that you may be interested in what we call (slang term) .. a bootleg ground. So let me post a picture of this being done at a receptacle. The picture came from this forum. This very misunderstood trick is done by homeowners or handy men to three wire grounding type receptacles when they are used as replacements for 2 wire non grounding type receptacles. As the picture shows a jumper wire is placed from the neutral screw of the receptacle to the ground screw of the receptacle.

    They are doing this for a couple reasons ... 1.) They want to try to trick a home inspector into thinking the circuit has an equipment ground when he uses his receptacle tester on the outlet or 2.) They think that by doing this they have magically created an equipment ground by using the neutral or grounded leg of the branch circuit.

    Are you aware of the hazard in doing this? If not please ask and some one here can detail why this is a very stupid thing to do. This is something every HI and homeowner for that matter should understand and also how to determine if this has been done.

    Anyway here is a picture of a 3 wire grounding type duplex receptacle that has a bootleg ground and then installed on a 2 wire branch circuit .In my most recent encounter with this the homeowner used cheap speaker wire for the jumper....

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    Last edited by Roger Frazee; 03-06-2010 at 03:40 PM.

  23. #23
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    Default Re: Why is a three pronged receptacle unsafe?

    Quote Originally Posted by Roger Frazee View Post
    Mike

    I was just reading the thread again and thought from the question you asked that you may be interested in what we call (slang term) .. a bootleg ground. So let me post a picture of this being done at a receptacle. The picture came from this forum. This very misunderstood trick is done by homeowners or handy men to three wire grounding type receptacles when they are used as replacements for 2 wire non grounding type receptacles. As the picture shows a jumper wire is placed from the neutral screw of the receptacle to the ground screw of the receptacle.

    They are doing this for a couple reasons ... 1.) They want to try to trick a home inspector into thinking the circuit has an equipment ground when he uses his receptacle tester on the outlet or 2.) They think that by doing this they have magically created an equipment ground by using the neutral or grounded leg of the branch circuit.

    Are you aware of the hazard in doing this? If not please ask and some one here can detail why this is a very stupid thing to do. This is something every HI and homeowner for that matter should understand and also how to determine if this has been done.

    Anyway here is a picture of a 3 wire grounding type duplex receptacle that has a bootleg ground and then installed on a 2 wire branch circuit .In my most recent encounter with this the homeowner used cheap speaker wire for the jumper....
    Thank you Roger,

    No I never heard of a bootleg ground.

    If the tester indicates everything is ok how do you know? Do you take face plates off on older homes and physically check a few?

    No I’m not sure what danger this would cause.

    Thank you for the info!


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    Default Re: Why is a three pronged receptacle unsafe?

    Quote Originally Posted by Bill Kriegh View Post
    Well Watson, I guess you just weren't special enough to get your own personal notification.

    Here's a copy of one of the involved documents. This is a Bell System Practice document and is available on line for those capable of using internet searches. Issued November 1979.

    This was pretty common knowledge in "the industry" at the time.
    Apparently so "uncommon" that one as "common" as you, can't comprehend just what the document you provided, or what is highlighted, even says (because it doesn't say what you characterized it to say, nor does it support your claims or sarcasm!).

    It seems we have a FAILURE TO COMMUNICATE


    I gave example specifically to the PRINCESS type (a.k.a. Western Electric TRIMLINE) type phones, with lighted ROTARY DIAL, volume & ring control on the HANDSET circa 1965-1970. Both phones required transformer - only the TRIMLINE could RING without an external ringer.



    You provided highlights regarding the mandated replacement of transformer KS-20426LD (MD) for centralized power supply mounted in a 2-wire receptacle which powered up to five dial light telephone sets (Note 2) ONLY WHEN SAID TRANSFORMER WAS MANUFACTURED BY AULT, and to REPLACE with one of the SAME NUMBER by ANY OF THE OTHER MANUFACTURERS!!!!! (Which, by the way doesn't support YOUR ASSERTION one BIT. Read up a few lines on your table and you'll find it.)

