circuit breaker question


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Old 11-21-08, 04:33 PM
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circuit breaker question

I have a small pushbutton type thermal circuit breaker that is rated for 10 amps, 32vDC, 250VAC. My question is does the trip amps change with the amount of voltage being used or should it trip at 10 amps no matter what the voltage.(within the voltage range)
Thanks
 
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Old 11-21-08, 04:54 PM
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The voltage won't affect the current needed to trip the breaker. It probably won't trip at 10A--it should be able to hold its rated current without tripping. The breaker will hold with current in excess of its rated current for a certain length of time--the greater the overcurrent, the faster it will trip.
 
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Old 11-21-08, 08:46 PM
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The 10 amps is for one voltage rating or the other, not both. I would guess that it is for the 250 V ac rating. Why do you ask?
 
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Old 11-21-08, 09:10 PM
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Breakers don't have a connection to ground, so they have no idea what the voltage is. They only sense current.
 
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Old 11-22-08, 06:17 AM
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The current rating is independant of voltage. The max voltage spec shows the ability to clear the fault without breaker damage at that voltage. It is tougher to clear a DC fault with that breaker, thus it is a lower spec than the AC voltage.
 
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Old 11-22-08, 06:19 AM
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Originally Posted by dzdave00 View Post
The 10 amps is for one voltage rating or the other, not both. I would guess that it is for the 250 V ac rating. Why do you ask?
It is rated for both. The reason for the large difference between AC and DC voltages -- or for any voltage rating at all -- is due to the breaker's ability to handle arc suppression.

When the breaker trips, its contacts are physically separated. A small arc is generated until the distance between the contacts is large enough to stop sustaining the arc. At a given current, an arc will span a greater distance with high voltage than it will with low voltage. That's why the breaker has a voltage rating.

As for the difference between AC and DC ratings: An AC wave crosses the zero-voltage point as it moves from positive to negative and back again. The zero crossing helps to shorten the distance at which the arc is sustained, which in turn shortens the lifespan of the arc.

DC voltage is constant. Because DC voltage has no zero crossing, distance between contacts is the only thing that stops the arc.

That's why the same breaker is rated for 250VAC and only 32VDC.
 
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Old 11-22-08, 07:31 AM
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Let me explain what we would like to do. Many customers would like to have 2 sump pumps in one pit.One primary and a backup. Alot of these people only need one pump most of the time, but at certain times (spring) a second pump is needed to keep up with the incomming water. The problem is most of these older and some newer homes only have one circuit at the pit. If one pump jams or fails it takes out the breaker and you lose the second pump as well. I know adding a second circuit would be the way to go but that isn't always easy. What we were thinking of doing was taking a small plastic junction box and running a cord w/plug into it. From there it would go to two single outlets with the breakers in between. The pumps we use only draw 4.5 amps and about 12 amps at locked rotor. We were thinking that maybe if one pump jammed or shorted out it would trip the breaker for that outlet and leave the other working. Are we way off base here or could we use a different type of breaker? The thermal one doesn't seem to trip even with 12 amps going through it.
 
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Old 11-22-08, 09:22 AM
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Thermal breakers are pretty low end. I'd go with a couple of temp. compensated magnetic breakers, perhaps closer to 6 or 7 amps rating each. The will trip quicker at 100% overload than the thermals.
 
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Old 11-22-08, 11:35 AM
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Do you think there would be a problem with this type of breaker when the pump first starts as the amps are usually alot higher on start-up vs run
 
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Old 11-22-08, 01:07 PM
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There are good magnetic/hydraulic breakers that can be had with delay trip and temp compensated. They may be a bit hard to find in non-standard values, and pricing will approach $20 ea., however. You might consider small time delay fuses, in the 1/4 x 1 1/4" glass package. Less than a dollar each, 250v rating, in 6.25, 7 amp, etc. You will need also a panel fuse holder.
 
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Old 11-24-08, 05:15 AM
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Originally Posted by Rick Johnston View Post
It is rated for both. The reason for the large difference between AC and DC voltages -- or for any voltage rating at all -- is due to the breaker's ability to handle arc suppression.

When the breaker trips, its contacts are physically separated. A small arc is generated until the distance between the contacts is large enough to stop sustaining the arc. At a given current, an arc will span a greater distance with high voltage than it will with low voltage. That's why the breaker has a voltage rating.

As for the difference between AC and DC ratings: An AC wave crosses the zero-voltage point as it moves from positive to negative and back again. The zero crossing helps to shorten the distance at which the arc is sustained, which in turn shortens the lifespan of the arc.

DC voltage is constant. Because DC voltage has no zero crossing, distance between contacts is the only thing that stops the arc.

That's why the same breaker is rated for 250VAC and only 32VDC.
Thanks, I learned something new today.
 
 

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