Bad Netural

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Robbie Miller

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Location
Myrtle Beach SC
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Electrician
I have a home that homeowner that unplugged their dryer and when they did is sparked and some 120V receptacles had smoke coming out. I turned the power off to the dryer when I got there and pulled the receptacle out as I removed the receptacle it sparked and started smoking. Now all of the 220v appliances are fried along with some 120V. Everything reads proper voltage at this time. I have nothing that is 220v to put a load on the system and check it. The power company can't find any issues on their side. Ideas of suggestions?
 
120V receptacles don't smoke when they get hit w 240V, whatever is plugged into them is what gets smoked.

What do you mean "everything reads proper voltage"? Where are you reading voltage? Under what condition? If you have a bad neutral you would read something like 150V on one leg to neutral and 90V on the other.
 
It would be rare that an open neutral would damage line to line connected equipment, but could damage the controls in that equipment if the control power is line to neutral.
Turn off all of the branch breakers and measure the line to line and line to neutral voltages on both legs.
Disconnect a wire from a breaker on one leg and make a temporary connection to a large load such as a plug in heater. Measure the voltages again.
Move that load to a breaker on the other leg of the system and repeat the measurements.
A significant variation in the line to neutral voltages indicates a problem with the neutral on the line side of where you are taking the voltage readings.
You could ask the utility if they have a "beast of burden" tester and to use that to do the same thing. That plugs in at the meter and detects any neutral problems at the meter or on the line side of the meter.
 
ActionDave said:
120V receptacles don't smoke when they get hit w 240V, whatever is plugged into them is what gets smoked.

What do you mean "everything reads proper voltage"? Where are you reading voltage? Under what condition? If you have a bad neutral you would read something like 150V on one leg to neutral and 90V on the other.
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The abnormal line to neutral readings typically only exist when there is a load. With all of the loads off, the readings will most often look correct.
 
Sounding sort of like something I encountered one time, it was a mobile or manufactured home, they unplugged the dryer and several 120 volt items got smoked, but not unutilized receptacles as OP was describing and that is pretty unlikely and a misunderstanding maybe. Was caused by a lost feeder neutral in combination with bonding jumper not being removed in the dryer. That bonding jumper was carrying all the neutral current for the house back to the service equipment via the EGC, unplugging the dryer interrupted that non intended neutral path.
 
1st thing, don’t believe the utility guy! Too many of them don’t invest the effort they should, to find the problem.
 
Also, check for current on the cable tv and phone lines where they are bonded to the main
 
Robbie Miller said:
I have a home that homeowner that unplugged their dryer and when they did is sparked and some 120V receptacles had smoke coming out. I turned the power off to the dryer when I got there and pulled the receptacle out as I removed the receptacle it sparked and started smoking. Now all of the 220v appliances are fried along with some 120V. Everything reads proper voltage at this time. I have nothing that is 220v to put a load on the system and check it. The power company can't find any issues on their side. Ideas of suggestions?
Click to expand...
Is any of it MWBC?
Was the dryer running when it was unplugged?
How many recepts went smoking?
What 220v appliances?
What 120v appliances?
Do all the appliances have electronic controls?
And black/burn on the recepts?

Maybe dryer did very high voltage spike from inductive motor and when it was unplugged it went "zap"? Not sure why any recepts would be smoking though.

It sounds weird.
 
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