    Since your supplied document began at and the paragraphs regarding WHAT I REFERRED TO according to YOUR table was paragraph numbers 2.03-2.07......I still see NO EVIDENCE of a "RECALL for the subject phones I discussed (because of course there wasn't one). They simply became redundant and unnecessary, but for that "leased equipment" which was converted/abandonded to become "customer owned equipment" NO SUCH RECALL/REMOVAL initiated by "The Phone Company" took place. Many, many years later, the "baby bells" instructed Repair to remove when encountered, and for those customers who did not have inside wire maintence plans and the "visit" was on "their dime", no discount for time charged was passed along for the time involved in the removal/rewire, thus several winning class action suits for credits to customers of "the phone company" regarding that practice - and several winning cases regarding claims for damages and injuries due to the presence of said equipment, which were reviewed by the court of Judge Green (but a limit of liability and time was imposed long ago upon the "baby bells" which has long since passed).

    Neither 2012A's nor their sucessor 2012C's were EVER recalled! Neither were the majority of the other than AULT xfmrs, and few AULTs were ever in the field.

    I read note 2 instructions to NOT use a specific AULT manufactured transformer and to use same transformer number manufactured by any other supplier for lighting FIVE OR MORE lighted dial phones.

    Both the "PRINCESS" ("TRIMLINE" by Western Electric) telephone sets, and their respective (and by then unnecessary transformers) were "converted" to customer owned equipment with the First pre-bust case stage rumblings of the Bell "Bust-up".

    Still waiting (altough less sarcastically than you, apparently) for "the memo" you claimed exists. Your single page pdf doesn't say what you claim it says. Show me the "recall" (beef). A notice to swap out a transformer specific manufacturer and to replace with an equivalent one doesn't support either your sarcasm or your assertion.

    The 2012A and 2012C transformers (the ones I was speaking of) were NEVER RECALLED. When AT&T was divested of the "bells" they were left in place with transformers for those customers who were charged off after years of leasing. Those previously leased phones which were returned and later sold to consumers were simply sold without transformers and light bulbs for the dial.

    The ENTIRE document you tried to modify to meet your needs, so very unsucessfully, can be viewed here: (CLICKABLE LINK - pdf): http://wedophones.com/TheBellSystem/...6-100-7911.pdf

    You'll find them starting on page 2. Notes are on page 9. You can STILL find these transformers (sometimes with princess/trimline phones in place, often times withOUT any trimline phones (some of the first to use the modern type "jack" mount) in place and the homeowner has no clue either it is there, or its purpose. They should be removed.

    Moo-Moo, Don't tell me what I know, Charlie Brown!

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    Last edited by H.G. Watson, Sr.; 03-06-2010 at 09:55 PM.

  25. #25
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    Default Re: Why is a three pronged receptacle unsafe?

    Hi Mike

    I'm going to make a few drawings to help with this and will post in about an hour.


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    Default Re: Why is a three pronged receptacle unsafe?

    Quote:

    Originally Posted by H.G. Watson, Sr.
    Back in the day when Western Electric's first "Princess Style" phones first came out dial and hang-up button on the handset, lighted rotary dial, had modern style "plug" as opposed to the old four prong cord, and coiled cord between handset and base was hardwired, the Telecoms weren't delivering enough current to light the dial and operate the early adjustable volume and ring; Telecoms would install a transformer to boost the tel line voltage on the inside of the home (plugging into a wall receptacle with a two-prong non-polarized cord/plug set) and feed current to a brass distribution bar - subsequent "extensions" were wired off of it. Long since telecoms have boosted the current and reduced losses on the distribution. You might be surprised how many older homes still have these transformers, hidden in the rafters, floor joists, ceilings of subsequently finished basements, actively plugged in and connected electrically to the telephone distribution. These same old princess phones will work on today's system without the transformer/rectifier plugged in or present. However I have seen more than one fire caused or the start of a fire abetted by their presence.

