Main tripping

[glennyamada]

What could cause the main breaker to trip before the ocp breaker? Is it the sensitivity of the main breaker(short circuit rating)? In this situation the main trips when the stove top is turned on. 50/50 does not trip. Wiring is good.

:-?

 

[ActionDave]

I assume by ocp you mean the breaker that feeds the stove.

What else is on or being used when the stove trips the main? Or conversely what is not being used when the main doesn't trip?

 

[jim dungar]

Except for very high fault currents (at least >40kA) the AIC rating of breakers has no impact on the speed at which they operate.

By 50/50 do you mean a 2-pole 50A breaker? What size is your main? What brand?

 

[glennyamada]

Main tripping

The main trips when the stove top is turn on. No other device is on this circuit. The main won't trip if the stove top is not on.

 

[glennyamada]

Main tripping

The main is 100amps. Yes it is a double pole 50. I don't recall the brand name?

 

[ActionDave]

Perhaps the main is tripping because it is close to being fully loaded when the stove is turned on.

What else in the house is on when the stove is turned on and trips the main?

 

[SG-1]

Try turning off all breakers in the panel except the Main & the 50A for the stove. Then crank up the stove & see if the Main still trips.

 

[TerryBarnhill]

Does it trip instantly or over time? If one of the main lugs has loosened up, will cause it to overheat and trip.

 

[Rick Christopherson]

If the main is tripping, you don't have an overload condition, but a short circuit condition. The circuit breakers are not operating in their thermal range, but in their instantaneous magnetic trip range. It is just a matter of which breaker has the faster electromechanical reaction time. Even though this could vary by just a few milliseconds, once the faster device trips, the condition for the trip is removed, so the second device does not trip. Because the main breaker is seeing additional loads, its trip mechanism will be pre-loaded, so to speak, so it may have a shorter reflex time than it would if both breakers were going from zero load to full trip.

 

[glennyamada]

Main tripping

If the main is tripping, you don't have an overload condition, but a short circuit condition. The circuit breakers are not operating in their thermal range, but in their instantaneous magnetic trip range. It is just a matter of which breaker has the faster electromechanical reaction time. Even though this could vary by just a few milliseconds, once the faster device trips, the condition for the trip is removed, so the second device does not trip. Because the main breaker is seeing additional loads, its trip mechanism will be pre-loaded, so to speak, so it may have a shorter reflex time than it would if both breakers were going from zero load to full trip.

So my solution is to change the main breaker and find the short circuit? If the short is not in the wiring then it must be in the appliance?

 

[jim dungar]

Because the main breaker is seeing additional loads, its trip mechanism will be pre-loaded, so to speak, so it may have a shorter reflex time than it would if both breakers were going from zero load to full trip.

Preloading does not affect the 'short circuit' trip time of a fuse or breaker. When performing a coordination study, there are no standards for including 'loading' when evaluating short time and instantaneous trip times.