Unbalanced service

[102 Inspector]

As an inspector, I reviewed and approved an electric meter installation as 200 Amp overhead service. Typical installation with panel directly behind meter inside the dwelling under construction. Phase conductors properly landed in panel and meter base, grounded conductor properly landed and grounding completed by 2 ground rods. Bonding screw properly installed. Electrician called this morning and indicated he was getting readings of 120 V on one phase and 208 on the second phase which apparently burned out a circuit board on a furnace. Phase to Phase he said was 240 V. It sounded like a grounded conductor (neutral) was lost, but I always thought that in that case the total of each phase would add up to the 240V expected. Why would one phase show 208V. Trying to learn, not blame.

 

[jim dungar]

As an inspector, I reviewed and approved an electric meter installation as 200 Amp overhead service. Typical installation with panel directly behind meter inside the dwelling under construction. Phase conductors properly landed in panel and meter base, grounded conductor properly landed and grounding completed by 2 ground rods. Bonding screw properly installed. Electrician called this morning and indicated he was getting readings of 120 V on one phase and 208 on the second phase which apparently burned out a circuit board on a furnace. Phase to Phase he said was 240 V. It sounded like a grounded conductor (neutral) was lost, but I always thought that in that case the total of each phase would add up to the 240V expected. Why would one phase show 208V. Trying to learn, not blame.

Voltage readings are not helpful without knowing the reference points used for the measurement, and if they were made at the same time, as changes in the loading can impact the voltages when the neutral is lost.

But in this situation, it sounds like the service is actually a 240/120V 3-phase 4 wire. And connection was made using the "B" instead of the "A and C" phases. These are also called high-leg, wild-leg, and a few other terms. If installed per the NEC the voltages you could expect are:
L1-L2 = 240V
L2-L3 = 240V
L3-L1 = 240V
L1-N = 120V
L2-N = 208V
L3-N = 120V.

 

[Fred B]

As an inspector, I reviewed and approved an electric meter installation as 200 Amp overhead service. Typical installation with panel directly behind meter inside the dwelling under construction. Phase conductors properly landed in panel and meter base, grounded conductor properly landed and grounding completed by 2 ground rods. Bonding screw properly installed. Electrician called this morning and indicated he was getting readings of 120 V on one phase and 208 on the second phase which apparently burned out a circuit board on a furnace. Phase to Phase he said was 240 V. It sounded like a grounded conductor (neutral) was lost, but I always thought that in that case the total of each phase would add up to the 240V expected. Why would one phase show 208V. Trying to learn, not blame.

Any repairs on the system prior to failure?
Sounds like a POCO mistake connecting the wild leg onto a 120/240 system. Or if was suppose to be a 240/120 Delta POCO changed position of wild leg. A dropped Neutral with other loads will create a variable high and lows on phase conductor to N/G. Or someone Moved the breakers on a wild leg system.
Seen Power outage that POCO connected up wrong or was provided the wrong xfer for a repair.

 

[102 Inspector]

This is a single phase, 120/240V 3 wire service, typical residential drop. There is no transformer on the pole and I am not aware of any 3 phase in the area. The test point were phase to neutral and phase to phase from what the electrician told me. I agree it sounds like a 3 phase service, but it is not intended to be unless the POCO has wiring I am not aware of on the pole. Again, trying to learn why the differences in readings. Everything a result of a phone conversation, no actual readings conducted by me. Thank you

 

[LarryFine]

Are there other customers on the same secondary where you can make test measurements?

It should be impossible to receive 120v and 208v simultaneously; the 208v specifically is weirder.

 

[Fred B]

Open neutral will cause a variation of L/N voltages depending on loads at the time of measurement. If no alterations to system by anyone then likely a dropped neutral. Could be at pole, the meter, service point, any where back to the transformer. If no other issues with neighbors like limited to customer connections point. Turning off all breakers would give you near zero on both L/N other than what would be allowed via the GE connections, shouldn't be much, could be a little elevated if multiple residences ties to a common water line. Then the neighbors would be suffering from elevated NEV caused by your dropped neutral.