    If encountered they (transformer) should be removed.

    Lightening strikes can also transmit via hard wired land-line phones - hence the precaution to not use during electrical storm activity.




    THERE WAS RECALL EITHER TO REPLACE OR REMOVE THESE TRANSFORMERS MANY YEARS AGO DUE TO FIRE ISSUES.



    Quote Originally Posted by H.G. Watson, Sr. View Post
    Really?!? Point me to it will you? Just what was the date of this "recall"? Pre- or Post-breakup of "The Telephone Company"?

    IIRC there were hundreds of thousands still in use (phones and even more transformers in place) throughout the AT&T break-up by Judge Albert Green and the conversion from "leased equipment" to "customer owned equipment" that followed via the "baby bells". As a former "utility" I don't recall any sort of CPSC "recall" not that they would have had jurisdiction in that brief period (since initially they were all utility owned equipment - pre-break-up).

    Obviously I missed the "memo" please do post the details. (Also please avoid shouting).

    So where exactly in the above exchange is anything about phones being recalled? I provided an internal Bell System document that indicated that the transformer in question was used for some phone installations and the phone Co. was wanting them changed out. Sure sounds like a recall to me. YOU can (and probably will) call it something else. I know what the phone guys called it. These transformers were typically used in multiple phone homes so additional lighted dial phones wouldn't require a transformer change out or the temptation to install multiple transformers, a no-no for the way phone lines are typically hooked up.

    Of course, you bring up the fact you were refering to specific model transformers after having said you weren't aware of any transformer recalls and info was provided for you about one.

    Maybe if you spent more productive time running your backside between the north and south abodes you have you wouldn't have as much time to ........ Aw heck. I'm not going to explain it to you. It's more fun looking at the bibles you write when all anybody wanted was a yes or no answer. At least the other guy here who does that provides useful information.


  27. #27
    Roger Frazee's Avatar
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    Default Re: Why is a three pronged receptacle unsafe?

    Quote Originally Posted by Mike Krueger View Post
    Thank you Roger,

    No I never heard of a bootleg ground.

    If the tester indicates everything is ok how do you know? Do you take face plates off on older homes and physically check a few?

    No I’m not sure what danger this would cause.

    Thank you for the info!
    Sorry Mike ... it took me a little longer than I was expecting due to the drawings were not to my satisfaction but I think they are good enough to illustrate the improper connection to the grounded leg and ground screw of a receptacle.

    First thing to understand is the difference between the grounded leg (sometimes called the neutral) of a 120 volt branch circuit and the equipment ground wire in that circuit. The grounded leg is a current carrying wire. It has the same current on it that the hot wire has flowing on it. It takes both the hot wire and the grounded leg to complete the circuit with the transformer (source). You can see this in the drawing. Both these wires are part of the energized circuit when you are operating an appliance or other power utilization equipment on the branch circuit.

    In contrast the equipment ground wire is present only for human safety and only carries current when a ground fault has occurred....and then only briefly till the circuit breaker opens. So it is a non current carrying wire of the branch circuit under normal operating conditions.

    Now remember that all current whether it is system current or fault current will take any path made available to it to reach the transformer. So when you connect that receptacle ground screw to the grounded leg of the circuit you have made an alternate path for the current on the grounded leg to use to seek the source. The current will flow on both paths if it can get to the source over those paths. The lower the impedance/resistance to the source the more current that will use the path(s).

    The first drawing is showing a typical 3 wire branch circuit. Just picture the load as some appliance plugged into a 3 wire grounding type receptacle.

    The 2nd drawing is showing a bootleg ground on a 2 wire branch circuit and notice you have 2 paths which have been made available for current to use. One path is normal the other is an unwanted path for current over the bootleg ground. Notice that the current is using the equipment ground of the power cord. Also remember that power cord ground wire connects to the metal case of the appliance that you can touch. This is effectively energizing the metal case of the appliance. This doesn't pose a great danger as such because the alternate path has no low impedance route to the transformer center tap.

