# Voltage difference between two legs of service entrance

Performed an inspection today on a home built in 2001. Typical electrical service panels (two), however, when I was measuring voltage at the circuit breakers, I noticed a voltage difference of approximately 10 VAC between the two legs of the incoming power. When measured directly at the incoming lines, one leg measured approximately 113 VAC while the other was closer to 123 VAC. In addition, the interior lights flickered slightly when electrical demands (i.e. A/C system start-up, operating the trash compactor) were placed on the system. I typically only see 1-2 VAC difference between the two legs when measuring. Any ideas on why such a difference in the voltage…and comments on what (if any) deficiency?

Thanks,

Carey

There’s a bad connection at the point of attachment or the pole. The house has no neutral or a really bad neutral connection. Tell them to call utility to fix it. I go these calls all day long it’s a quick fix. But if they don’t there appliances will fail faster.

The problem is not necessarily at the utility connections. It can be in the panel if it affects the whole house or a loose circuit neutral if only one circuit is affected.

Both panels had the same readings and every other circuit breaker had low voltage…all circuits of the one entrance leg are affected with the low voltage.

Call it out, refer and move on.

Just curious, did you measure the voltages to ground, N and phases to phase? What were those voltage readings?

A-B=
A-N=
A-G=
B-N=
B-G=

A-B= ~236
A-N= ~113
A-G= ~113
B-N= ~123
B-G= ~123

When you reference “G” (ground), I was using the ground bus bar in the panel and likewise when measuring between “N” (neutral), I was using the neutral bus bar in the panel. When I measured continuity between both bus bars (ground to neutral) and between each bus bar and the panel enclosure I got less than one ohm for each measurement.

Since you’ve determined that the EGC bus was properly connected to the neutral bus then those voltage reading would be expected. There could be many reasons why there’s 10 volts of difference.

What kind of grounding eletrode system is being used? Is there a metallic water pipe electrode connected to a common city water supply?

I have had a whole new 200 amp panel installed and at times have had a difference of 121 on one leg and 118 on the other. Normally 121 one both

From an inspection and report writing point of view. I agree with you Roy.

From a purely educational point of view, there are several possibilities. The fact that the Voltage between the phase legs is 236 Volts, which is also the total Voltage of the two legs measured in reference to ground, suggests that the difference is most likely attributable either to total loading on the transformer or some of the windings on the transformer secondary have shorted. It is possible for several windings to short out with the transformer remaining operational, effectively changing the transformer winding ratio.

But you might find this as I did yesterday:

HVAC Inspector had an issue at the unit.

I found the main which also showed up at the HVAC sub pnl.