The Electrical Contractor Network

ECN Electrical Forum
Discussion Forums for Electricians, Inspectors and Related Professionals

Books, Tools and Test Equipment for Electrical and Construction Trades

Register Now!

Register Now!

We want your input!


2017 NEC and Related
2017 NEC
Now Available!

Recent Posts
International Wire Colour Codes
by Tjia1981
Today at 12:08 PM
Parking lot pole light swap....
by HotLine1
Today at 09:39 AM
Son of Sparky
by HotLine1
10/20/16 07:43 PM
Speaking of Plugmold ...
by gfretwell
10/17/16 02:37 PM
Broken battery charger? Check for cobwebs!
by gfretwell
10/17/16 02:30 PM
New in the Gallery:
12.5A through 0.75mm˛ flex (just out of curiosity)
Shout Box

Top Posters (30 Days)
gfretwell 12
HotLine1 7
renosteinke 6
ghost307 5
Potseal 4
Who's Online
0 registered (), 244 Guests and 4 Spiders online.
Key: Admin, Global Mod, Mod
Topic Options
Rate This Topic
#204877 - 01/18/12 08:41 AM 78Volts only at main in house
HappyElectrician Offline

Registered: 12/27/11
Posts: 31
Loc: 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


Work Gear for Electricians and the Trades

Work Gear for Electricians and the Trades
Work Gear for Electricians and the Trades
Arc Flash Clothing, Gloves, KneePads, Tool Belts, Pouches, Tool Carriers, etc. etc....

#204880 - 01/18/12 10:19 AM Re: 78Volts only at main in house [Re: HappyElectrician]
wa2ise Offline

Registered: 11/29/02
Posts: 769
Loc: 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?

#204881 - 01/18/12 10:38 AM Re: 78Volts only at main in house [Re: HappyElectrician]
gfretwell Offline


Registered: 07/20/04
Posts: 9024
Loc: Estero,Fl,usa
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

#204887 - 01/18/12 06:36 PM Re: 78Volts only at main in house [Re: gfretwell]
sparky Offline

Registered: 10/18/00
Posts: 5545
what they said

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


#204891 - 01/19/12 08:12 AM Re: 78Volts only at main in house [Re: HappyElectrician]
HappyElectrician Offline

Registered: 12/27/11
Posts: 31
Loc: 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


ECN Electrical Forums - sponsored by Electrical Contractor Network - Electrical and Code Related Discussion for Electrical Contractors, Electricians, Inspectors, Instructors, Engineers and other related Professionals