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  1. #1
    Jim Ball's Avatar
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    Default Sub fed from double tap on main lugs

    Here is my first post.
    In the main panel I found a #12 wire that is tapped into the main lugs that fed a 20 sub panel some 2 feet away. The installation of the sub appeared to be done in a less than professional manner including the #12 Romex was strung across the concrete wall unsupported with no conduit, missing grommets, opening in the panels, etc. I listed the defects and recommend further evaluation and repair by a licensed electrician.
    When the licensed electrician showed up, who was the same one who did the original work, he claimed I didnít know what I was talking about. I advised the buyer to have the seller have his licensed electrician put it in writing that everything was fine on his companies letter head, He did it!.
    Now my most important question is the #12 Romex that feeds the sub panel. Since it is double tapped on the main lug and not protected by a breaker why hasnít vaporized by now? What an I missing?

    Thanks
    Jim Ball

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  2. #2
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    Default Re: Sub fed from double tap on main lugs

    It hasn't vaporized because there hasn't been enough of a draw on the panel to overheat the insulation. If the panel isn't in use, or doesn't pull much amperage through the #12 wire, the wire will remain unchanged. A lot of times, there isn't a problem with wiring like that, until there is a problem.

    I'm talking about the secondary panel, not the main panel. What happens in the main panel is in most ways not connected to the secondary panel. Think of the secondary panel pulling current through the wire. It isn't pushed through the #12 by the main lugs, but pulled through by whatever is happening at the other end of the secondary panel.

    You are correct that it is not correct. I'm pretty surprised that he put his opinion in writing.

    Jim Robinson
    New Mexico, USA

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    Default Re: Sub fed from double tap on main lugs

    Jim everything you said is right! Good find! Makes you wonder if the electrician is a few bricks short of a load.

    Are you going to report him?

    Raymond Wand Home Inspection Service
    http://www.raymondwand.ca
    The value of experience is not in seeing much, but in seeing wisely.

  4. #4
    John Arnold's Avatar
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    Default Re: Sub fed from double tap on main lugs

    Jim - First of all, Welcome to the Board!

    Please update your profile so we know where you're from. Sometimes it helps with responses.

    As Jim Robinson stated, the #12 isn't going to have any current just as a result of being tapped into the main. Something has to draw current through it. It's still wrong, of course.


  5. #5
    Jerry Peck's Avatar
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    Default Re: Sub fed from double tap on main lugs

    First, Jim, welcome to THE inspectors board.

    Second:

    Quote Originally Posted by Jim Ball View Post
    In the main panel I found a #12 wire that is tapped into the main lugs
    That's a simple part, that is not allowed ... unless those main lugs are identified for 2 conductors, and for those different wire sizes - which is highly unlikely, so, the simple answer is "that is not allowed because you are not allowed to multiple tap terminals, breakers included".

    that fed a 20 sub panel some 2 feet away.
    That's the hard part, see below for answer.

    Now my most important question is the #12 Romex that feeds the sub panel. Since it is double tapped on the main lug and not protected by a breaker why hasnít vaporized by now? What an I missing?
    As the others have said, 'because it has not had much current through it yet.

    Now, back to the hard part ...

    From the 2008 NEC. (underlining and bold are mine)
    - ARTICLE 240 Overcurrent Protection
    - - II. Location.
    - - - 240.21 Location in Circuit.
    - - - - (B) Feeder Taps. Conductors shall be permitted to be tapped, without overcurrent protection at the tap, to a feeder as specified in 240.21(B)(1) through (B)(5). The provisions of 240.4(B) shall not be permitted for tap conductors.
    - - - - - (1) Taps Not over 3 m (10 ft) Long. Where the length of the tap conductors does not exceed 3 m (10 ft) and the tap conductors comply with all of the following:
    - - - - - - (1) The ampacity of the tap conductors is
    - - - - - - - a. Not less than the combined calculated loads on the circuits supplied by the tap conductors, and
    - - - - - - - b. Not less than the rating of the device supplied by the tap conductors or not less than the rating of the overcurrent protective device at the termination of the tap conductors.
    - - - - - - (2) The tap conductors do not extend beyond the switchboard, panelboard, disconnecting means, or control devices they supply.
    - - - - - - (3) Except at the point of connection to the feeder, the tap conductors are enclosed in a raceway, which shall extend from the tap to the enclosure of an enclosed switchboard, panelboard, or control devices, or to the back of an open switchboard.
    - - - - - - (4) For field installations where the tap conductors leave the enclosure or vault in which the tap is made, the rating of the overcurrent device on the line side of the tap conductors shall not exceed 10 times the ampacity of the tap conductor.
    - - - - - - - FPN: For overcurrent protection requirements for panelboards, see 408.36.

