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78Volts only at main in house #204877
01/18/12 12:41 PM
01/18/12 12:41 PM
HappyElectrician  Offline OP
Joined: Dec 2011
Posts: 31
Penn USA
I have come across two homes in the past 3 weeks that have had the same problems.

At the main panel in the house I place my meter on the nuetral bar and one of the main feeders and I get 120v, then place the probe on the other main feeder and only get 78v. Of course leaving my probe on the nuetral bar and placing my other probe on the circuit wires I get 120v then 78v then 120v etc so as you can see it is one leg that is only delivering 78v. When I test the main feeders I place the probe directly on the feeder wire and not the main circuit breaker to be sure I am getting the actual reading from the incoming power by passint the main breaker.

At this point neithr customer has had me come back yet to actually fix it but this must be a problem with either the meter socket to the main panel, the main lines coming into the meter socket or the connection from the pole wires to the house wires. Yes, this means also that almost half the house is not functioning correctly because it is only getting 78v. Both houses are rental properties and the landlords have my proposals to fix the problems. Just seemed strange that I would get two of these exact same problems within 3 weeks.

Any thoughts on what else this could be.

Thanks for your input


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Re: 78Volts only at main in house [Re: HappyElectrician] #204880
01/18/12 02:19 PM
01/18/12 02:19 PM
wa2ise  Offline
Joined: Nov 2002
Posts: 786
Oradell NJ USA
Check the voltage from line to line. It's possible that the 78V side is being backfed thru electric water heaters and electric dryers (240V loads) from the side with the 120Vs. You'd see 120V-78V=42V, which would vary depending on how many light bulbs and such are turned on on the 78V side. But they should be complaining about a lack of hot water. And that the 78V side has a disconnected 120V up from the meter socket to on the power pole transformer or elsewhere in the POCO territory. Are the houses in the same neighborhood, fed by the same transformer?

Re: 78Volts only at main in house [Re: HappyElectrician] #204881
01/18/12 02:38 PM
01/18/12 02:38 PM
gfretwell  Offline

Joined: Jul 2004
Posts: 9,187
Trip the main breaker and look at the SE cable lugs. Check L/N and L/L.

With the service disconnect open you avoid back circuits from the other phase and the house loading down the connections back to the pole. If the voltage is nominal then, suspect a bad connections at the meter or back towards the pole. If you were dropping 32 volts in the main breaker or lugs, I would expect it to be pretty hot. If you have zero on the bad leg now, it is open back to the transformer

Greg Fretwell
Re: 78Volts only at main in house [Re: gfretwell] #204887
01/18/12 10:36 PM
01/18/12 10:36 PM
sparky  Offline
Joined: Oct 2000
Posts: 5,349
what they said

dibs it's a bum noodle.....


Re: 78Volts only at main in house [Re: HappyElectrician] #204891
01/19/12 12:12 PM
01/19/12 12:12 PM
HappyElectrician  Offline OP
Joined: Dec 2011
Posts: 31
Penn USA
AH !! Some good thoughts here; thanks. Will try the suggestions and never thought of the hot water heater back feeding.

No, the homes are in different towns miles from each other.

Will also kill the main breaker and test. But like I said when I originally tested the mains coming in I tested from the main wires going into the breaker not the breaker itself; but this may go hand in hand with the back feed and the one leg may be dead.

Thanks for your help


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