Ron Cole
Member
- Location
- Durham, NC, US
The reason I post this story is to perhaps find some answers to questions still pending:
I was called out to a single family dwelling by a realtor. He said the renters were watching television.... they heard a "pop" and the TV quit working. All the 240 appliances were not working. They also had no hot water.
When I first arrived, I went to find the Panel. On this house, on the outside, is a Zinsco combination Meterbase and Panel- with Main Lugs...with 6 double pole breakers. Indoor Sub Panel (QO) powered by 60 amp breaker fed from main box.
Homeowner thought we had a bad water heater breaker. First thing I did was get my meter out and take a reading between phases of the breaker. Read 240 volts. But when I read one phase and the neutral bus I also got 240 volts. And nothing on the other phase and neutral. I took the 2pole branch circuit, and moved it to a different breaker in the same panel (ie, switched between 2 30amp breakers). Meter read the same conditions. I took a reading at the main lugs. Meter also read 240volts across both phases, but the phases to neutral were unbalanced. Ie, approx 130volts (one phase to neutral) and 110volts (other phase to neutral).
Next, we unhooked the number 10 romex feeding the water heater. capped it off in midair, and took another reading. The 30amp breaker read (roughly) 120v from each leg to the neutral bus. Obviously, something was not right with the water heater.
We put that on hold, because I thought perhaps the 240volts on one leg may have backfed through the 60amp feeder, and caused damage in the house. As mentioned, the dryer, (and fridge) stove, etc. were not working. But lights were on in the house. We inserted a plug tester into a few different outlets in the house, which read normal. But when the homeowner turned on the toaster, all the lights in the house went out....! I read 38volts across one leg to ground, (on the 60amp main breaker of the QO panel) and nothing across the other, when the toaster was on. As soon as the toaster was turned off, all the lights came on again. Repeat the process, same results.
Went back outside to the Main Lugs. With the toaster turned on, I read the same voltages. Time to call Duke Power.
When the linesmen arrived, they had a record of a buried junction between the meterbase and the transformer behind the house. They dug up the junction... and just a few inches from this junction, the 4/0 Neutral Cable was badly corroded! From the picture, it looks like it was hanging on by one...maybe two strands. This explains the occurrences with the lights working, and the toaster drawing more than the feeder could handle. Actually, it explains almost everything... almost. Especially when the neutral was repaired and everything in the house got to working again except the television.
But what of the Water Heater? When examined, the lower element and both thermostats were burned up. But that does not explain getting a 240volt reading across one leg, does it? Water Heaters don't rely on a neutral. And I DID have a current carrying ground wire, when I touched the ground wire feeding the water heater... Ie, before we disconnected it. So this adds to the question list, doesn't it? Were these issues separate -ie the failed neutral and the water heater? If so, which symptom came first? And none of this explains to me how I was getting this 240volt reading from one leg of the WH breaker to ground. I've talked to 2 retired inspectors and a couple of plumbers. Only one of the four had ever seen 240v on one leg, and he says he thinks the water heater was leaking. But doesn't it still seem strange that we lost a neutral AND the water heater suffered so much damage?
And just in case I didn't explain enough, please let me know. Ask and I'll try to answer. The Zinsco panel had a main neutral/ground bus, and the Sub Panels were separated ground and neutral, as required by code.
I was called out to a single family dwelling by a realtor. He said the renters were watching television.... they heard a "pop" and the TV quit working. All the 240 appliances were not working. They also had no hot water.
When I first arrived, I went to find the Panel. On this house, on the outside, is a Zinsco combination Meterbase and Panel- with Main Lugs...with 6 double pole breakers. Indoor Sub Panel (QO) powered by 60 amp breaker fed from main box.
Homeowner thought we had a bad water heater breaker. First thing I did was get my meter out and take a reading between phases of the breaker. Read 240 volts. But when I read one phase and the neutral bus I also got 240 volts. And nothing on the other phase and neutral. I took the 2pole branch circuit, and moved it to a different breaker in the same panel (ie, switched between 2 30amp breakers). Meter read the same conditions. I took a reading at the main lugs. Meter also read 240volts across both phases, but the phases to neutral were unbalanced. Ie, approx 130volts (one phase to neutral) and 110volts (other phase to neutral).
Next, we unhooked the number 10 romex feeding the water heater. capped it off in midair, and took another reading. The 30amp breaker read (roughly) 120v from each leg to the neutral bus. Obviously, something was not right with the water heater.
We put that on hold, because I thought perhaps the 240volts on one leg may have backfed through the 60amp feeder, and caused damage in the house. As mentioned, the dryer, (and fridge) stove, etc. were not working. But lights were on in the house. We inserted a plug tester into a few different outlets in the house, which read normal. But when the homeowner turned on the toaster, all the lights in the house went out....! I read 38volts across one leg to ground, (on the 60amp main breaker of the QO panel) and nothing across the other, when the toaster was on. As soon as the toaster was turned off, all the lights came on again. Repeat the process, same results.
Went back outside to the Main Lugs. With the toaster turned on, I read the same voltages. Time to call Duke Power.
When the linesmen arrived, they had a record of a buried junction between the meterbase and the transformer behind the house. They dug up the junction... and just a few inches from this junction, the 4/0 Neutral Cable was badly corroded! From the picture, it looks like it was hanging on by one...maybe two strands. This explains the occurrences with the lights working, and the toaster drawing more than the feeder could handle. Actually, it explains almost everything... almost. Especially when the neutral was repaired and everything in the house got to working again except the television.
But what of the Water Heater? When examined, the lower element and both thermostats were burned up. But that does not explain getting a 240volt reading across one leg, does it? Water Heaters don't rely on a neutral. And I DID have a current carrying ground wire, when I touched the ground wire feeding the water heater... Ie, before we disconnected it. So this adds to the question list, doesn't it? Were these issues separate -ie the failed neutral and the water heater? If so, which symptom came first? And none of this explains to me how I was getting this 240volt reading from one leg of the WH breaker to ground. I've talked to 2 retired inspectors and a couple of plumbers. Only one of the four had ever seen 240v on one leg, and he says he thinks the water heater was leaking. But doesn't it still seem strange that we lost a neutral AND the water heater suffered so much damage?
And just in case I didn't explain enough, please let me know. Ask and I'll try to answer. The Zinsco panel had a main neutral/ground bus, and the Sub Panels were separated ground and neutral, as required by code.
