240 volts from Neutral to hot residential...?

[powerplay]

How would someone read 240 volts from breaker to neutral on a single phase residential panel? The power authority came and checked the street connection which they said was ok, but apparently when certain breakers are on in the panel, their meter reads 240 volts from breaker to neutral in the panel...

 

[G._S._Ohm]

The neutral on those breakers goes to the other 240v lead through a load or through a wire?
Depending on what you used to measure it, it could be a phantom voltage.
Did it ruin the 120v appliances?

 

[powerplay]

The neutral on those breakers goes to the other 240v lead through a load or through a wire?
Depending on what you used to measure it, it could be a phantom voltage.
Did it ruin the 120v appliances?

It was a phone question..rather hard to troubleshoot. I think he used a solenoid tester. It may be user problem....

 

[ptonsparky]

Just because the street connection is good doesn't mean that there is not a failure of some sort between there and where the voltage checks are made. Open neutral is first thought. Pretty unusual for a full 240 but possible

 

[gar]

121111-2113 EST

powerplay:

You need a good meter, such as a Fluke 27, and a roughly 1 kW heater load.

Now you need to make some voltage measurements. Hopefully you can go to the utility transformer pole and connect to or close to its ground rod. The pole ground rod should be a good connection to the center tap of the transformer. Run a wire from this ground rod back to the main panel area to serve as a long test lead. Even #24 wire would work because it is only a voltage reference to the meter. But be careful. Because if something is really wrong at the power company side of the house there could be a high voltage potential across the earth from one point to another. You could put a screwdriver in the ground next to the ground rod as a means of getting this voltage reference as we expect very little current to flow thru this ground rod.

Before going in the house measure the voltage from the pole ground rod to the house ground rod. Probably should be less than 1 volt. Also visually check that the wire and connections from the house ground rod to the main panel look good.

In the house measure the voltage from the pole ground rod to each 120 V phase. These should be approximately equal voltages with any combination of breakers open or closed.

These results will determine the next measurements. Later you will use the 1 kW load.

.

 

[G._S._Ohm]

With a gross fault like this I'd think almost any meter or a 240v incand. test lamp would work. This problem ain't too subtle.

 

[n1ist]

Possibly an open neutral and a rather low impedance load from one phase to neutral. Neutral to the other phase will be close to 240.
/mike

 

[powerplay]

Just because the street connection is good doesn't mean that there is not a failure of some sort between there and where the voltage checks are made. Open neutral is first thought. Pretty unusual for a full 240 but possible

..I should have said connection to meter base was good...

 

[powerplay]

121111-2113 EST



In the house measure the voltage from the pole ground rod to each 120 V phase. These should be approximately equal voltages with any combination of breakers open or closed.

These results will determine the next measurements. Later you will use the 1 kW load.

.

He shut off the Main breaker to isolate panel and and found proper readings from the Line side of panel. I mentioned to use a good meter, and to make sure he isn't seeing 240mV.

With certain breakers off, the readings are ok, but with certain breakers closed..the readings change. Series circuit somewhere, but 240volts from neutral to one phase?

 

[gar]

121112-1-11 EST

powerplay:

With the main breaker open there is no load on the line side. Thus, no current. A high impedance meter will probably read correct voltages to neutral even with an open neutral somewhere between the power company transformer and the input side of the main breaker. Now you need a low resistance load across the meter. The 1 kW heater or even a 100 W incandescent bulb is likely to produce a noticeable voltage difference from the no load value.

.

 

[suemarkp]

All you need is a ratio of 100:1 in load resistance between phase legs and an open neutral. So if one leg has a device that draws 100ma and the other leg has a device that draws 10A, you'll get 239V across the 100ma device and 1V across the 10A device. Hopefully the 100mA device doesn't fry when it sees a 239V source voltage...