I got a call from a customer this past week. He said he was having issues with the electrical in his summer cottage. I went there today to check it out. I checked the voltage on the 2 main breaker lugs and got 220V. When I tested leg to ECG i got 236V on 1 leg and around 60V on the other leg. I turned all the breakers off and recheck voltage and got a perfect 110/110 on each leg. Only when I apply a load does the voltage seem to get screwed up. I have seen this happen when a neutral is lost from PoCo. How would I be able to tell if the problem is on the utility side of the equipment?
Strange voltage readings
- Thread starter Dansos
- Start date
- Status
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
Definitely a bad neutral. To find it, you have to work your way toward the source (while under load so the imbalance shows) until you reach the point where the voltages match, including both sides of the meter.
ptonsparky
Tom
- Occupation
- EC - retired
As Larry says. We disconnect all the electronics and plug in a hairdryer or portable electric heater for the load.
- Location
- Tennessee NEC:2017
- Occupation
- Semi-Retired Electrician
I hope you were just giving general (in the neighborhood) voltage readings because what you listed does not sound right. First, you should have more than 110V on each leg. It might not be 120V but is usually somewhere between 117V-121V. If you measured 236V on one leg, and the neutral was lost/open, you would have less than 60V on the other. You also might be reading phantom voltage on a digital meter if you got 60V.
To answer your question, since you have already checked the line side of the main, you would have to pull the meter (or have the POCO pull it) and check the connections in there, both line and load, including the neutral connections. This will tell you if it's on the customer side or POCO side.
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
181026-2402 EDT
Dansos:
Good on line to line of 220, probably both loaded and unloaded, then 110 from each line to neutral when unloaded. I assume your measurement to EGC also was really equivalent to neutral.
When you applied load, then you read 60 V from one line to neutral, and 236 from the other line to neutral. I assume there is a low impedance between the neutral and EGC bus bars in the main panel.
If I square 236 it equals 55,696, and squaring 60 it equals 3600. Add the two squared values (right triangle assumption), and take the sq-root the result is 244 V. This is higher than your 220. I would have expected a better correlation. Adding 236 and 60 = 296, as if the load was all resistive, which is way above 220. So I made the assumption of an inductor in series with a resistor to do the right triangle calculation.
Almost certainly you have an open neutral as others have said.
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Dansos:
Good on line to line of 220, probably both loaded and unloaded, then 110 from each line to neutral when unloaded. I assume your measurement to EGC also was really equivalent to neutral.
When you applied load, then you read 60 V from one line to neutral, and 236 from the other line to neutral. I assume there is a low impedance between the neutral and EGC bus bars in the main panel.
If I square 236 it equals 55,696, and squaring 60 it equals 3600. Add the two squared values (right triangle assumption), and take the sq-root the result is 244 V. This is higher than your 220. I would have expected a better correlation. Adding 236 and 60 = 296, as if the load was all resistive, which is way above 220. So I made the assumption of an inductor in series with a resistor to do the right triangle calculation.
Almost certainly you have an open neutral as others have said.
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