Thread: Electric Receptacle What's-it

I found these receptacles on interior walls of two bedrooms. They have four horizontal prongs and live. I've seen them before, but can't recall what they were used for. I know some of you have! Thanks!

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The twp horizontal slots nowadays would indicate 240 volts. That receptacle however, will accept a standard 2 prong plug turn sideways. Because of the obvious age of the thing, when standards were hit or miss, I wouldn't want to say what voltages you could be getting from it.

I would recommend replacing it.

Thanks. Additional note: I did get current on two of the slots and considered the 240v idea. I couldn't figure out, though, what someone would plug in?? (interior wall = not an air conditioner).

You did not get current, you measured voltage. You measure current when something is in use.

Its an unsafe obsolete, painted over parallel AND tandem duplex outlet.

250V 10A loads or 125V possibly 15A but might be limited to 10A loads. Must be protected by 10 A fuses or CBs, so ancient that the panelboard that hosts them would be dangerous as we now know better.

Obsolete. Now its been painted over and MUST BE REMOVED. Wiring of this vintage would be undersized and UNSAFE (such as undersized neutrals, lacking grounding and UNDERSIZED by temperature and amperage hot conductors). If that's a metalic face plate that's been painted over its doubly dangerous.

Here is an example of an "extremely old 'Nurpolian' brand black parallel and tandem duplex outlet rated at 250 V 10A/125 V."



Many older (pre-1960s NEMA standards) North American receptacles have two different current and voltage ratings, more recently (post 30s pre 60s) commonly 10 A 250 V/15 A 125 V. This has to do with a peculiarity of the National Electrical Code from 1923 to the 1950s. Originally, receptacles were rated at 10 A 250 V, because the NEC limited lighting circuits to 10 A. In 1923, the code changed to allow lighting circuits to be fused at 15 A, but the previous 10 A rule still applied to circuits over 125 V. The higher voltages were rarely used for lighting and appliances. Most receptacles with this rating are of the "T-slot" type. This type of rating was phased out in the 1950s, and finally abolished in the 1960s with the adoption of the current NEMA standards.

Thanks for that H.G., In all my years (too many) I never seen one of those tings, yet. Now I won't have to act confused

Thank you, HG, for the history lesson. Not many homes in my area are that old, but now I will be prepared. Much appreciated.

Thanks HG for the education! That was great.

Thanks to H.G., I was able to sound somewhat intelligent in my report! What old device would have required the 240v do you suppose?

Originally Posted by Donald Bissex

Thanks to H.G., I was able to sound somewhat intelligent in my report! What old device would have required the 240v do you suppose?

Maybe an electric heater, if it is in a living room. A 240 volt heater draws half as much current as a 120 volt heater for an equivalent amount of heat.

required the 240v do you suppose?Maybe an electric heater, if it is in a living room. A 240 volt heater draws half as much current as a 120 volt heater for an equivalent amount of heat.

John Kogel, RHI, BC HI
--------------------------------------------------------------------------------------------------------------------

Actually the same amount of current is 'drawn', only that it is divided between the two line conductors as opposed to just one as in the case of a 120 volt single phase circuit.
This does not hold true in a 3 phase circuit however.

Example would be a well pump that can be wired 120 or 240 volt.
Same horse power motor, same energy used.
Starting characteristics are usually better on 240v but I won't get into the reasons for that on this thread... way off topic.

Great bit of electrical history. On a heater that is connected to either 120 or 240 volts, the same amount of current is not "drawn". If the heating element could withstand 240 volts without burning up, it would take half / 50% of that draw, ( amperage ), at 120 volts. There is no 5 amps on each side to total 10 amps. It is 10 amps or it is 5 amps, but never 5 on each side totaling 10. There are no three phase elements; only single phase. There are manufactured three phase electrical heaters. Three single phase elements can be and are connnected to three phase circuits, but the elements remain single phase and each element is supplied by only two wires.

What I said is correct and it can be misinterpreted dozens of ways, that is also correct.

Originally Posted by John Kogel

What I said is correct ...

Originally Posted by John Kogel

A 240 volt heater draws half as much current as a 120 volt heater for an equivalent amount of heat.

Originally Posted by bob smit

Actually the same amount of current is 'drawn', only that it is divided between the two line conductors as opposed to just one as in the case of a 120 volt single phase circuit.

John,

I believe the above comments correcting the incorrect posted information were correcting Bob, not you.

P = IE
P (power) = I (amps) x E (voltage)
2400 watts = 20 amps x 120 volts
2400 watts = 10 amps x 240 volts

The power use did not change, the amps changed in direct proportion to the change in voltage, i.e., voltage doubled, amps halved, power stayed the same.

