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Old 11-02-2010, 12:24 PM   #1
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Main breaker test???

Is there a way to test the integrity of a main breaker? My entire house lights dim when a motor is started anywhere in the house. A so called electrician says my main breaker is at fault and should be replaced. This is an expensive detail, and I would like to test and verify the main needs replacing first. Any ideas? Thanks.
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Old 11-02-2010, 12:55 PM   #2
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This could be caused by voltage drop from an undersized power company transformer, a poor or loose connection or a number of other factors. Unless the breaker has a poor connection to the buss I would not think it is your main breaker. There are other more common causes that need to be ruled out first.
Answers based on the National Electrical Code. Local amendments may apply. Check with your local building officials.
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Old 11-02-2010, 01:16 PM   #3
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Measure the voltage across the main breaker terminals. It should be zero. If when a load starts up the voltage goes up across the terminals then you have a problem. If it stays at zero then the voltage loss is somewhere else.
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Old 11-02-2010, 01:18 PM   #4
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Jim is on the right track. If the "whole house" lights dim when a Motor STARTS....(if I were working (retired) I would connect a recording volt meter ahead of the Main CB. In my many years of working I have found few MAIN CBs that were bad. Have found some that would not reset after opening them. That is after 30 to 40 years of NEVER exercising (opening and closing them). (just a side note)
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