    The 3rd diagram is showing where it gets much more dangerous. The grounded leg has opened between the receptacle and the service equipment. Now only one path is available to the current and that is the path over the bootleg ground to the appliance metal. You walk up and turn the appliance on and receive a shock because the appliance has no voltage drop across it (not connected to the center tap of the transformer which is at zero volts) and is energized at the full 120 volts. This is like sticking your finger in a light socket. All you need to do is make a reasonably low impedance path for that current to use to get to the transformer.

    So in the 4th drawing is another way to get shocked ...while you are trying to figure out what is wrong with your appliance you reach over and touch your refrigerator, which is plugged into a 3 wire branch circuit with equipment ground, while at the same time touching the appliance plugged into the receptacle with the ' bootleg ground '. Because the refrigerator metal is connected to the equipment ground of its branch circuit you have just given the alternate path caused by the ' bootleg ' of your appliance connected to the two wire circuit a path to the transformer over the refrigerator equipment ground. You are now in series with a completed circuit and will get shocked or possibly electrocuted as current can now flow through you to get to the source ( transformer).

    Hope this was clear it is not easy for me to explain. Drawings attached below. I'll have to wait till sometime later this afternoon to answer the other questions you have ...need some sleep... Maybe someone will come along and fill in your other inquiries.

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    Last edited by Roger Frazee; 03-07-2010 at 06:32 AM.

  28. #28
    Andy Jarchow's Avatar
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    Default Re: Why is a three pronged receptacle unsafe?

    Wow thank you Roger. I think you missed your calling-you should be a teacher.

    I understand most of your post. One question I have about the third example. What would be the cause of the open neutral?

    This is a question unrelated to my original post but similar topic. If current travels on the hot wire through the appliance and then back on the neutral to the service panel. In the panel this same neutral wire is hooked to the neutral bus bar that ground wires also connect to. Why doesn’t the current flow back on these ground wires to the equipment?

    Thank you for all your trouble!

    mk


  29. #29
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    Default Re: Why is a three pronged receptacle unsafe?

    BK,

    None of the multitude of transformers from your 79 document were recalled. One model of transformer, when subcontracted supplier Ault made them was directed to be replaced with other subcontractor's supplied same model transformer, since the particular Ault subcontracted/supplied ones did not meet the purchase order specifications.

    I was specific in the description of the phone (first with modern style plug, that also required transformer on the line within the customer's home) that I referred to - and indicated that any such transformer SHOULD BE REMOVED.

    There was no RECALL. "The Phone Company" was under FCC jurisdiction and federal court system post 56 decree up and until the anti-trust consent decree and divestiture January 1, 1984.

    You will not find a "recall", because none was ever made.

    When customers were "allowed" to attach their own phones without a penalty being charged by "the phone company", and cover their phone books (late 70s court decree), the anti-trust actions were already "in the courts". The negotiated series of consent decrees divested "the phone company" from responsibility and liability for the transformers abandonded in place in customers homes, and transfered ownership and financial responsiblity of the wiring within the structures to the customers - and put the communications system wiring under local jurisdictions relative to codes for safety and standards and subject the products to the commercial/consumer/competitive/free marketplace for what was sold/installed thereafter but protected "the phone company" and its divested elements from liability and responsibility for what was no longer "company owned" equipment.

    Wasn't a "recall". Your personal attacks don't change that fact. Those few Ault manufacturered transformers of a particular bell item number were replaced when encountered for a specific reason, obviously you don't remember or knew why. Few were ever installed in the first place.

    I referred to ALL such transformers in residences needing to be removed. Despite lack of any recall, just burried language in a consent decree and Bell immunity, which continued to be litigated and monitored for many, many years.

    Show the "beef" for the non-existant recall.


  30. #30
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    Default Re: Why is a three pronged receptacle unsafe?

    Quote Originally Posted by Mike Krueger View Post
    Wow thank you Roger. I think you missed your calling-you should be a teacher.

