Testing a circuit breaker

[bluedog225]

Holy smokes, I didn‘t think I could hate the interwebs more….

I’ve bounced around a half dozen sites telling me how to see if a circuit breaker has current passing through it.

Is there a safe way to test if it will trip when overloaded?

I picked up a seemingly new Siemens 100 amp breaker for my cabin at restore. I’m hesitant to throw it into service.

Thanks

 

[Crabman]

You may want to move this here;

Lighting & Electrical

Don't SHOCK yourself...

www.garagejournal.com

Good luck, not sure how to generate that big a load.

 

[The Cobbler]

thread moved to electrical forum

 

[manwithtools]

I've got a pair of dykes that have tested at least three 20 amp circuit breakers in the last 40 years
I'm not going to suggest that method for a hundy though...

 

[bluedog225]

Sorry. I tend to post everything in general and forget there are sub forums.

 

[rlitman]

Does it appear physically damaged? Any signs of corrosion or overheated contacts? Can you switch it on and off, and does it click as expected. If that much checks out, I'd say you're good to go. There's not much that can go wrong in a sealed miniature circuit breaker. This is a QP type, right?

 

[manwithtools]

Does it appear physically damaged? Any signs of corrosion? Can you switch it on and off, and does it click as expected. If that much checks out, I'd say you're good to go. There's not much that can go wrong in a sealed miniature circuit breaker. This is a QP type, right?

Agree with this. There's not too much to go wrong and if it's genuine Siemens and fairly clean I'd say it's likely fine.

 

[LopezBart]

Holy smokes, I didn‘t think I could hate the interwebs more….

I’ve bounced around a half dozen sites telling me how to see if a circuit breaker has current passing through it.

Is there a safe way to test if it will trip when overloaded?

I picked up a seemingly new Siemens 100 amp breaker for my cabin at restore. I’m hesitant to throw it into service.

While I can certainly think of ways to do this, none of them are really safe since they end up using your cabin as a test bed.
Circuit breakers (esp. larger ones) are an important safety mechanism; for less than $100 new and without knowing that the used one was removed in good working order, I'd likely spring for a new one.

 

[rlitman]

We're not talking about Federal Pacific, so with a simple thermal-magnetic breaker that functions, they're pretty bullet proof. And they need to be when you expect them to have a 50+ year service life, installed in millions of locations.

To expound on what I posted above, being able to turn it off means the contacts aren't welded together and the spring is good, which means the breaker is able to open on it's own. The biggest concern I'd have is with the clips that hold onto the bus. Corrosion there can lead to a burnt bus bar.

Now if you have some electrical engineer friends over your shoulder to help, you CAN test the breaker safely. The "secret" is to test it at a very low voltage. Circuit breakers interrupt the circuit above a threshold current (which for an instantaneous break will be surprisingly high). But under a volt, the probably close to a thousand amps needed to trip that breaker magnetically (no, it won't simply trip as you pass 100A - breakers don't work that way) isn't nearly as dangerous as it would be at 240V. But please don't take that as a recommendation from me to try something that silly.

 

[micromind]

To test a breaker that size, you'd need a breaker test set.

This is a device that can put hundreds of amps(the larger models can go several thousand amps) through a breaker at a low voltage, usually less than 5 volts.

Breakers trip on amps, voltage doesn't matter except low voltage doesn't stress the contacts anywhere near as much as operating voltage does.

For a small breaker like that, I'd give it good examination, especially smell the front end of it where it connects to the bus. If you smell anything that even remotely resembles burned plastic or an electrical arc, get rid of it.

Next I'd operate it a few times, uninstalled. Then with it closed (on), sort of slam it onto a table top, load end down. Not too hard of course but it should trip. If it doesn't, there's something wrong with the internal mechanism and it isn't safe to use.

If it does ok, I would have no problem installing it into a panel.

 

[sparky 1971]

I would use if it appears ok and not lose a bit of sleep. If it's keeping you up all night worrying about it, buy a new breaker. They are only about $75.00.

 

[bluedog225]

It looks new. Snaps well. No tool marks. No burned odor. No burned contacts.

Undisturbed “factory” grease in the fitting where it connects. Type QP.

Pics below.

One thing I’m not familiar with (probably because I haven’t looked), is the white material above the terminal screws in the photo. Is that kosher?

Thanks

 

[sparky 1971]

It looks new. Snaps well. No tool marks. No burned odor. No burned contacts.

Undisturbed “factory” grease in the fitting where it connects. Type QP.

Pics below.

One thing I’m not familiar with (probably because I haven’t looked), is the white material above the terminal screws in the photo. Is that kosher?

Thanks

Run it.

 

[bluedog225]

Will do.

It passed the slam test as well.

Hard to pass it up at $5.

Thanks all!

 

[Zeke]

I've got a pair of dykes that have tested at least three 20 amp circuit breakers in the last 40 years
I'm not going to suggest that method for a hundy though...

Yeah, I've got a needle nose with a nice bite out of one side. I always 'flash' back to that day and moment.

 

[wyliesdiesels]

We're not talking about Federal Pacific, so with a simple thermal-magnetic breaker that functions, they're pretty bullet proof. And they need to be when you expect them to have a 50+ year service life, installed in millions of locations.

To expound on what I posted above, being able to turn it off means the contacts aren't welded together and the spring is good, which means the breaker is able to open on it's own. The biggest concern I'd have is with the clips that hold onto the bus. Corrosion there can lead to a burnt bus bar.

