Home>Discussions>ELECTRICAL & LIGHTING>Main Circuit Breaker Voltage Reading
29 posts / 0 new
Last post
lthomps222
Main Circuit Breaker Voltage Reading

I tested the voltage of the two main hot wires going into my main circuit breaker (the circuit breaker was off). The voltage read 124V on each. I then turned the circuit breaker on and re-tested the voltage. One wire tested at 0V and the other tested at 122V. Does this mean I have a bad main circuit breaker?

djohns
Re: Main Circuit Breaker Voltage Reading

Did you read 0 volts on the load side of the breaker ?
If you did , " excercise " the breaker a couple of times and recheck . Make sure all connections are tight ( use extreme caution ) .

lthomps222
Re: Main Circuit Breaker Voltage Reading

I don't know what you mean by load side of breaker. I will go take a picture.

lthomps222
Re: Main Circuit Breaker Voltage Reading

Here is the picture. Do you see where it says "MAIN" it has two wires. I tested each wire. When I went back to take the picture I tested it again. The wire on the left read 60V and the wire on the right read 122V.

Attachment: 
djohns
Re: Main Circuit Breaker Voltage Reading

That looks like the wires coming from the meter base . Possibly a bad connection in there or anywhere back to the transformer secondary . If everything is clean and tight in the breaker box , then it's time to backtrack . That will involve an electrician and possibly your power company. I would start with the power company . They won't charge you for checking out their connections .

What started this investigation ?

lthomps222
Re: Main Circuit Breaker Voltage Reading

Thanks! Another question, should it be reading 120V on both sides? Is it possible the breaker is bad? Is it possible one side of a breaker can go bad?

lthomps222
Re: Main Circuit Breaker Voltage Reading

What prompted the investigation? Last night I lost power to certain parts of my house and outlets. Occasionally the power would come back on and then go off again. None of the breakers were tripped.

djohns
Re: Main Circuit Breaker Voltage Reading

Yes , one side of a 2 pole breaker can fail . Are you losing the voltage on the LOAD side of the breaker or on the incoming wires ? Big difference .

lthomps222
Re: Main Circuit Breaker Voltage Reading

I believe its what you call the load side. Here's a better description.

Ok guys, here is a picture of what I am working with. I think I know what's wrong. I am only touching the breaker that says "main" in the photo. Do you see those two screws on the breaker that says "main"? That's where I am taking my voltage measurements using a multimeter.

Scenario 1: "main" breaker is set to "off" position. I put one multimeter lead on a ground and the other on the left side screw of the "main" breaker. Multimeter reads 120V. Next I put one multimeter lead on a ground and the other on the right side screw of the "main" breaker. Multimeter reads 120V.

Scenario 2: "main" breaker is set to "on" position. I put one multimeter lead on a ground and the other on the left side screw of the "main" breaker. Multimeter reads 4V. Next I put one multimeter lead on a ground and the other on the right side screw of the "main" breaker. Multimeter reads 120V.

Attachment: 
djohns
Re: Main Circuit Breaker Voltage Reading

Check your PM box .

lthomps222
Re: Main Circuit Breaker Voltage Reading

What does PM stand for? I'm a newbie.

Pages

TV Listings

Find TV listings for This Old House and Ask This Old House in your area.