powerpete69
Senior Member
- Location
- Northeast, Ohio
- Occupation
- Professional Electrical Engineer
In our factory, we had a Roof top unit with a ground fault, the hot wire was laying on the chassis and immediately tripped the 70 amp breaker feeding it. There was a 600 amp breaker above it that did NOT trip. However, the 3000 amp main breaker above that 600A did trip. There is an attached picture of it.
The maximum short circuit for three phase at the RTU bus is 7,000 amps, and its maximum short circuit for line to ground is 5,500 amps per "EasyPower"
The instantaneous breaker curve of this breaker says it wont trip to 25,000 amps, so I believe that is out of play.
We believe the ground fault of the 3000 amp breaker is what tripped. It is currently set at 720 amps if you look at the picture.
Even if I set it up to its max at 1200 amps, isn't it still going to trip when a small unit like a rooftop short circuits at 5,500 amps?
Doesn't make sense to me. What am I missing and what is the main purpose of this ground fault if the setting is so low?
Knocking out a whole factory is not good when a small unit short circuits line to ground.
The maximum short circuit for three phase at the RTU bus is 7,000 amps, and its maximum short circuit for line to ground is 5,500 amps per "EasyPower"
The instantaneous breaker curve of this breaker says it wont trip to 25,000 amps, so I believe that is out of play.
We believe the ground fault of the 3000 amp breaker is what tripped. It is currently set at 720 amps if you look at the picture.
Even if I set it up to its max at 1200 amps, isn't it still going to trip when a small unit like a rooftop short circuits at 5,500 amps?
Doesn't make sense to me. What am I missing and what is the main purpose of this ground fault if the setting is so low?
Knocking out a whole factory is not good when a small unit short circuits line to ground.