Now if you have some electrical engineer friends over your shoulder to help, you CAN test the breaker safely. The "secret" is to test it at a very low voltage. Circuit breakers interrupt the circuit above a threshold current (which for an instantaneous break will be surprisingly high). But under a volt, the probably close to a thousand amps needed to trip that breaker magnetically (no, it won't simply trip as you pass 100A - breakers don't work that way) isn't nearly as dangerous as it would be at 240V. But please don't take that as a recommendation from me to try something that silly.

a breaker can open regardless of what the handle is doing.

 

[Bert_]

I've got a pair of dykes that have tested at least three 20 amp circuit breakers in the last 40 years
I'm not going to suggest that method for a hundy though...

Those are rookie numbers

 

[wyliesdiesels]

It looks new. Snaps well. No tool marks. No burned odor. No burned contacts.

Undisturbed “factory” grease in the fitting where it connects. Type QP.

Pics below.

One thing I’m not familiar with (probably because I haven’t looked), is the white material above the terminal screws in the photo. Is that kosher?

Thanks

that is bakelite packing

is your breaker panel a siemens?

 

[bluedog225]

Yes. I got a new Siemens 200 amp panel at Restore as well. And thanks

 

[Norcal]

They do not test smaller circuit breakers as it is too costly, the testing would cost more then the breaker is worth.

 

[sparky 1971]

I've got a pair of dykes that have tested at least three 20 amp circuit breakers in the last 40 years
I'm not going to suggest that method for a hundy though...

I do that to a newish pair of dykes at least twice a year. Sometimes more. I bet I've gone threw at least 20 pair. The last time it was the very first cut with a set I bought less than an hour before.

 

[ArcReactorKC]

I have a primary injection tester capable of 5000a. It has never occured to me to test a breaker less than 400a.

Maybe I should flesh out our portfolio to residential breaker testing

 

[rlitman]

It looks new. Snaps well. No tool marks. No burned odor. No burned contacts.

Undisturbed “factory” grease in the fitting where it connects. Type QP.

Pics below.

One thing I’m not familiar with (probably because I haven’t looked), is the white material above the terminal screws in the photo. Is that kosher?...

Circuit breakers are made from thermoset plastic (bakelite or something along those lines). It's a material that withstands high temperatures and does not melt. The packing could me more of the same, or possibly a type of fire-cement. With a small breaker like this, you want a good seal on the case so that any arcing that happens inside is safely contained within.

To me, the undisturbed factory grease is the most important part. Looks great to me.

a breaker can open regardless of what the handle is doing.

Yes, not disagreeing with you, but you mis-read me. My point about opening it via the handle was that this proves that it can open internally. Yes, it is possible for a breaker to open with the handle stuck in the closed position. The unorthodox thwap test above is an example of this. But there are situations where the breaker may be unable to open at all, and simply opening the handle eliminates those possibilities.

 

[mm08822]

One thing I’m not familiar with (probably because I haven’t looked), is the white material above the terminal screws in the photo. Is that kosher?

The white fire-cement material is used to cover a factory adjustment screw (yellow highlight below). Nothing for the end-user to mess with.

 

[BreeStephany]

I have a primary injection tester capable of 5000a. It has never occured to me to test a breaker less than 400a.

Maybe I should flesh out our portfolio to residential breaker testing

What make / model is your primary injection tester?

 

[toplessHO]

I do that to a newish pair of dykes at least twice a year. Sometimes more. I bet I've gone threw at least 20 pair. The last time it was the very first cut with a set I bought less than an hour before.

I tell the young pups
unless you can see that both ends arent connected to any power source,assume its "hot"

 

[alfredeneuman]

unless you can see that both ends arent connected to any power source,assume its "hot"

Additionally I'd say test the wires with a voltage tester to verify that they're not hot.

 

[David Paul]

I’ve been tempted but never tried it:

 

[johnre]

Products such as circuit breakers are over-engineered, tested when manufactured, and have a lot of QA steps and regulatory agency scrutiny applied when they are first designed.

They furthermore get regular feedback from the field while in use if there is any issue found - professionals such as insurance adjustors, fire investigators, etc. have avenues to make sure that their input is heard and gets a follow-up. How do you think Federal Pacific’s problems were found when you’re talking about parts-per-thousand?

There is no 100% assurance of anything. But some things you can trust better than others to just work.

I don’t haver to test the airbags on my vehicle, or the seat belt tensioning system. It’s just expected to work.

 

[mike93lx]

I’ve been tempted but never tried it:

 

[wyliesdiesels]

I dare you to plug that into a 5000a 480v service!

 

[23ford]

taught by old tim electrician to test a breaker by tuning it on outside the box take the breaker and strike on the other hand to see if it trips.........

 

[foolishpride]

I have a primary injection tester capable of 5000a. It has never occured to me to test a breaker less than 400a.

Maybe I should flesh out our portfolio to residential breaker testing

Why in the world would you have your own high current test set? I worked for a testing company for 31 years doing primary injection testing on low voltage circuit breakers up to 4000 amps. Hated doing those breaker jobs! Hard on your back!

 

[ArcReactorKC]

Why in the world would you have your own high current test set? I worked for a testing company for 31 years doing primary injection testing on low voltage circuit breakers up to 4000 amps. Hated doing those breaker jobs! Hard on your back!

I own a critical power company. We perform maintenance/upgrades/commissioning on automated switchgear, anything under 14.4kv (used to be 55kv but insurance...)

 

[foolishpride]

I own a critical power company. We perform maintenance/upgrades/commissioning on automated switchgear, anything under 14.4kv (used to be 55kv but insurance...)

Sounds like we had a lot in common! I spent 26 years imbedded in a steel mill, helping maintain their power system. Don't miss it one bit, LOL!