# Main Circuit Breaker Test



## Joba Fett (Aug 14, 2007)

What made you take this reading in the first place...
Did you take the readings at the same location.

Oh, and your welcome.....


----------



## lthomps222 (Mar 16, 2008)

I took the readings because I lost power in certain locations of my house last night. Yes, I took the reading in the same location.


----------



## bwinters12 (Jan 23, 2008)

IF you are taking the readings on the main service WIRE then the breaker being on or off should not effect your readings. If you took the first readings from the wire and the second reading you took was off the bus bars then it sounds like the main is bad.


----------



## J. V. (Jun 1, 2007)

With the breaker turned off you should read around 120 volts from the conductor lug to ground on each leg on the line side. You should read around 240 across both lugs. With the breaker turned to the on position you should read the same as what you read on the line side. 
Bad breakers sometimes cannot be determined by checking the voltage. A current check should be performed and both values should be very close.


----------



## Speedy Petey (Feb 1, 2004)

You say you took these reading on the INPUT side of the main? 
Then turned it back on and took the same readings?

HOW can this be a bad main then???? You are getting bad readings on the LINE side, NOT the load side. 
Without a load you can get a false positive reading. As soon as a load is placed on the line the fault is exposed.

You have a problem outside the house. Call the POCO or an electrician and have them check the connections at your house, on the pole and in the meter pan. 

THIS IS NOT a main breaker problem.


----------



## bwinters12 (Jan 23, 2008)

Speedy Petey said:


> You say you took these reading on the INPUT side of the main?
> Then turned it back on and took the same readings?
> 
> HOW can this be a bad main then???? You are getting bad readings on the LINE side, NOT the load side.
> ...



I have never experienced this before. Just curious as to what would cause the false positive by adding a load


----------



## J. V. (Jun 1, 2007)

bwinters12 said:


> I have never experienced this before. Just curious as to what would cause the false positive by adding a load


CURRENT FLOW!!!!!!!!!


----------



## bwinters12 (Jan 23, 2008)

Thats a very detailed answer. How would current flow explain a reading of 120 volts on a feed that has no voltage.


----------



## 220/221 (Oct 9, 2007)

You have to read voltage BETWEEN the legs.

The 120 on the dead leg is being beckfed from the live leg via a 240V circuit or multi wire branch circuit.



ALWAYS test phase to phase.


----------



## bwinters12 (Jan 23, 2008)

220/221 said:


> You have to read voltage BETWEEN the legs.
> 
> The 120 on the dead leg is being beckfed from the live leg via a 240V circuit or multi wire branch circuit.
> 
> ...


He stated he shut the main off and read 120 on both legs so it could not be back fed through the 240 v circuits cause they are not getting any power


----------



## Speedy Petey (Feb 1, 2004)

There is no current flow on the legs when the main is off. With the main on the current flows on the one good leg and the open leg is exposed since current is trying flow on it but cant.


----------



## 220/221 (Oct 9, 2007)

> He stated he shut the main off and read 120 on both legs so it could not be back fed through the 240 v circuits cause they are not getting any power


 
Since he is a newbie I assumed that he didn't necessarily describe things correctly. They tend to mix up the whole in/out thing.

Anyways....ALWAYS test phase to phase.


----------



## lthomps222 (Mar 16, 2008)

*Here is a picture and more detailed info.*

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.


----------



## micromind (Mar 9, 2008)

There's no question about it, you have an open somewhere from the main breaker back into the power lines. It could be anywhere. Time to get the POCO involved, it's likely their problem. (They actually like fixing stuff on Sunday, it's overtime.)

The reason you get 120V with the breaker off is because of 'capacitive coupling' of the wire. If you're using a digital multimeter, its input impedance is very high, meaning it doesn't 'load' the circuit much. Wires next to each other that are open on both ends (like the left one is now) tend to pick up voltage from the other ones. Even if they're insulated. Usually the current is very low, so no hazard exists, but voltage induced this way in an overhead power line several miles long can easily kill a lineman. (And has!) 

In your case, there's enough capacitive coupling the make the meter read, but when you turn the breaker on, the load of the building cancels this out. The result is a very low voltage reading. 

Trace the wire back, and make sure anything you have acess to is tight. Don't cut the seal or pull the meter, the POCO will do that for you. If it's good all the way to the meter, then it's the POCO's problem. 

Rob


----------



## 220/221 (Oct 9, 2007)

ALWAYS test phase to phase.




awwww....never mind.


----------



## jkdsbabydoll (Nov 7, 2010)

*electrical problems help*

our main breaker in the house when tested is reading only 120/110 volts on the tester but our dryer and electric range is working fine (220 volts. ) Those breakers operate the backside of the lights and outlets in the house.All of that is fine. It's the front side lights and outlet in the house that have stopped working.When we test those breakers they bareley test any trace of voltage unless we ground it to the netural panel on the back and then it test normal.Does anyone know what may be wrong.:wink: help please.Thank you ,jkdsbabydoll.


----------