On the other hand, if the voltage doubles and the amps stays the same, then the power also doubles.
2400 watts = 20 amps x 120 volts
4800 watts = 20 amps x 240 volts

However, if the voltage doubles and the amps double too, then the power quadruples.
2400 watts = 20 amps x 120 volts
9600 watts = 40 amps x 240 volts

Originally Posted by H.G. Watson, Sr.

This has to do with a peculiarity of the National Electrical Code from 1923 to the 1950s. Originally, receptacles were rated at 10 A 250 V, because the NEC limited lighting circuits to 10 A. In 1923, the code changed to allow lighting circuits to be fused at 15 A, but the previous 10 A rule still applied to circuits over 125 V. The higher voltages were rarely used for lighting and appliances. Most receptacles with this rating are of the "T-slot" type. This type of rating was phased out in the 1950s, and finally abolished in the 1960s with the adoption of the current NEMA standards.

Watson,

Do you have some code references on the above declarations?

I've looked back through my old NEC codes and have not been able to find anything which states or implies the above.

Originally Posted by Jerry Peck

Watson,

Do you have some code references on the above declarations?

I've looked back through my old NEC codes and have not been able to find anything which states or implies the above.

Jerry - I find it very difficult to locate things in the pre-1937 codes, since they don't have the same numbering systems. It looks like the 10-amp limitation was in Rule 23d in the 1913 and 1918 Code. I don't have a 1920 code, though the rule was still there. In the 1923 NEC, the revised rule was in section 807d

It looks like the rule that required 10 amp protection for circuits with lighting outlets was to also protect the 16 or 18 gauge fixture wire or appliance cord. The 1923 NEC has a recommendation that "attachment plugs" (which it also calls "convenience outlets") be used instead of sockets that can also be used with ordinary lamps. I don't understand what this has to do with the rating of the receptacle itself, nor have I been able to locate the 10 amp limitation in codes after 1923. I'm not saying it isn't there - just that I haven't found it.

Check out the 5th paragraph on the second page of the attachment.

Douglas Hansen
Code Check- Help With Building Codes

Originally Posted by Douglas Hansen

Jerry - I find it very difficult to locate things in the pre-1937 codes, since they don't have the same numbering systems. It looks like the 10-amp limitation was in Rule 23d in the 1913 and 1918 Code. I don't have a 1920 code, though the rule was still there. In the 1923 NEC, the revised rule was in section 807d

It looks like the rule that required 10 amp protection for circuits with lighting outlets was to also protect the 16 or 18 gauge fixture wire or appliance cord. The 1923 NEC has a recommendation that "attachment plugs" (which it also calls "convenience outlets") be used instead of sockets that can also be used with ordinary lamps. I don't understand what this has to do with the rating of the receptacle itself, nor have I been able to locate the 10 amp limitation in codes after 1923. I'm not saying it isn't there - just that I haven't found it.

Check out the 5th paragraph on the second page of the attachment.

Douglas Hansen
Code Check- Help With Building Codes

Douglas,

Do you have the wording in your 1913 and 1918 editions for that?

Unfortunately, my largest gap in the NEC editions that I have is right there - I jump from the 1905 to the 1925 (I used to have a 1915 but misplaced it during my move from South Florida):
- I have the 1897; jump to the 1905; then jump to 1925; 1928; 1931; 1935 & Handbook; 1937 & Handbook; 1946 Handbook - code delayed until 1947, also have the 1946 revisions to the code; 1947 & Handbook; 1951 Handbook; 1953 & Handbook; 1956; from 1959 to present I have the codes and handbooks.

If you have some of the wording you are referring to, I may be able to find it in the 1905 edition, but so far I have not found a limitation as such in it. I see the reference in that document, but nothing in the 1905 which states that.

It is possible that such a limitation was put in after the 1905 edition, then removed again.

I look forward to the wording in those sections so I can try to find it in the 1905 - thank you in advance or those sections.

I would expect it isn't there in the 1905. Looking at the attached document, it appears to be much more explicit in 1918 than in 1913. I have a 1907 document on lighting (downloaded from a google search) that doesn't mention this either.

Interesting research for a wet and foggy Sunday.

Douglas Hansen
Code Check- Help With Building Codes

Douglas,

Thank you, but that does not require branch circuits to be protected by 10 amp fuses.

That is similar to my 1905 which states:
- 21.
- - e. The rated capacity of fuses must not exceed the allowable carrying capacity of the wire as given in No. 16. Circuit-breakers must not be set more than 30 percent above the allowable carrying capacity of the wire, unless a fusible cut-out is also installed in the circuit.
- - - (In a smaller font designating it as a note, today it would be a FPN)
- - - - In the arms of fixtures carrying a single socket a No. 18 B & S gage wire supplying only one socket will be considered as properly protected by a six ampere fuse.

