Different voltage on different circuits

Old 07-06-03, 02:55 PM
Visiting Guest
Posts: n/a
Different voltage on different circuits

What would cause some circuits to test 129-130v and some circuits to test 105-106v?
Old 07-06-03, 03:01 PM
Visiting Guest
Posts: n/a
There are two incoming hot wires in a residential service. Possibly, the receps that read 130 are on one leg and the ones that read 105 are on the other.
Old 07-06-03, 04:41 PM
Visiting Guest
Posts: n/a
Just wondering if this is normal. I would think that they should all be around 115-125v. I have one circuit that my coffeemaker is on that reads 106v until I turn on the coffemaker and then it jumps to 130v. The coffeemaker is new so I'm sure that's not the problem there. This one has me puzzled. Thanks for any help.
Old 07-06-03, 04:57 PM
Kooter's Avatar
Banned. Rule And/Or Policy Violation
Join Date: Jan 2003
Posts: 861
Received 88 Upvotes on 81 Posts
I'd say you have a bad neutral connection. The bad connection basically adds resistance or impedance to the neutral path. In a single-phase residential system, the voltage across the two "legs" of the system is 240 volts, which is used for loads such as ranges and clothes dryers. The receptacle for your coffe maker in this case is a 120-volt load, which ia arrived at by the neutral and one of the two hot legs. A loose neutral connection introduces a resistance in the neutral (or return path for the current) of both legs. Normally, when the current in leg 1 is greater than the current in leg 2, the voltages between the neutral and either leg are equal because there is no significant voltage drop at the neutral connection. In this case, when your coffe maker is operated, the current in that leg increases substantially more than the current in the other leg.

This unbalanced current causes a significant voltage drop (probably as much as 8 volts) across the neutral connection, which in turn causes the voltage across loads as well as your lights (on the same leg) to decrease. This decrease in voltage on one leg causes an increase in voltage on the "other leg", sometimes causing the lights on that leg to get brighter. Have you noticed any of your incandescent lights dim when other loads are used?

The bottom line is that I believe you have a bad neutral connection.

Old 07-06-03, 04:59 PM
Join Date: Sep 2000
Location: United States
Posts: 17,733
Upvotes: 0
Received 1 Upvote on 1 Post
Are you testing all "live" receptacles? It doesn't count if you test a receptacle that is controlled by a switch and the switch is off.

I encourage you to further explore hotarc's observation. See if you can identify which circuits read 105 and which read 130. If you can identify the pattern, we can speculate better. Post back with the circuit numbers (the number embossed in the panel cover) for the circuits reading 105, and also for the circuits reading 130.
Old 07-07-03, 07:32 AM
Join Date: Jan 2002
Location: Chicago
Posts: 1,860
Upvotes: 0
Received 0 Upvotes on 0 Posts
It may also be that the circuits with the lower voltage are already loaded (perhaps a fridge or other applicance is running while you were reading the voltage). That will cause a voltage drop on that leg, but not on the other perhaps.

Thread Tools
Search this Thread
Ask a Question
Question Title:
Your question will be posted in: