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Old 04-08-2009, 02:01 AM   #1
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Can I test to verify amp rating on a circuit breaker with a multimeter?


My circuit breakers have red stickers on the switches showing the amp rating (20 amp and 15 amp). I would like to verify that this is correct. Can I use a multimeter to test this? If so, do I test this at the panel at the wires coming out of the breaker or at a receptacle that is connected to that circuit?

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Old 04-08-2009, 06:22 AM   #2
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Can I test to verify amp rating on a circuit breaker with a multimeter?


Amps are checked with an amprobe not a multi-master. And even this will not be able to test the trip capacity of a breaker. Why would you assume the labels can be wrong? These are normally molded into the breaker.

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Old 04-08-2009, 09:58 AM   #3
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Can I test to verify amp rating on a circuit breaker with a multimeter?


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Originally Posted by Bob Mariani View Post
Amps are checked with an amprobe not a multi-master. And even this will not be able to test the trip capacity of a breaker. Why would you assume the labels can be wrong? These are normally molded into the breaker.
The labels on the actual switch is a red sticker. I was just curious if I can verify they are indeed the correct value.
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Old 04-08-2009, 10:18 AM   #4
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Can I test to verify amp rating on a circuit breaker with a multimeter?


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Originally Posted by Bob Mariani View Post
Amps are checked with an amprobe not a multi-master.
Multimeters are called multimeters because they have multiple functions, your better meters have an ammeter built into them, but they are usually capable of 10 amps or less.

Your breaker should say on it somewhere what it's trip rating is.
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Old 04-08-2009, 10:53 AM   #5
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Can I test to verify amp rating on a circuit breaker with a multimeter?


Still any meter is checking the load amps. Not the trip setting of a breaker. These labels are correct, no reason to assume otherwise.
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Old 04-08-2009, 01:58 PM   #6
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Can I test to verify amp rating on a circuit breaker with a multimeter?


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Originally Posted by diymonkey View Post
My circuit breakers have red stickers on the switches showing the amp rating (20 amp and 15 amp). I would like to verify that this is correct. Can I use a multimeter to test this? If so, do I test this at the panel at the wires coming out of the breaker or at a receptacle that is connected to that circuit?
Find the trip curve for your breaker, plug in 3 ea. 10A hair dryers and time how long it takes to trip. This is for the I squared T portion of the curve.

E.g. for the trip curve below
http://ecatalog.squared.com/pubs/Cir...ers/736-09.pdf
30A would be 2x rated current for a 15A breaker and 3/2 rated current for a 20A breaker. For the 3/2 it looks like a trip time of 40 sec to 250 sec passes.

You can also check for the max trip current but that is only for someone who is very familiar with electric current and you'd need to wear face protection.
http://www.google.com/search?hl=en&s...22&btnG=Search

For this trip curve, it would be 30x rated current, either 450A or 600A but it should be AC, for 16 milliseconds.
In principle, you could then use this equation
http://home.earthlink.net/~jimlux/hv/fuses.htm
with the proper wire size for your current and time elapsed.

I don't recommend you do this max current test.

Last edited by Yoyizit; 04-08-2009 at 02:26 PM.
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Old 04-08-2009, 07:27 PM   #7
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Can I test to verify amp rating on a circuit breaker with a multimeter?


Brand of breaker? Picture?
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Old 04-09-2009, 09:47 AM   #8
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Can I test to verify amp rating on a circuit breaker with a multimeter?


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Originally Posted by diymonkey View Post
The labels on the actual switch is a red sticker. I was just curious if I can verify they are indeed the correct value.
Do you have any reason to doubt the stickers?

As mentioned, breakers do not trip at exactly the rated current. They have trip curves which are based on current vs. time relationships, and they must trip within a certain time when the current exceeds the rated current. The higher the overload, the quicker the trip.

An aged or frequently tripped breaker might even trip before it would be expected to, even at a current lower than the rated current (lower than 15A for a 15A rated breaker).

If you have a reason to doubt that a breaker is what it says it is, or if you think it is tripping before (or longer) than it should, then replace it. (Measuring the current while it trips would tell you this if you had an ammeter)
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Old 04-09-2009, 10:33 AM   #9
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Can I test to verify amp rating on a circuit breaker with a multimeter?


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Originally Posted by rgsgww View Post
Brand of breaker? Picture?
Its an FP panel. Before anyone says anything, I know they are "garbage" and a fire hazard. I read all the stuff online about them and I plan on replacing it sometime next year.

Click for picture
http://img.photobucket.com/albums/v1...e/IMG_5756.jpg
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Old 04-09-2009, 11:40 AM   #10
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Can I test to verify amp rating on a circuit breaker with a multimeter?


Hmmm...double post that was not my fault, glitch.

Last edited by rgsgww; 04-09-2009 at 02:16 PM.
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Old 04-09-2009, 11:42 AM   #11
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Can I test to verify amp rating on a circuit breaker with a multimeter?


With those breakers, I'm sure the safety difference between a 15 and 20 isn't great

I'm not sure what to say, looks like original stickers. I would just stick to the size of the original conductors if I had to, but I probably wouldn't touch that system without a new panel.

Those grounds are not installed properly, are they even bonded to the neutral?

You don't necessarily need to redo the whole service, unless there is something wrong with it.
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Old 04-09-2009, 01:58 PM   #12
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Can I test to verify amp rating on a circuit breaker with a multimeter?


Haha, looks exactly like the panel I have installed in my house right now! I too have intentions on replacing the panel very soon. I really like the Square D panels and will install a 40 or 42 space QO 200 amp panel. The transformer is right in my front yard so the additional power shouldn't be of concern.

I would trust that the labels are correct, I have had no reason to believe the breakers are incorrectly labeled in my panel. Though I am not doing anything to intentionally test the capacity of the breakers.
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Old 04-09-2009, 02:17 PM   #13
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Can I test to verify amp rating on a circuit breaker with a multimeter?


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Originally Posted by theatretch85 View Post
Haha, looks exactly like the panel I have installed in my house right now! I too have intentions on replacing the panel very soon. I really like the Square D panels and will install a 40 or 42 space QO 200 amp panel. The transformer is right in my front yard so the additional power shouldn't be of concern.

I would trust that the labels are correct, I have had no reason to believe the breakers are incorrectly labeled in my panel. Though I am not doing anything to intentionally test the capacity of the breakers.

Qos are very nice. I don't like the push in style of most breakers though... I accidentally popped about 4 qos out under load.
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Old 04-09-2009, 02:38 PM   #14
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Can I test to verify amp rating on a circuit breaker with a multimeter?


They look like original FP stickers I would not mess with them.

The right size conductors should be used according to the stickers.

Q. Why do you want to test them??

Q. Are you changing something or having a problem??
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Old 04-09-2009, 04:16 PM   #15
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Can I test to verify amp rating on a circuit breaker with a multimeter?


Quote:
Originally Posted by SULTINI View Post
Q. Why do you want to test them??
I was just curious if I could verify the amperage. One of the stickers is crooked and with some of the other half-a** stuff I've seen done to the house, I was skeptical that the stickers were from the manufacturer or if the installer/homeowner put the stickers on.

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Originally Posted by SULTINI View Post
Q. Are you changing something or having a problem??
I am adding a receptacle and ceiling vent in my bathrooms. The bathroom currently only has a wall light, 1 in each bathroom, and both are on a 20amp circuit.

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