    I understand most of your post. One question I have about the third example. What would be the cause of the open neutral?

    This is a question unrelated to my original post but similar topic. If current travels on the hot wire through the appliance and then back on the neutral to the service panel. In the panel this same neutral wire is hooked to the neutral bus bar that ground wires also connect to. Why doesn’t the current flow back on these ground wires to the equipment?

    Thank you for all your trouble!

    mk
    He diagramed the "opening" the cause was the bootleg where the receptacle was not connected to the grounded (neutral) conductor of the circuit but instead to the bootleg groundING jumper. The insertion of a three-pronged cord cap diagramed to the face of the receptacle completed the dangerous circuit via the device cord-cap. See the right side of his third diagram - note the labeled "open in groundED leg" diagrammed between the service equipment and the receptacle in the diagram just to its right.

    To begin you need to understand the difference between Alternating Current and Direct Current to begin to understand what a "neutral" is and is not in AC circutry.

    Last edited by H.G. Watson, Sr.; 03-07-2010 at 08:46 AM.

  31. #31
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    Default Re: Why is a three pronged receptacle unsafe?

    I understand most of your post. One question I have about the third example. What would be the cause of the open neutral?
    Any number of things. Open neutrals are quite common in general purpose 15 and 20 amp branch circuits. Wires get loose or a bad connection in a wire nut. But by far the most common on 2 wire branch circuits is backstabed style receptacles. These are the ones where the wire just pushes into a hole on the back of the receptacle and a spring clamp holds tension on the wire. Over time it is common to see the connection fail and the neutral will open. This is a very real possibility in older and newer homes.
    This is a question unrelated to my original post but similar topic. If current travels on the hot wire through the appliance and then back on the neutral to the service panel. In the panel this same neutral wire is hooked to the neutral bus bar that ground wires also connect to. Why doesn’t the current flow back on these ground wires to the equipment?
    That's a very common question. The neutrals and grounds bond together only at one place ...the service equipment. The service equipment is the enclosure where the first means of disconnect for the dwelling is located. It can be in an enclosure by itself or it can be in a panelboard as a "MAIN " breaker. They bond in the service equipment because there is only one low impedance path for neutral and ground fault current to get to the utility transformer center tap at that point. That path is the service neutral. You can see this in the diagrams I posted. We also do not want any neutral to ground connections load side of the service equipment. This creates alternate paths for current on metal and wires that is dangerous and unwanted as we have been discussing in this thread.

    Why doesn’t the current flow back on these ground wires to the equipment?
    You could get pretty technical answering that question. Just remember that current will not flow on any path that doesn't have a potential difference in the direction it is flowing. A/C is 60 hz in the USA... meaning current moves at 60 cylce per second and each 1/2 cycle it reverses direction. So it is switching directions 120 times a second. If you look at the diagrams you will see the red dots of the completed circuit for a 120 volt branch circuit. One end of the circuit is the end point of the transformer winding and has a potential of 120 volts and the other end point is the midpoint of the transformer winding. What I have been calling the center tap. Here the voltage potential is 0 volts. So current is being 'pushed by the voltage with a potential difference of 120 volts regardless of the direction it is traveling in the ac circuit because it is always following a path of different voltage potential to the source or transformer. So current will not use the ground wires because they are all at 0 volts of potential same as the neutral wires that are connected to the applaince circuit. Current cannot flow when there is a potential difference of zero between two points.

    Remember the completed system circuit for 120 volts is from the end point of the transformer winding where the ungrounded conductor is connected thru the load and then to the midpoint (center tap) of the transformer winding over the grounded leg. The potential difference from end point to midpoint of the transformer winding is 120 volts and current will flow alternately between these two points of potential difference. Look at the 1st diagram.

    In contrast the equipment ground wires at one end are at 0 volts of potential in the service equipment and at the other end ..for example a receptacle they are also 0 volts. The equipment ground wires bond all the metal associated with the branch circuit to the same potential as the service neutral connected to the transformer midpoint.
    So current will not travel on the ground wires because there is no potential difference with the transformer at the ends of the ground wires. However touch a hot wire to the equipment ground and you have connected a 120 volt source to a 0 volt source and many amps of current will flow to the transformer resulting in the breaker tripping.

