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Thread: Any tricks for tracing bad neutral?

  1. #1
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    Any tricks for tracing bad neutral?

    I do a fair amount of electric service, enough to know when a customer asks how long to find the cause of defective circuit that I tell them twenty minutes to a full day. I had one the other day with a long time client that gave all the signs of a half burnt neutral connection someplace. I told him I would swing by and have a look but was swamped with a/c calls and if I could not find in an hour or so I would refer him to another place I trust.

    Thinwall between floor and subfloor so no breaks in tracking the runs visually from basement, etc. I also started seeing BX coming into some boxes from god knows where and finally after about an hour and a half I told him to call my referral. If it had only been a couple outlets and a lost hot wire I would have come back another day and he would have waited. I did not want to chance that with a neutral that was dimming and brightening stuff depending on what switch you flipped. The month before I had a client that had for days gone about life with a completely disconnected neutral at the Edison splice above the roofline!

    The question I guess is are there any means to narrow down where to begin looking or is it just box, to box, to box, to ceiling fan/light, to box.....? First thing I did was check and tighten all the neutrals in the panel.

  2. #2
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    Would a open / high resistance neutral out in the building do that? Cause one circuit to bright/dim another circuit?

    I would be looking back at the panel and before it. The bright/dim thing happens because of the two legs in the panel becoming unbalanced - more circuits active on one of the incoming legs than on the other incoming leg - with a non-semi functioning neutral to provide a balance so the circuit voltages don't vary.

    On the other hand; what the hell do I know? <g>

    PHM
    --------


    Quote Originally Posted by Glennhvac View Post
    I do a fair amount of electric service, enough to know when a customer asks how long to find the cause of defective circuit that I tell them twenty minutes to a full day. I had one the other day with a long time client that gave all the signs of a half burnt neutral connection someplace. I told him I would swing by and have a look but was swamped with a/c calls and if I could not find in an hour or so I would refer him to another place I trust.

    Thinwall between floor and subfloor so no breaks in tracking the runs visually from basement, etc. I also started seeing BX coming into some boxes from god knows where and finally after about an hour and a half I told him to call my referral. If it had only been a couple outlets and a lost hot wire I would have come back another day and he would have waited.

    I did not want to chance that with a neutral that was dimming and brightening stuff depending on what switch you flipped.

    The month before I had a client that had for days gone about life with a completely disconnected neutral at the Edison splice above the roofline!

    The question I guess is are there any means to narrow down where to begin looking or is it just box, to box, to box, to ceiling fan/light, to box.....? First thing I did was check and tighten all the neutrals in the panel.
    PHM
    --------
    The conventional view serves to protect us from the painful job of Thinking

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  4. #3
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    Damn; let me try this again:

    Would a open / high resistance neutral out in the building do that? Cause one circuit to bright/dim another circuit?

    I would be looking back at the panel and before it. The bright/dim thing happens because of the two legs in the panel becoming unbalanced - more circuits active on one of the incoming legs than on the other incoming leg - a fully functioning neutral provides a balance so the circuit voltages don't vary.

    A semi/non functioning neutral forces the legs to try to balance directly to each other - and the various random circuit balance points are why the individual circuit's voltages vary up and down.

    On the other hand; what the hell do I know? <g>

    PHM
    --------




    Quote Originally Posted by Poodle Head Mikey View Post
    Would a open / high resistance neutral out in the building do that? Cause one circuit to bright/dim another circuit?

    I would be looking back at the panel and before it. The bright/dim thing happens because of the two legs in the panel becoming unbalanced - more circuits active on one of the incoming legs than on the other incoming leg - with a non-semi functioning neutral to provide a balance so the circuit voltages don't vary.

    On the other hand; what the hell do I know? <g>

    PHM
    --------
    PHM
    --------
    The conventional view serves to protect us from the painful job of Thinking

  5. #4
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    It's not at the panel. I wish! It's in one of who know how many boxes in between. I once had a guy show me a cool trick to track down a bad hot connection that I tried once. Run some wire from the same breaker to one of the devices that are not working. Now you are feeding from both ends. Whatever in between is still not working is where your bad hot connection is. I was wondering if you could do the same thing with a neutral.

  6. #5
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    In my career, I've only seen a bad neutral in two places.

    The first was a good sized building that tested some sort of computer stuff that ran on 120V. Hundreds, maybe thousands of these things. The place needed a neutral about three times the size of normal.

    The other place is/was convenience stores. They scab in anything anywhere. Always using an existing neutral when putting in a new breaker.

    In the first case, an electrical engineer needed to be brought in. In the second case, you just check voltage on start at the unit and breaker. If the voltage drops below 10% at the unit, then check at the breaker. Most likely it won't drop that much. After that, it becomes, which is it, the hot or the neutral?