In d. above that, it says this:
- 21.
- d. Must be so places that no set of incandescent lamps requiring more than 660 watts, whether grouped on one fixture or on several fixtures or pendants, will be dependent upon one cut-out. Special permission may be given in writing by the Inspection Department having jurisdiction for departure from this rule in the case of large chandeliers, stage borders, and illuminated signs.
- - (Then the equivalent of a FPN again in smaller font)
- - The above rule shall also apply to motors when more than one is dependent on a single cut-out.
- - The fuses in the branch cut-outs should not have a rated capacity greater than 6 amperes on 110 volt systems, and 3 amperes on 220 volt systems.
- - The idea is to have a small fuse to protect the lamp socket and the small wire used for fixtures, pendants, etc. It also lessens the chances of extinguishing a large number of lights if a short circuit occurs.
- - On open work in large mills approved link fused rosettes may be used at a voltage of not over 125 and approved enclosed fused rosettes at a voltage of not over 250, the fuse in the rosettes not to exceed 3 amperes, and a fuse of over 25 amperes must not be be used in the branch circuit.
- - All branches or taps from any three-wire system which is directly connected to lamp sockets, must be run as two wire circuits, when the difference of potential between the two outside wires is over 250 volts.

As can be seen in d., the smaller fuses are not necessarily for the protection of the branch circuits, but for the protection of the wiring within the lighting fixtures. As such, one could have installed larger protection for the branch circuit and installed individual protection for each lighting fixture.

At least it was that way in 1905.

I see what you mean (although I wonder if folks in 1905 would have put that fine a point on it). Perhaps it also had this interpretation 1913. I have a 1913 Terrell Croft handbook which does not include code text, only commentary, and he doesn't say anything about it then.

Would you agree that it did by 1918?

The verbiage on page 53 (page 5 of the pdf) says "The fuses in the branch cut-outs protecting circuits of 660 watts or less shall not have a rated capacity greater than that given in the following table:
125 volts or less.....10 amperes
125 to 250 volts......6 amperes"

And from the other comments from NFPA and Croft, we can see that 1920 must have also had a version of this.

The group of people like us that care what the code intended 100 years ago is probably small.

Douglas Hansen
Code Check- Help With Building Codes

It is unclear just what you presume to question.

IF you are suggesting that what I represented ON THE TOPIC OF THIS DISCUSSION, which IS a 250V/125V 10A parallel AND tandem duplex receptacle, was in any way incorrect, regarding the history of requirement that branch circuits which supplied appliances (As defined by the section) or lighting with voltages other than (higher) than 125V were limited to circuit protection at 10 amps, and that lighting and appliance branch circuits at 125V were limited at 15 amps (and previously at 10 amps prior to 1923) from 1923 to 1950, for those blade receiving receptacles (which the Code and the newly created UL referred to as "receptacles for attachment plugs (applince or convenience outlets) for the branchcircuits discussed, you are indeed wrong (again) to have done so.

There were so VERY many developments and changes during the "holes" in your library collection, I cannot and WILL NOT begin to address your lack of historical knowledge, reading materials, budget, or comprehension.

You can easily acquire scanned versions of ALL the editions missing from your "library" from NFPA.org, at less than 30 bucks apiece. Read away.

Attached document, see its pgs. 18 & 19 of 41, 1925 Sect. 807, "Fuses for Lighting and Appliance Branch Circuits", see # f which reads as follows:

f. Branch circuits in general, and except as described below, shall be protected by fuses of no greater rated cpacity than

15 amperes .......... at 125 volts or less
10 amperes .......... at 126 to 250 volts

Be sure to NOT overlook the definitions for the section (807) at "a." which specifically define the terms used in the section, which are:
"Branch Circuit"
"Outlet" and
"Appliances".

Protection of Electrically Heated Appliances are at Section 811, bottom of the attached document's page 22 of 41.



The TOPIC is NOT mogul type sockets/receptacles nor the branch circuits supplying same.

Originally Posted by Douglas Hansen

Would you agree that it did by 1918?

The verbiage on page 53 (page 5 of the pdf) says "The fuses in the branch cut-outs protecting circuits of 660 watts or less shall not have a rated capacity greater than that given in the following table:
125 volts or less.....10 amperes
125 to 250 volts......6 amperes"

"Would you agree that it did by 1918?"