    Maybe someone here has a more simple explanation.

    Hope this helps.

    Last edited by Roger Frazee; 03-11-2010 at 09:33 AM.

  32. #32
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    Default Re: Why is a three pronged receptacle unsafe?

    I
    f the tester indicates everything is ok how do you know? Do you take face plates off on older homes and physically check a few?

    There are testers like this that will identify a boot leg

    Ideal SureTest Circuit Analyzers / ST-2D Circuit Analyzer

    You can also investigate if you notice wiring at the distribution panel that does not support 3 wire circuits.....ie...nothing serving as the equipment ground for the branch circuits. For example if you are inspecting the panelboard and notice that there are no equipment grounding means yet you have tested 3 wire grounding type receptacles installed on the premise wiring that show a good ground. At this point you must take a look and make sure a bootleg is not present on the receptacles or the possiblity of some other proper means of equipment ground being used... like emt metal conduit.




  33. #33
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    Default Re: Why is a three pronged receptacle unsafe?

    Ben,

    When I worked in a defense plant back ... oh, let's just say a very long time ago ... we had connectors similar to what you describe below, however, the connectors (as we called them were also 'male' and 'female' but not in terms of the pins and the sockets, but in terms of the overall 'plug' which would go into the overall 'socket'/'receptacle', which made the overall 'plug' the male 'connector' and the overall 'socket' the female connector.

    Quote Originally Posted by ben jacks View Post
    In some amorphic connectors, the contacts can have both pin and socket configured in the same connector to match the mating plug connector for a reversed interface. I believe these unique connectors can be found on comparable underwater instrumentation versions in submarines and other high tech equipment . rbj

    We used a lot of those connectors in the equipment I was calibrating and using, and in some of the items we were producing too.

    In fact, it was not uncommon to have a 'male' plug with female sockets in it for the male pins mounted in the 'female' socket - the terms 'male' and 'female' then referred to the overall configuration, not the actual connections within.

    Jerry Peck, Construction / Litigation Consultant
    Construction Litigation Consultants, LLC ( www.ConstructionLitigationConsultants.com )
    www.AskCodeMan.com

  34. #34
    Andy Jarchow's Avatar
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    Default Re: Why is a three pronged receptacle unsafe?

    That answers my questions. Thank you very much Roger and H.G.!
    [FONT='Times New Roman','serif']Have a great week.[/FONT]


  35. #35
    Roger Frazee's Avatar
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    Default Re: Why is a three pronged receptacle unsafe?

    Your welcome Mike

    You might want to spend some time understanding terms like grounding , grounded and ground. These take some time to understand and use correctly in your explanations on paper. I used the terms rather loosely in my explanations because I think it was less confusing for you. Understand also that the Grounding Electrode system (GES) is not the same as the Equipment Grounding Conductors (EGC). One is property protection (GES) and the other is Human Protection (EGC).

    Also understand that the white wire in a 3 wire or 2 wire 120 volt branch circuit is not a neutral but a grounded current carrying conductor aka grounded leg. It is referred to as a neutral by many but just want you to know that this is not technically correct. Neutrals are also grounded current carrying conductors but are different in that they carry the unbalanced current between two or more ungrounded (hot) conductors. An example is your Service Neutral. Another is the white wire in a range branch circuit to your kitchen. I made a few more diagrams to show you this difference.... attached below.

    There is a mountain of information as a home inspector that you need to get comfortable with and this will take years of experience and continued education. But your off to a good start because you like to know the why of your questions .. keep that attitude and the dots start to become connected...also attached is a drawing to get you started understanding terms about "ground"....

    Also understand that I am not a home inspector (HI) so I am not an authority on what you guys need to understand for inspecting a home or other dwelling. Just trying to give you information about electrical which I am comfortable with and was my trade for many years.

