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Old 08-24-2010, 05:31 PM   #1
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Default inverse time breaker

I was recently looking over some specs. for a diesel exhaust removal system. the specs say the breaker must be a 60 amp inverse time breaker since it is a motor circuit, so i call supply house and ask for price on breaker and the guy says he's never heard of an inverse time breaker, in fact none of the counter people had, so i guess my question is when you buy a 60 amp 2-pole breaker is it an inverse time (are all breakers inverse time?) or is it something i'll have to go to the manufacturer for??
any info would help, thx

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Old 08-24-2010, 05:49 PM   #2
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I believe all breakers are now inverse time.. you dont buy a special breaker for your ac or other motor loads.. the normal breakers you buy should be qualified.. but im not a 100% on this

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Old 08-24-2010, 05:54 PM   #3
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Most off-the-shelf breakers have two modes used to trip it.

One is a magnetic system, which detects a gawd-awful amount of current (usually caused by a short circuit).

The other is a thermal system, which, depending on the amount of current, will take difference amounts of time to trip.

A 20a breaker will not trip at 20.000000000001 amps. It may not ever trip at 22 or 23 amps. It may trip in 5 minutes at 25 amps, 1 minute at 30 amps, 15 seconds at 40 amps, etc. This is what is meant by 'inverse time'.
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Old 08-24-2010, 05:55 PM   #4
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Almost all molded case breakers are inverse time.
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Old 08-24-2010, 06:00 PM   #5
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I believe the only molded case breakers that aren't inverse time are ones that only have a magnetic-trip.

All "inverse time" means is that as the current goes up, the time to trip decreases. I may be talking out of my back-side, but I think any breaker with a "trip curve" qualifies as an "inverse time" breaker. That trip curve is nothing but a graph of how time decreases as the current increases.

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Old 08-24-2010, 06:16 PM   #6
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sounds good, you learn something everyday, thanks for the help
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Old 08-24-2010, 06:24 PM   #7
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what supply house was that ?
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Old 08-24-2010, 07:10 PM   #8
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Quote:
Originally Posted by ohiosparky99 View Post
sounds good, you learn something everyday, thanks for the help
Everything that was said above is correct, I am shocked a supply house guy would not know that.
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Old 08-24-2010, 07:31 PM   #9
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State electric
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Old 08-24-2010, 08:33 PM   #10
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Quote:
Originally Posted by Zog View Post
Everything that was said above is correct, I am shocked a supply house guy would not know that.
I ain't. A lot of suppliers are on the ball, but I've run into some serious yokels; the guy who thought a quad receptacle cover was called a "duplex," because "duplex" means "two" and a quad holds two "normal" receptacles.

-John

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