    You could just run a wire in the open air to a good neutral, then coil it back up again when through troubleshooting. But in my experience, I would just usually do something stupid like use a drain pipe as the source for my neutral, for testing purposes only.
    I do a triple evac with nitro to remove non condensables.

  7. #6
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    I am not an NEC Code Guy - but sure; why not? And for that matter: run a new neutral into the far end of the circuit and leave it in place. So long as it's back to the panel - what's the harm? I have a power circuit "fixed" that way in the house I am sitting in. I just ran a wire (actually 2/3 <g>) from the same breaker out to the farthest end of the string.

    But I want to go back to the idea that if it ain't the panel - it is Before the panel. Might have to get The Really Smart Guy sparkies here in on that one - but I don't think a single circuit with a bad neutral can imbalance voltages. A high resistance single circuit neutral could dim lights - but not brighten them.

    PHM
    -------


    Quote Originally Posted by Glennhvac View Post
    It's not at the panel. I wish! It's in one of who know how many boxes in between. I once had a guy show me a cool trick to track down a bad hot connection that I tried once. Run some wire from the same breaker to one of the devices that are not working. Now you are feeding from both ends. Whatever in between is still not working is where your bad hot connection is. I was wondering if you could do the same thing with a neutral.
    PHM
    --------
    The conventional view serves to protect us from the painful job of Thinking

  8. #7
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    Ok maybe I was not accurate in the dimming and Brightening. Maybe they were dim and went to normal depending on what switch was turned on. I just want you to steer away from the idea that the poor neutral was at or before the panel. I went back to the house a couple week later for his a/c check and he showed me the box behind the couch where they tracked it down finally. Whether it was a wire nut or at a receptacle terminal I do not know. Also there is a very likely possibility that two hots shared this neutral as was very common prior to the NEC change.

    Remember too that if it the service neutral the whole place is going to act strange not just one/two rooms.

    Wouldn't have needed a drain pipe, could have used the metal raceway here.

  9. #8
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    Its ALWAYS a back stabbed Rec .... or light switch .. or a Wire Nut melted down

    1 time was checking 6 recs that lost neutral ... all back stabbed ... along the line I pulled a Receptacle out and saw they did the hooks around the screw .. and I just let it hang there thinking .. naw thats not the one ... and kept checking back stabbed ones that shared the same line

    Gave up looking . Awe hell let me put everything back. Grabbed the Hooked receptacle and noticed 1 of the wires shifted ..hmm ... grab the screwdriver and turned the screw 1 whole turn in. wow

    Checked the power at the other Recs and the power was back to normal

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  11. #9
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    Try the trick with the neutral .


    Sent from my iPhone using Tapatalk

  12. #10
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    Quote Originally Posted by Glennhvac View Post

    Remember too that if it the service neutral the whole place is going to act strange not just one/two rooms.
    I didn’t think Mikey was referring to the service neutral. That said, I have found plenty of loose neutral circuit connections on the neutral bus bar in the main panel. So it wasn’t bad advise. I’m glad they found the loose connection. Shared wire junctions are a pain to locate when there are multiple junctions in a circuit that you’re not familiar with.
    "Quality is never an accident; it is always the result of intelligent effort. The bitterness of poor quality lingers long after the sweetness of low price is forgotten" --- John Ruskin

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    In the fun stuff column: Just was trying to suss out why some of the parking lot lamps are out. Guessing a neutral as there is "120VAC" across the wires servicing the four heads, but no light.

    Went to the breaker panel for the said lamps and in the process of identifying through the process of elimination, discovered that three poles (6 lights) had to have TWO double pole breakers on to get them to light! Opened a can of worms.... Will go fishing for the issues as the days go by...
    “A dying culture invariably exhibits personal rudeness. Bad manners. Lack of consideration for others in minor matters. A loss of politeness, of gentle manners, is more significant than is a riot.”
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  14. #12
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    Maybe you assumed they were 120v lights ... but are actually 220 ?

    Or ... the double pole breakers are wired to service 2 different lines of 120 .... but "share the neutral"

    When a customer surprises me with " hey while you're here can you add 2 separate outlets 120V real fast " and im in a hurry and don't have time to buy 12-2 , but I have 12-3 with me , I've been known to run 12-3 to a double pole , and since there is only 1 white wire it gets shared to serve both 120 outlets

    Perfectly legal , or it used to be atleast

  15. #13
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    USED to be.

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    IIRC, 2017 NEC allowed multibranch circuits to share a neutral IF a double pole breaker was used for providing the 2 hots.
    This assured that 240 vac was used to provide the 2 120vac circuits and the neutral would only carry the unbalance.

    This may have applied to 3 phase wye configuration also, requiring a 3 pole breaker and only one neutral.

    But now with GFCI and AFCI breakers this would not work out.

    Don't know about 2020 NEC, don't want to buy the book or even read it as it is getting close to closing time.

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