Residential voltage

[odu]

Measuring 120 on one side and 122 on the other..When most appliances are turned on the 122 increases to 124 and there seems to be some current transfer through the neutral/ground.

Does this sound like a transformer issue or a incorrect wiring issue in the home?

 

[busbar]

Without reading currents, it's hard to tell. In simple terms, expect a voltage range of ~110-126 volts.

 

[peebee]

Please provide a bit more information if possible. . . .

You mention you're reading L1/L2 voltages of 120/122 volts unloaded (I assume unloaded - verify).

When loaded, you are getting voltages of ???/124. I suspect the ??? side is seeing a voltage dip, please verify.

If ??? is seeing a voltage dip, it's possible you have a bad neutral-ground bond.

If the ??? side is instead rising in voltage, something very strange is going on -- it would sound almost like a leading power factor situation, which would be unusual in a residential installation.

Either way, please be more specific regarding voltage and current readings on each line, and provide some additional detail regarding the appliances you're turning on. Also please verify this is a 120/240v, 3ph. 4w+gnd system.

 

[odu]

Thanks....let me gather more info...it will be a week or so.

 

[Lewish]

I can think of at least one condition which would do this, with everything being normal. If all of your appliance load is on the same side of neutal, that side will droop in voltage and the other side will rise. This will be worse if the wire from the street to the house is quite small. I once had a house, which was built about 1920, which only had 75Amp service. I had a problem like this, but my voltages were farther apart. The power company replaced the drop with 200Amp service and the problem went away.

 

[peebee]

A broken neutral wire can cause extreme deviations between neutral and ground; in the worst case, one side will see nearly 240 volts and the other side close to zero. With an unreferenced neutral, the only return path is the loads on the other line; the voltage will be split in proportion to the loads on each side. This can be bad enough to lead to smoked insulation. A missing neutral-ground bond can have a similar effect, although usually much less extreme; broken N-G is usually more of a safety problem than an operational problem.

A solid neutral-ground bond will help "center" the neutral voltage at zero volts. Even then, though, if the neutral wires are not sized large enough and there is a large imbalance from L1 to L2, the resulting high neutral current will lead to a voltage drop as seen from the heavily loaded side and a voltage increase from the lightly loaded size. Balancing the loads from L1 to L2 will minimize the neutral current and help fix the problem. Increasing the size of the neutral conductor will also help -- this is essentially what fixed Lewish's problem.

 

[callaghan]

The City of Pasadena went through and rewired all residences from 120-0 to 120-0-120 many years ago. The problem was that they fused the neutral with the same size fuse as the hot leads, and when the neutral fuse blew, a number of appliances were destroyed. I bought a Pasadena house in 1974, and one of the first things I did was to bypass that fuse. (The house had a 30 amp service entrance,
with screw fuses in the mains)

 

[jghrist]

If one leg of the 120/240 volt service is loaded a lot more than the other, you should expect the heavily loaded side to have a voltage decrease and the lightly loaded side to have a voltage increase. This is because the voltage drop in the neutral, which carries the unbalanced current, will decrease the voltage on one leg but increase it on the other.

If the highly loaded leg current is within the rating of all of the equipment and conductors, and if the voltage is within the acceptable range (114-126 volts), you should be OK. Balancing the loads will result in better voltage regulation and lower losses, however.