 

[retirede]

If there was a significant change in loads between the time he took the 2 measurements……..heck of a coincidence if he took one measurement immediately after the other.

I would plug in a space heater to the side he measured 120V on and recheck. If it a bad neutral, the voltage should drop significantly.

 

[102 Inspector]

As an update, I have been informed that the problem has been corrected and told it was a POCO neutral issue. Still trying to figure out if the electrician was not reading meter correctly or how he got 208 on one phase. Thanks for all the comments.

 

[kwired]

Open neutral will cause a variation of L/N voltages depending on loads at the time of measurement. If no alterations to system by anyone then likely a dropped neutral. Could be at pole, the meter, service point, any where back to the transformer. If no other issues with neighbors like limited to customer connections point. Turning off all breakers would give you near zero on both L/N other than what would be allowed via the GE connections, shouldn't be much, could be a little elevated if multiple residences ties to a common water line. Then the neighbors would be suffering from elevated NEV caused by your dropped neutral.

If it is an open neutral situation if you have 208 on one line then the other should read about 32 volts.

Still sounds like the source ultimately comes from a high leg delta somewhere and POCO screwed up making connections.

 

[kwired]

As an update, I have been informed that the problem has been corrected and told it was a POCO neutral issue. Still trying to figure out if the electrician was not reading meter correctly or how he got 208 on one phase. Thanks for all the comments.

About had to involve other customers? If bad neutral to the one customer only voltage should been like I said in the other post 208 one line to neutral and 32 on the other.

 

[Strathead]

As an update, I have been informed that the problem has been corrected and told it was a POCO neutral issue. Still trying to figure out if the electrician was not reading meter correctly or how he got 208 on one phase. Thanks for all the comments.

I would bet that smart guy Jim gave you the right answer at the very beginning of the thread. The voltages are too perfect to be anything else. The POCO just gave a simple explanation while still taking responsibility. No harm no foul.

 

[Fred B]

If it is an open neutral situation if you have 208 on one line then the other should read about 32 volts.

Still sounds like the source ultimately comes from a high leg delta somewhere and POCO screwed up making connections.

Maybe, but depending on what is on at the given moment a reading was done you can have "Odd" readings, large 1P load comes on while metering etc. Have had just such sort of thing as loads came on and off the readings fluctuated so much it was difficult to get a solid number for either leg. Shutting off all multipole loads and reading ahead of such should give a solid LL 240 and LN 0, or nearly, with a dropped neutral. Method of testing not given from OP as to whether Loads were present at time of testing.
Not to rule out a POCO error, seen it including erroneous high leg connection. But if no others on the transformer had issues more likely still a dropped neutral somewhere on the single feed to the residence. Either way, Overall it is safer (cost liability) for the POCO to claim a dropped neutral than to admit to error connecting to a high leg.

 

[kwired]

Maybe, but depending on what is on at the given moment a reading was done you can have "Odd" readings, large 1P load comes on while metering etc. Have had just such sort of thing as loads came on and off the readings fluctuated so much it was difficult to get a solid number for either leg. Shutting off all multipole loads and reading ahead of such should give a solid LL 240 and LN 0, or nearly, with a dropped neutral. Method of testing not given from OP as to whether Loads were present at time of testing.
Not to rule out a POCO error, seen it including erroneous high leg connection. But if no others on the transformer had issues more likely still a dropped neutral somewhere on the single feed to the residence. Either way, Overall it is safer (cost liability) for the POCO to claim a dropped neutral than to admit to error connecting to a high leg.

The POCO's here would not do that, but they are not for profit organizations either.

I had one on a cattle feeding operation one time that had a high leg delta that had underground primary that was aging. Load was minimal enough they started just operating it as open delta and if a primary line went bad they'd swap primary conductors to get it going and make the repair at their convenience on the bad underground. Probably was the last time it went bad that prompted them to replace all the underground with new a short time later. Their guys swapped lines and checked rotation but never verified high leg was in the correct position. I had quite a few things to repair, but POCO is who paid me to do so.