Loose neutral meltdown

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Old 02-24-04, 06:10 PM
Wiggllit
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Loose neutral meltdown

I had a sub-panel installed by a registered electrician in July. He put in a larger wire from the box at the meter too. In January after the tenant moved in the lights went out, the furnace blew a fuse, her two clocks stopped and the surge protector smelled like burned plastic. Oh yea, and my refrigerator stopped working.
I opened the circuit breaker box and saw melted wire insulation on the wires connected to the neutral buss and the plastic frame that held it was black, melted and drooping. I turned off the power at the meter and came back to find the large white wire was just laying in the hole, it wasn't screwed down!
I took it out of that hole and put it in another one because the screw for the old one was soft and broke off when I tried to tighten it. I wanted to get her heat on.
When the electrician finally came and replaced the damaged parts, he said it was caused by something else and charged me for parts and a service call.
What else could cause such an increase in current? And if he just made it the way it was supposed to be, won't it happen again according to his logic?
 
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Old 02-24-04, 08:02 PM
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I suspect that the cause of the problem was a loose connection. Recently I had a problem with the breakers tripping on a large electric heater. I used a non contact infrared thermometer to measure the temperature of the contact where the wires are connected to the breaker. When the heater was turned on the temperature quickly climbed to between 250 and 300 degrees. After the power was turned off at the main breaker I tightened up on the connection screws only about one quarter of a turn. That made all the difference. Temperatures fell to about 75 and held steady. I've seen loose connections on wires that carry a reasonable amount of current get melted and/or badly burned many times. It almost always is due to a connection that isn't tight enough. Your electrical guy didn't get the connections tight enough when he did the work. That's why the neutral wire melted. Your electrical guy probably recognized his mistake by what he saw and did things right the second time. If that's the case you probably won't have any further problems. Your electrical guy probably is hoping you won't find out that he screwed up. It's an easy (but can be expensive) mistake to make. At least that's the way I see it with the info you've provided.
 
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Old 02-24-04, 08:05 PM
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The neutral of a single phase residential service is a connection to the center tap of the transformer on the pole. It is essentially a reference point for the 120 volts of each leg to go to. If it is removed, there is no neutral return and the voltage has to divide proportionally accross whatever loads the two legs are connected to.
For example, you have a 120 watt light on one leg and a 1200 watt hair dryer on the other leg. The light has 10 times the impedance that the dryer does. When there is is no neutral reference point, the voltage will split proportionally across the impedances (Ohms Law). So the light will have 10 times more voltage drop across it than the dryer does.

Poof!

Your electrician didn't want to admit his mistake.
 
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