How to test for voltage at the service panel

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  #1  
Old 06-23-11, 12:13 PM
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How to test for voltage at the service panel

Hi everyone,

I am preparing to install a few breakers to my service panel. The wiring has been run to the outlets and lights so I just have to connect the wires into the main panel. In my home, the mains come in and have a 100A main shutoff, from there it goes to a breaker box which houses all of the circuit breakers for the house.

My question is...If I shutoff the main breakers at the main breaker box, will the panel with all the individual breakers be "dead", including the main lugs in that panel. I have a multimeter and have used it to test outlets and switches, but have never used it to test power at the service panel and I am a little nervous to touch metal probes to those main lugs. With the multimeter set to test voltage where should I make contact with the probes to see if there is power coming into the subpanel/individual breaker panel?

I feel comfortable installing my new breakers with the mains shut off at the first box, but would feel much much more comfortable if I was able to confirm or deny with the multimeter if there was power to the mains at the second individual breaker panel.

Thanks for your help,
 
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Old 06-23-11, 12:27 PM
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Originally Posted by InNeedofHeat View Post
the mains come in and have a 100A main shutoff, from there it goes to a breaker box which houses all of the circuit breakers for the house.
If the breaker panel is separate from the main shutoff, then it is probably completely dead when the 100A main is turned off.

With the multimeter set to test voltage where should I make contact with the probes to see if there is power coming into the subpanel/individual breaker panel?
Touch one of the probes to the ground bar in the panel (where the other bare or green wires connect) and touch the other probe to the main lug. Make sure the meter is set to the AC voltage scale.

If you want to double-check, you can also get a cheap "non-contact" voltage tester which beeps and blinks when you get it close to an energized wire. This type of tester is not always 100% accurate, so it makes a good back-up tester.
 
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Old 06-27-11, 05:58 PM
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Word of caution that I was told by several electricians. If you turn off the main breaker turn off ALL the breakers before energizing again. Then proceed to turn the main one on and then all the others in turn one by one. I was told to not do so would result in a real fireworks display! Anyone else near anything different on that?
 
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Old 06-28-11, 09:07 AM
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If the breakers are all in good working order it will be no problem to switch the main with or without the branch circuit breakers. You could have trouble like you've been told if you're working on a very old panel or a panel where you suspect there may be damage to the main breaker. You may see a brief spark coming from the breaker during normal switching operation.
 
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