120v on neutral

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topend

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Hello. Last week I did a panel change, which included consolidating a 4 ckt sub-fusebox into the new loadcenter. I ran 2 - 12/3 RX to the fusebox and shared the neutrals. Everything was working when I left the job, now there is a dead short situation due to 120v on one of the existing knob&tube neutrals. Anybody have any ideas?

Thanks,
Rich
 
Was the 4 circuit fuse box 120 only before you worked on it? Is there a possibility of the "hot traveler" 3-way switch circuit? That was common in knob and tube systems.
 
Disconnect and isolate all the original K&T leads check continuity between everything. One hot lead should only have continuity to its corresponding neutral lead. Anything else is crossover and may have originally been that way but worked because things were on the right phase but now you have something on a different phase than what the crossed over item is on. It was not proper in the first place but worked with no apparent problems.

I don't know what you mean when you say you have 120 volts on the neutral. If you disconnect a neutral with live load connected to it you should have 120 volts to the source neutral. If it blows the fuse or breaker when you connect it you have a line to neutral short circuit someplace.
 
Not sure what a K&T three way is. Are you guys referring to a three-way switch, as in a lighting circuit? Like I said, the four neutral conductors were terminated on a common neutral bar.
@ kwired - In my experience, K&T conductors are not "paired" up when they enter the panel and never thought that it mattered which new neutral conductor the old ones were connected to. I do reckon that I have a line to neutral short, because I get 120v between this one particular neutral conductor and ground. Not sure I follow the phasing issue with just a hot and a neutral.
 
Just hung up with homeowner. Seems that the neighborhood has an inordinate number of "power surges". We have had alot of stormy weather in the past week... ?
 
topend said:
Not sure what a K&T three way is. Are you guys referring to a three-way switch, as in a lighting circuit? Like I said, the four neutral conductors were terminated on a common neutral bar.
@ kwired - In my experience, K&T conductors are not "paired" up when they enter the panel and never thought that it mattered which new neutral conductor the old ones were connected to. I do reckon that I have a line to neutral short, because I get 120v between this one particular neutral conductor and ground. Not sure I follow the phasing issue with just a hot and a neutral.
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K&T conductors are not necessarily "paired up" when entering a panel but if you have them disconnected and have continuity between more than one hot and/or more than one neutral you have crossover between multiple circuits someplace.

You can also have a crossover between two hot conductors someplace - probably was not intentional but it does happen. If both conductors are on same phase you never know you have a problem unless you discover you need to turn off more than one fuse or breaker to kill power to the circuit. Change the panel out and get the two on opposing phases and you now have a short circuit.

You can not have 120 volts between neutral and ground unless there is an open circuit between the neutral and ground conductors such as with a missing main bonding jumper. You can and will have small amounts of voltage between these two conductors if they are in good condition and there is load on the neutral, but a full 120 volts with everything connected and in good condition is not possible. If you have not taken anything apart when taking this reading you likely have an open neutral upstream of where you are taking the reading, or a line to ground short and no main bond on the EGC at its source.
 
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@kwired - what's got me scratching my head is that it worked for a week... Wiggy buzzed and jumped to 120v between K&T neutral and ground conductor in new RX from panel. Couldn't this be caused by a hot conductor shorting to that neutral downstream somewhere?
 
topend said:
@kwired - what's got me scratching my head is that it worked for a week... Wiggy buzzed and jumped to 120v between K&T neutral and ground conductor in new RX from panel. Couldn't this be caused by a hot conductor shorting to that neutral downstream somewhere?
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Yes but only if the neutral is open from the source otherwise you will still have fault level current flowing through it. If it is simply disconnected it will also read same with load connected in the circuit That neutral is not 'neutral' when it is disconnected.
 
draw1.jpg

Hopefully this drawing is large enough to see.

What would you expect a volt meter connected between points A and B to read if voltage applied to L1 and N is 120 volts? This is situation that I was talking about in previous post.
 
don_resqcapt19 said:
You would be reading though the load so you should see 120 votls.
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I agree. You created a MWBC and if one leg is still fed then you will see 120v to from neutral to ground. This is why a DP breaker is required in this situation or 2 sp breakers with handle ties.

It is probably coincidental that there is a problem but it sounds like you did other work so it would be hard to know for sure.

Also when you ran the 2- 12/3 to the panel did you tie all the neutrals together or did you arbitrarily choose 2 pair.

The problem with this is you could be overloading the neutral if the correct neutrals are not pair on different phases for their respective ungrounded conductors.
 
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Dennis Alwon said:
I agree. You created a MWBC and if one leg is still fed then you will see 120v to from neutral to ground. This is why a DP breaker is required in this situation or 2 sp breakers with handle ties.
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You will read the 120 between the points on the drawing even if this is not a multiwire circuit. The drawing shows an open neutral and he is placing his meter across the open in the neutral.
 
with my limited experience with k&t wiring, i've found that the "white" wire isn't allways the neutral, quite often it was sent down to the switch hot. i also like using a proximity tester over a wiggys when troubleshooting k&t. most that i have worked on it's nearly impossible to see which wire is white and which is black. making it difficult to tell whats what. good luck!
 
mgmelec said:
with my limited experience with k&t wiring, i've found that the "white" wire isn't allways the neutral, quite often it was sent down to the switch hot. i also like using a proximity tester over a wiggys when troubleshooting k&t. most that i have worked on it's nearly impossible to see which wire is white and which is black. making it difficult to tell whats what. good luck!
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I find it hard to tell which one is white too, especially when they are all black.
 
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