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#196226 - 09/19/10 11:43 PM tool to find open neutral in multiwire circuit
crselectric Offline
Member

Registered: 09/24/06
Posts: 134
Loc: albany, ca
found strange voltage to ground when trying to correct unbalanced panel wires, all four 3wire cables ran to main were all on same phases, guy used twins and put both bl. and red on same breaker. found one set giving me 68 volts red wire to phase a and 168volts to b, not sure of voltage to ground when both breakers off, only hooked up black wire, goes to fish tank and other wall plugs, could not find red wire, but didnt do exhuastive look, will do tomarrow, didnt want potential 240 across 120v gear. I figure that the white wire nut in a box finally burnt out with potential of 40amps coming back. I also got 1.81 ohms to neutral bar, so small load on red wire.....not alot of training in troubleshooting, and was stumped on friday thanks chris

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#196231 - 09/20/10 09:33 AM Re: tool to find open neutral in multiwire circuit [Re: crselectric]
crselectric Offline
Member

Registered: 09/24/06
Posts: 134
Loc: albany, ca
found tool, open circuit tracer. What I was wondering is what I should expect from a normally wired circuit? some amount of ohms on hot leg to ground bar? but only if I have a connected return? correct? or I might have a return faulted on egc?

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#196248 - 09/21/10 02:22 PM Re: tool to find open neutral in multiwire circuit [Re: crselectric]
wewire2 Offline
Member

Registered: 11/14/02
Posts: 246
Loc: California
Sounds like you lost a neutral connection. Trace the 3 wire to
the splice point and you should find a bad connection. Good idea
to disconnect the red until you find the problem!

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#196249 - 09/21/10 03:04 PM Re: tool to find open neutral in multiwire circuit [Re: wewire2]
gfretwell Offline

Member

Registered: 07/20/04
Posts: 9045
Loc: Estero,Fl,usa
WeWire has a good point on the red leg. Then put a load on the black leg beyond the failure (60w lamp) and look for the voltage drop. It will be the hot wirenut. A noncontact thermometer is great for things like this and now days the discount tool places have them for $30 or so. They are not a lab grade instrument but you can tell the difference between a good connection and a bad one. Real handy looking at breaker lugs in a panel.
_________________________
Greg Fretwell

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#196308 - 09/24/10 09:31 AM Re: tool to find open neutral in multiwire circuit [Re: gfretwell]
crselectric Offline
Member

Registered: 09/24/06
Posts: 134
Loc: albany, ca
went back on monday, my supervisor, tech. serv. dept.(permit and inspection coordinator) said all we're doing is disconnecting the hazard, disconnected the red lead at the first box and capped it, he was not interested in looking for anymore problems.....looks like the home owner might have run the cables, but said had someone else land the panel, as the romex in house is nice and neat, but the panel is a twisted mess?...the first box we found had 12/3 feeding 14/3, homeowner said he had larger wire installed for more capacity, I explained the need for putting the circuit on a 15amp breakers, and my super was going to come back with 15amp breakers, and this guy has a very well detailed house waiting to burndown......

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#196375 - 09/28/10 05:10 PM Re: tool to find open neutral in multiwire circuit [Re: crselectric]
Tesla Offline
Member

Registered: 06/16/04
Posts: 1280
Loc: Sacramento, CA
As I read the OP: guy used twins and put both bl. and red on same breaker...

Then ALL of the associated neutrals are overloaded. They've got 15A Black and 15 A Red out bound -- and 30 A coming back on white as they are from the same phase.

NO WONDER HE'S GOT TROUBLES.

The 'twins' split the OCPD -- but not the phase.

After correcting the neutral trouble...

Kill all of the breakers and shift the blacks and reds such that they hit alternate phases. Do this ASAP, before more damage is done. As it stands, your neutrals are being cooked.
_________________________
Tesla

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#196385 - 09/28/10 09:42 PM Re: tool to find open neutral in multiwire circuit [Re: Tesla]
crselectric Offline
Member

Registered: 09/24/06
Posts: 134
Loc: albany, ca
Yeah I did put the multiwire ckts on opposite phases, and isolated red on the suspect circuit. black phase seems to work ok, and thats all the HO wanted us to do so we would pass solar pv inspection. I did tell my boss(not an electrician} that the resulted short could still exist and that the HO should get it solved, but thats not in our scope......the previous guy did use scotchloks, not sure and I doubt they were installed properly......maybe I'll get the contract to rewire after his house fire?......CRS

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#196397 - 09/29/10 11:39 PM Re: tool to find open neutral in multiwire circuit [Re: crselectric]
Tesla Offline
Member

Registered: 06/16/04
Posts: 1280
Loc: Sacramento, CA
On the evidence, your wait may be short.

Anyone dumb enough to run multi-wire like that: just what else could they do?
_________________________
Tesla

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