I would like to agree, here is why I disagree with that (as you say, the group of people who care what the code intended 100 years ago is small, but understanding where it started and how it has changed goes a long way toward understanding where it is today):
- From page 52 of that pdf:
- - 23. Automatic Cut-outs - continued.
- - - c. Must be in plain sight, or enclosed in an approved cabinet, and readily accessible. They must not be placed in the canopies or shells of fixtures.
- - - - (paragraph not applicable to discussion so I did not type it)
- - - d. Must be so placed that no set of small motors, small heating devices or incandescent lamps, whether grouped on one fixture or on several fixtures or pendants (nor more than 16 medium size or 25 candelabra size sockets or lamp receptacles) requiring more than 660 watts will be on one cut-out.

Between c. and d. the code implies that each fixture could be protected by its own cut-out, as long as the cut-out is not "placed in the canopies or shells of fixtures", which indicates that the cut-out could be placed near the fixture as long as it was "Must be in plain sight, or enclosed in an approved cabinet, and readily accessible."

Then it continues with what you quoted: (bold and underlining are mine)
- "The verbiage on page 53 (page 5 of the pdf) says "The fuses in the branch cut-outs protecting circuits of 660 watts or less shall not have a rated capacity greater than that given in the following table: "

"The fuse in the branch cut-outs ... " could be taken to mean, in conjunction with the other above sections, that the branch circuit itself may be protected to the ampacity rating of the conductors of the branch circuits, but that taps (see the first sentence on page 53) from those branch circuits and with the taps "directly connected to lamp sockets" and "All wires of all branch or tap circuits which are directly connected to lamp sockets or other translating devices must be protected by proper fuses." may be protected by smaller cut-outs (fuses) based on what is connected to each specific tap.

This is further implied here on page 51:
- 23. Automatic Cut-outs (Fuses and Circuit-Breakers).
- - b. Must be placed at every point where a change is made in the size of wire [unless the cut-out in the larger wire will protect the smaller (see No. 18)].

Douglas, it sure can be confusing trying to understand where they were 100 years ago when we have the benefit of 100 years of hindsight and are looking into advances in the future. Our current knowledge can sometimes make it difficult to understand what they were considering based only on what they knew at the time and what they were trying to protect against at the time.

However, there are other times where, from that simpler time in the past, they stated what they meant in plainer language than we use today as we are trying to cover what we know may be coming down the pike in the near future, whereas they were trying to cover for what they knew at the time and what they knew was coming in the near future.

When you look at the dates of the code editions, supplements and prints of the code from 1897 until 1962 compared to the dates from 1962 on, we realize that they were in a whirlwind of progress and changes in the electrical industry. We are making strides at a great rate of progress in the technical tweaking of the code, they were making strides at a great rate of progress in the basic practices of electrical wiring and installations. One can think of it as they were laying the railroad tracks, we are simply updating the trains running on those tracks.

Excellent discussion on the old code, by the way.

There was a point in time when there were two competing types of cord cap/receptacle designs in fairly popular use for the (then) 110 volt supply for household use. One type had the familiar type parallel blades, the other had in-line blades. The OPs picture is one type of receptacle produced that would take either kind of cord cap (plug). A receptacle that does the same thing has double "T" slots and this type was produced into the 50s.

Pre NEMA, there were a number of various receptacle/cord cap configurations for different voltages, some of which could be connected but weren't intended to fit.

Maybe available here:
NBFU 70: Electric Lighting with Instructions for the Proper Inspection of Equipments. Electric Lighting and the Underwriters' Standard Requirements in Reference thereto with Instructions for the Proper Inspection of Electric Light Equipments Illustra

Originally Posted by H.G. Watson, Sr.

Many older (pre-1960s NEMA standards) North American receptacles have two different current and voltage ratings, more recently (post 30s pre 60s) commonly 10 A 250 V/15 A 125 V. This has to do with a peculiarity of the National Electrical Code from 1923 to the 1950s. Originally, receptacles were rated at 10 A 250 V, because the NEC limited lighting circuits to 10 A. In 1923, the code changed to allow lighting circuits to be fused at 15 A, but the previous 10 A rule still applied to circuits over 125 V. The higher voltages were rarely used for lighting and appliances. Most receptacles with this rating are of the "T-slot" type. This type of rating was phased out in the 1950s, and finally abolished in the 1960s with the adoption of the current NEMA standards.

Mr. Watson that was interesting. I never had any need to concern myself with an older code like this, but your comments got me interested. I dug out my oldest NEC, 1947, and sure enough it did allow 10a at 250 v.

Section 4161. Rating and Type.
Receptacles installed for the attachment of portable cords shall be rated not less than 15 amperes, 125 volts, or, 10 amperes, 250 volts, and shall be of a type not suitable for the use as lampholders.