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    Last edited by Roger Frazee; 03-08-2010 at 11:35 PM. Reason: clarity

  36. #36
    Andy Jarchow's Avatar
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    Default Re: Why is a three pronged receptacle unsafe?

    Quote Originally Posted by Roger Frazee View Post
    Your welcome Mike

    You might want to spend some time understanding terms like grounding , grounded and ground. These take some time to understand and use correctly in your explanations on paper. I used the terms rather loosely in my explanations because I think it was less confusing for you. Understand also that the Grounding Electrode system (GES) is not the same as the Equipment Grounding Conductors (EGC). One is property protection (GES) and the other is Human Protection (EGC).

    Also understand that the white wire in a 3 wire or 2 wire 120 volt branch circuit is not a neutral but a grounded leg. It is referred to as neutral by many but just want you to know that this is not technically correct. Neutrals serve to carry the unbalanced current between two or more ungrounded (hot conductors). An example is your Service Neutral. Another is the white wire in a range branch circuit to your kitchen. I made a few more diagrams to show you this difference.... attached below.

    There is a mountain of information as a home inspector that you need to get comfortable with and this will take years of experience and continued education. But your off to a good start because you like to know the why of your questions .. keep that attitude and the dots start to become connected...also attached is a drawing to get you started understanding terms about "ground"....

    Also understand that I am not a home inspector (HI) so I am not an authority on what you guys need to understand for inspecting a home or other dwelling. Just trying to give you information about electrical which I am comfortable with and was my trade for many years.
    Roger,
    I really appreciate the time and effort you put into helping me understand. You went way beyond what I expected. I appreciate that very much.

    Thank you for your kind words.

    It’s been a pleasure learning from you.

    mk


  37. #37
    Roger Frazee's Avatar
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    Default Re: Why is a three pronged receptacle unsafe?

    Quote Originally Posted by ben jacks View Post
    Hi Roger,
    I use a 61-165... Dang good tester for in-wall anomalies also. rbj
    Sorry Ben I just noticed your post and I agree it is a very good tester for all aspects of branch circuit issues.


  38. #38
    Mike Leahey's Avatar
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    Default Re: Why is a three pronged receptacle unsafe?

    Thanks to all for the imput. There are a lot of well educated and experienced minds that participate in these discussions.


  39. #39
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    Default Re: Why is a three pronged receptacle unsafe?

    Hi guys, I was wondering what options the clients have when you have a situation where 3 prong outlets have been installed on a non grounded system. And how do you write it up to cya. Is complete system upgrade the only option here?
    Thanks
    Alan Highland


  40. #40
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    Default Re: Why is a three pronged receptacle unsafe?

    Quote Originally Posted by Alan Highland View Post
    Hi guys, I was wondering what options the clients have when you have a situation where 3 prong outlets have been installed on a non grounded system. And how do you write it up to cya. Is complete system upgrade the only option here?
    Thanks
    Alan Highland
    Apparently you missed post number 4:

    Quote Originally Posted by H.G. Watson, Sr. View Post
    Such receptacles, if present, are required to be protected via a Ground Fault Circuit Interupter, and individually labeled "No Equipment Ground".

    Two types of GFCIs - those that are designed to protect "personnel" and those that are designed to protect "equipment" (different tolerances for inbalanced levels/objectional current and trip time).

    In past versions of the NEC combination GFCI/receptacles were not allowed to protect downstream receptacles or outlets if there was no equipment ground conductor, this is no longer the case with more recent editions of the NEC.

    The GFCI device doesn't substitute for an egc but is thought to mitigate the lack of one as an alternate (to the circuit breaker) means to open the circuit. The GFCI serves to protect in some part injury to persons, where as the CB serves in part to protect damage to the electrical system.

