Testing a breaker. - SailNet Community
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post #1 of 29 Old 03-02-2011 Thread Starter
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Testing a breaker.

I was doing some AC wiring on my boat (upstream from the GFI's), and didn't bother to throw the breaker. I know, I know... Dumb! What can I say, I like living on the edge! The wire striper grounded and WHAM...GOODNESS GRACIOUS...GREAT BALLS OF FIRE (and a rather loud noise as well)! You should see the tool. The stripper for #10 wire is now a #6! Anyway, the breaker on the dock box didn't trip. Seems like it should have, the only time I've seen a flash this big was with 220. How can I test the breaker (other than the way I did!)?

Last edited by L124C; 03-04-2011 at 11:35 PM.
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post #2 of 29 Old 03-02-2011
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Dock
Which breaker are you wanting to test??

a) the dock box breaker
b) your AC main breaker
c) your downstream AC breakers?

The dock box breaker may or may not trip on short circuit like that depending upon just how long your shore power cable is, what the wiring is like and what condition the breaker is in - but it should be an GFI breaker with a test button... at least all the ones I've ever seen are.

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post #3 of 29 Old 03-02-2011
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The breaker that should go is the one on the circuit you were trying to weld with.
If it breaks the circuit there is no reason for the others to go. If you have individual circuits - and you should have - and it doesn't go with a dead short it might need replacing.

Brian
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..of course, any breaker that has what looks like rust leaking out of the back of it should also be replaced.

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True, but a good breaker will not rust.

Brian
Living aboard in Victoria Harbour
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post #6 of 29 Old 03-02-2011
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how to test

rig up a cord that will plug in to the dock box with at least 6 plugs. a modded power strip with the plug end and built in breaker removed would work well. then plug in a 500 watt flood light. every 500 watts is a tad over 4 amps.

then just keep plugging in stuff, like heaters, they are nice because they have different levels.

once you get just over the rating of the breaker you need to wait a few mins. as they wont blow right away with just a small over load, it takes a few.
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Quote:
Originally Posted by mitiempo View Post
True, but a good breaker will not rust.
This was a good breaker - 30 years ago:

Testing a breaker.-dsc00048.jpg

It's not the copper that's the problem - the bi-metallic strip (thermal trip), spring-steel spring and the set screws that hold the internals together in your typical off-the-shelf circuit breaker eventually rust up and fail although you can buy magnetic-only breakers for certain applications that will last a little bit longer.

I don't have any pics of the front unfortunately, but needless to say it doesn't operate any more.

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post #8 of 29 Old 03-02-2011
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Dock
Quote:
Originally Posted by scottyt View Post
how to test

rig up a cord that will plug in to the dock box with at least 6 plugs. a modded power strip with the plug end and built in breaker removed would work well. then plug in a 500 watt flood light. every 500 watts is a tad over 4 amps.

then just keep plugging in stuff, like heaters, they are nice because they have different levels.

once you get just over the rating of the breaker you need to wait a few mins. as they wont blow right away with just a small over load, it takes a few.
You're serious??

If the breaker isn't working, hopefully the "modded power strip with the plug end and built in breaker removed" won't blow it's internals out at you first..

Besides, this isn't actually testing the breaker's capacity to trip on a short circuit.

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Last edited by Classic30; 03-02-2011 at 09:55 PM.
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post #9 of 29 Old 03-02-2011
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I live aboard and with heaters as well as occasional use of microwave and maybe a kettle I and my neighbors all know the breakers on the dock works with an overload. And as long as they work with an overload they will work with a dead short as far as I know.
But if the problem is on your boat the dock breaker shouldn't blow unless it occurs before your main breaker.

Brian
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post #10 of 29 Old 03-03-2011
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yes hart i am serious, i have a power strip with internal breaker removed. just for testing breakers, it works well. I have used it up to a 40 amp breaker before. if its a two pole break just test each phase separately. also you need to remember that our power is different than yours. yes it gets warm under a larger load, but its not like your walking away for hours.

now a short trip test is a little riskier and certainly much brighter. actually i will replace a breaker before i short test it on purpose.

sometimes you need to rule out other problems that just changing the breaker wont show you. i have seen some crazy things, like 1 15 amp circuit trying to power a 20 amp load ( a big window ac unit ) that would run fine as long as it did not cycle more than every 5 mins and the tv was off.
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