Partial Jag failure?

[diviney]

Originally Posted by Mike Betts

JW,

If you look at the spec sheet for the MX5-A40, you can pull 133A through the circuit breaker for about 3 seconds before it trips. This can be a long time for a resistor to gain heat depending on the thermal resistance of the resistor.

Mike:

I was looking for breaker information when I found your post... You state that the MX5-A40 can deliver 133A for around 3 seconds. As I read the data sheet, 133A represents around a 300% overload, which would trip in substantially less than 3 seconds (0.5 to 1.1 seconds). Am I missing something?

-Tom

[Al Skierkiewicz]

Tom,
You reading is correct. The smaller breakers have a slightly different trip spec and the 120 amp breaker is longer still. However, all of the resettable breakers will have a shorter trip spec after the first reset as the breaker is already at an elevated temperature. This is also compromised if the breaker is in a hot environment. i.e. near a hard working motor(s) or thermal shadow, adjacent breakers are also passing a lot of current or if the wiring attached to the PD has not been properly terminated (high resistance) and is creating heat from the termination.