    Thus, *IF ALL* of the above was done (and it was not), then the overcurrent protection rating for the #12 feeder, which has a 20 amp rating, *COULD BE AS MUCH AS ... 200 AMPS at the line side where the feeder is tapped.

    However, all of that 'hard part' is moot because "(3) Except at the point of connection to the feeder, the tap conductors are enclosed in a raceway" NM cable was used and it was not in a raceway. Now, it also sounds like other things were not done, so "just installing that feeder in a raceway" will not take care of the problems.

    Jerry Peck, Construction / Litigation Consultant
    Construction Litigation Consultants, LLC ( www.ConstructionLitigationConsultants.com )
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  6. #6
    Jim Ball's Avatar
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    Default Re: Sub fed from double tap on main lugs

    Thanks Gentlemen


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    Default Re: Sub fed from double tap on main lugs

    [QUOTE=Jim Robinson;63258] I'm pretty surprised that he put his opinion in writing.[/QUOTE


    It's pretty amazing what people will put in writing.

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    Default Re: Sub fed from double tap on main lugs

    Eric,

    Now THAT is some voltage ... 143.3 volts! I'm guessing they have a neutral problem.

    But THEN you go and top it off with 73.8% voltage drop? Yikes! More confirmation that there is a neutral problem.

    Jerry Peck, Construction / Litigation Consultant
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    Default Re: Sub fed from double tap on main lugs

    Jerry,

    A weird job. All kinds of problems. I remember we had no power in a bathroom - till we found that it was controlled by a bedroom light switch. Things were so bad that I turned off all the power in the townhouse before I left. Seller called me up when he got home - pretty upset. He was in a real pickle. He had his brother-in-law electrician do all this work to replace aluminum wiring. The receipt was left out for the inspection to help promote the home's upgrade.

    His major problem was that he was going to have to go through his ex-wife to reach the b-in-l. Apparently she was a REAL B---- and he absolutely could not stand the thought of having to call her. I think that the call was more horrible to him then the fact that his home was now unsafe. I've always wondered if the brother-in-law did this on purpose to satisfy some desire to get even.

    Last edited by Eric Barker; 11-25-2008 at 06:36 PM. Reason: grammer
    Eric Barker, ACI
    Lake Barrington, IL

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    Default Re: Sub fed from double tap on main lugs

    I think I would just chalk that one up to experience, and leave the brother in law out of the mix, if I were the seller. It doesn't seem like he was very competent anyhow, so why bother with the ex wife and the rest.

    Call someone who knows what they are doing.

    Jim Robinson
    New Mexico, USA

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    Default Re: Sub fed from double tap on main lugs

    Quote Originally Posted by Jerry Peck View Post
    I'm guessing they have a neutral problem.

    More confirmation that there is a neutral problem.
    I was expecting some questions on why that indicates the above?

    Jerry Peck, Construction / Litigation Consultant
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  12. #12
    Donald Merritt's Avatar
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    Default Re: Sub fed from double tap on main lugs

    Got to be a loose neutral at the electrical panel or at the meter base.

    Don Merritt
    Germantown, Tennessee


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    Default Re: Sub fed from double tap on main lugs

    Quote Originally Posted by Jerry Peck View Post
    I was expecting some questions on why that indicates the above?
    Jerry - Can you expand on why you believe there is a neutral problem, please?