I don't know why, but this caught my fancy. Thanks for posting it as I didn't have the slightest idea what the recept was used for.

Originally Posted by H.G. Watson, Sr.

It is unclear just what you presume to question.

Not sure if you are referring to me or not, but if you are, this part:

Attached document, see its pgs. 18 & 19 of 41, 1925 Sect. 807, "Fuses for Lighting and Appliance Branch Circuits", see # f which reads as follows:

f. Branch circuits in general, and except as described below, shall be protected by fuses of no greater rated cpacity than

15 amperes .......... at 125 volts or less
10 amperes .......... at 126 to 250 volts

Be sure to NOT overlook the definitions for the section (807) at "a." which specifically define the terms used in the section, which are:
"Branch Circuit"
"Outlet" and
"Appliances".

You seem to have overlooked the definitions, by overlooking the definitions one can try to surmise that you might be correct, however, being as you specifically pointed out "Be sure to NOT overlook the definitions" I can only surmise that you did read the definitions, then ignored them - oh well, it is not unusual for you to ignore things.

As per my discussion with Douglas, that definition further defines and goes with what I was pointing out to Douglas - that the automatic cut-out (fuse or breaker) could be installed at or near the fixture, and the definition of branch circuit supports that:
"Branch Circuit"-
Branch circuit is that portion of a wiring system extending beyond the final fuse or fuses protecting it.
For particular applications to motor branch circuits, reference should be made to Article 808.

In those old houses, it was not unusual to find fuses at various locations around the house, and those fuses would be protecting the "branch circuit" as known and described "back then", not the same as the we understand the term to mean today:
- Branch Circuit. The circuit conductors between the final overcurrent device protecting the circuit and the outlet(s).

In today's installations, the branch circuit is from the panel (which contains the breaker or fuse for older installations) to the receptacles, back then, the branch circuit was still from "the final" fuse, but the fuse was not always located in a panel at some location with all or most of the other breakers (there could well be two or more panels in today's installations, and the branch circuit would be the conductors from those breakers out to the receptacles and outlets). I have not seen a fuse or breaker installed near a light fixture or group of light fixtures in a very long time, back then it was done.

So, yes, as you say, the "branch circuit" ratings were limited to:
- 15 amperes .......... at 125 volts or less
- 10 amperes .......... at 126 to 250 volts

However, in today's thinking, the conductors going to the line side of the final fuse or circuit breaker are "feeders", and today those "feeders" go to a panelboard which then goes out to the receptacles and other outlets around the house with no additional fuses (or breakers) between the the panelboard and the light fixture.

- Feeder. All circuit conductors between the service equipment, the source of a separately derived system, or other power supply source and the final branch-circuit overcurrent device.

Watson, you need to open your mind as well as your eyes to understand what is being addressed AND DEFINED "back then" AT THAT TIME when electrical systems were installed differently than they are installed today.

Okay, let's go here - based on the definitions in today's NEC (I'll use the 2008 as many are using that edition):
- Branch Circuit. The circuit conductors between the final overcurrent device protecting the circuit and the outlet(s).
- Feeder. All circuit conductors between the service equipment, the source of a separately derived system, or other power supply source and the final branch-circuit overcurrent device.

From the service equipment to the panelboard, the conductors are defined as: _________ ?

From the panelboard to the receptacle outlets and lighting outlets, the conductors are defined as: _______ ?

From the panelboard to the UNfused disconnect at the air conditioner condenser unit, the conductors are defined as: _______ ? And the conductors from the UNfused disconnect are defined as: ___________ ?

From the panelboard to the fused disconnect at the air conditioner condenser unit, the conductors are defined as: _______ ? And the conductors from the fused disconnect are defined as: ___________ ?

Yes, it is a trick question (one must read and understand the definitions, that's the trick).

Oops, my bad, post 11
My post was in relation to a well pump situation where the installer was telling folks that the wiring of his pumps saves the customer half on his energy bill.
The first paragraph of my post was not thought thru, sorry.
The second was correct in that for the same amount of energy in Watts, the voltage and current are inversely proportional in a circuit of 100% power factor such as a purely resistive load. Tis why purely resistive appliances are rated in watts on their nameplates.

Motors and capacitive loads are rated in VA (volts x amps) due to inductive and capacitance losses where the power factor is not unity.
Note that capacitive reactance is also used to bring inductive reactance back in phase by utility companies and factories.

There, I feel better now
Here is some info on the well issue I had with the well contractor.
Compare 120Volts to 240Volts - Is one More Energy Efficient?