    GFCIs do not require an equipment ground to determine an inbalance and trip (open). GFCI Circuit Breakers and GFCI receptacles (when installed correctly) open the hot when they trip. Portable GFCI devices such open both the Hot and the "neutral" (grounded conductor) when they trip, an added, and often essential protection (to persons) when working electricity in environments where multiwire branch circuits, wiring errors, etc. may be present (such as construction/temporary wiring or older installations with unknown/untested multi-generational adaptations are present).

    Remember also that EGC may be other than a wire conductor, ex. ribbon, bonded metalic conduit, etc., and in older flexible metalic conduit and cable may be undersized or not sufficient (but your tester may still show "grounded". Also remember that in decades past intermittant connections to water pipes, etc. beyond the service entrance were common place.

    Another often overlooked occurance in older homes is the presence of conductive/metalic face plates for switches and receptacles which are not bonded.

    Finally, regarding "two prong" receptacles, non-restrictive older two-prong receptacles which allow a polarized (one side wider blade) plug to be inserted in both directions; and the use of portable electric equipment, such as portable lamps, with older non-polarized cord caps (plugs) can present dangers of their own (ex. non-polarized cord cap on portable lamp can allow to be plugged in reverse - thus electrifying the shell of the lampp holder - and subjecting the user to dangerous objectional current should the user change the lamp (bulb) while the device is plugged in and make contact or arc, as well as when the integral switch is operated it opens and closes the grounded conductor not the hot. Similar "hazards" might be encountered with older ventillation fans which the "fan unit" is not hardwired but has a non-polarized cord cap, is removable from its mounts and is plugged into the integral receptacle within the shell. Older combination light fixtures, medicine cabinets, etc. which incorporated a convenience receptacle/shaver outlet often contained a non-grounded, and non-polarized receptacle - notably usually located just above or adjacent to a bathroom or kitchen sink, and oftentimes are wired not via a wall switch but having a metal switch on the light fixture/metalic bathroom cabinet itself.

    HTH.
    Grounding type receptacles are testing "no equipment ground". Explain the hazard and refer to a Licensed Electricial Contractor/Electrician to further examine, test, and suggest remediation for safety.


  41. #41
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    Default Re: Why is a three pronged receptacle unsafe?

    Quote Originally Posted by H.G. Watson, Sr. View Post
    Such receptacles, if present, are required to be protected via a Ground Fault Circuit Interupter, and individually labeled "No Equipment Ground".
    Those receptacles must also be labeled "GFCI Protected" too.

    - 406.3 General Installation Requirements.
    - - (D) Replacements. Replacement of receptacles shall comply with 406.3(D)(1), (D)(2), and (D)(3) as applicable.
    - - - (3) Non–Grounding-Type Receptacles. Where attachment to an equipment grounding conductor does not exist in the receptacle enclosure, the installation shall comply with (D)(3)(a), (D)(3)(b), or (D)(3)(c).
    - - - - (a) A non–grounding-type receptacle(s) shall be permitted to be replaced with another non–grounding-type receptacle(s).
    - - - - (b) A non–grounding-type receptacle(s) shall be permitted to be replaced with a ground-fault circuit interrupter-type of receptacle(s). These receptacles shall be marked “No Equipment Ground.” An equipment grounding conductor shall not be connected from the ground-fault circuit-interrupter-type receptacle to any outlet supplied from the ground-fault circuit-interrupter receptacle.
    - - - - (c) A non–grounding-type receptacle(s) shall be permitted to be replaced with a grounding-type receptacle(s) where supplied through a ground-fault circuit interrupter. Grounding-type receptacles supplied through the ground-fault circuit interrupter shall be marked “GFCI Protected” and “No Equipment Ground.” An equipment grounding conductor shall not be connected between the grounding-type receptacles.

    Jerry Peck, Construction / Litigation Consultant
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    www.AskCodeMan.com

  42. #42
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    Default Re: Why is a three pronged receptacle unsafe?

    JP: Yes, thanks, thought I had that in the first post, meant to, oops. Appreciate the catch.

    Yes, labeled "GFCI Protected, No Equipment Ground", when of course the GFCI protection is added.


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