    Have a great Thanksgiving, and I hope Mrs. Peck feels better soon.


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    Default Re: Sub fed from double tap on main lugs

    John,

    We all know that the utility company supplies all buildings from the same generating plants and distribution lines, which means the 143 volts is a localized problem at that one structure.

    We also know that that one structure, like all other structures, is being feed with a 120 volt / 240 volt service (presuming it is not an old 120 volt service).

    We also know that structure is really only being supplied with 240 volts between the two phase conductors, and that there is a center tap making the voltage 120 volts from either phase conductor. That is what the neutral does, it establishes a control point between the two phase conductors.

    Now, let's presume that there is no neutral (the neutral is open) and you two hot phase conductors and a grounding system, as does the transformer. Without the neutral conductor, the grounding system will act as a path back to the transformer, and, with the grounding system and neutral bonded together at the service, that grounding system is trying to serve as the control point between the two phase conductors.

    First, let us presume there is no current flow, you would measure close to 120 volts between ground and each phase conductor.

    Now, let us presume there is current flow through only one phase conductor and through the grounding system back to the transformer. The grounding system is not a low impedance path (not a low resistance, not like the neutral conductor was), so current through it will cause a voltage drop across the grounding path to the transformer, because the ground path to the transformer is acting as one large wattage, low ohm, resistor. Let us presumer there is 10 amp flow on that one phase conductor and the ground path, and let us presume there is 2.2 ohms resistance in the ground path. Now we do the math, E=IR or voltage=current x resistance or E=10 amps x 2.2 ohms or E=10x2.2 or E=22 volts. That means there is 18 volts dropped (used) across the ground path.

    240 volts - 120 volts on one phase leg = 120 volts on the other phase leg

    120 volts - 22 volts = 98 volts left for the other circuit

    240 volts - 98 volts = 142 volts across the circuit, including the 22 volts across the ground path.

    Now, to complicate matters, let's presume there is current flow on both phase conductors, but that it is not equal, as this would almost always be representative of actual conditions. Let us say there is 35 amps on one phase conductor and 45 amps on the other phase conductor, with that 10 amps difference going through the ground path to the transformer.

    Only that is not more complicated, is it? Because we are back to the same 10 amps through the ground path.

    Okay, we now have 142 volts measured across that circuit.

    Now, how does the voltage drop % going up confirm that?

    When the voltage drop was measured, the tester put an *additional 20 amps* on that circuit. Thus, there was either 10 amps or 30 amps through the ground path, depending on which circuit the tester was place. Putting the tester on the circuit with the higher voltage now put 30 amps through the ground path - the original 10 amps plus the 20 amps for the test.

    It's really not that easy for the math, but that is representative of what is happening and allows you to see what can happen when there is no, or a poor, neutral connection/conductor through which the center point is referenced. In effect, the neutral is "floating", i.e., the neutral is no longer "effectively tied to ground" and thus "floats between the two phase conductors based on the current flow".

    Hope that helped.

    And thank your for the good wishes.

    Hope you are having a good turkey day - we had a couple of slices of sliced turkey from a package, just to say 'Yeah, we had turkey on Thanksgiving.'

    Oh, and some pumpkin pie with Cool Whip on it. Pumpkin pie is my favorite.

    Jerry Peck, Construction / Litigation Consultant
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  15. #15
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    Default Re: Sub fed from double tap on main lugs

    What Jerry is trying to say is without a good neutral the utility transformer is not balanced due to the design of the transformer and you will see these strange voltages at the electrical panel.

    Don Merritt


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    Jerry Peck's Avatar
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    Default Re: Sub fed from double tap on main lugs

    Quote Originally Posted by Donald Merritt View Post
    What Jerry is trying to say is without a good neutral the utility transformer is not balanced due to the design of the transformer and you will see these strange voltages at the electrical panel.

    ... and throughout the house, and the voltages will change, based on what happens to be operating at the time you make your measurements.

    Don't be surprised that the voltage is different when you go back to "recheck it because something weird is going on", yeah, something weird IS going on.

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