DMB5mil
Active member
Hi All,
I'm having trouble understanding the following scenario involving a shunt trip circuit breaker and a fire pump controller I'm mapping out. I've attached a schematic diagram. Here's the story:
A fire pump controller is connected to an automatic transfer switch which is fed from either utility power or by a standby generator as shown in the attachment.
When turned on, the fire pump controller opens the 200/3 breaker in Panel Gen in order to lighten the generator load (Panel N no longer is powered) Both the fire pump controller and generator are at 277/480V.
However, the shunt trip does not happen directly between pump controller and generator. The 20/1, 120V circuit breaker in Panel E is the mix and is somehow providing control. Here is what happens:
If the 20/1 breaker is open, when the fire pump controller is on it does NOT open the 200/3 breaker.
If the 20/1 breaker is closed, when the fire pump controller is on it DOES open the 200/3 breaker.
I can see how the fire pump controller could trip the 200/3 breaker directly (the controller acting as a switch energizes the shunt trip coil of the 200/3 breaker, causing it to open) but how does the 20/1 120V breaker fit in? Why do you suppose it is required? I can't visualize what's going on here.
Is it required because the control voltage within the pump controller is 120V, not 480V?
Any advice is appreciated. If you want to mark up the attached schematic feel free!
Thanks,
Brian
Any guidance, websites, schematics, etc. would be helpful. Maybe I need a good resource for understanding shunt trip circuit breakers...
Shunt_Trip_Question.pdf
I'm having trouble understanding the following scenario involving a shunt trip circuit breaker and a fire pump controller I'm mapping out. I've attached a schematic diagram. Here's the story:
A fire pump controller is connected to an automatic transfer switch which is fed from either utility power or by a standby generator as shown in the attachment.
When turned on, the fire pump controller opens the 200/3 breaker in Panel Gen in order to lighten the generator load (Panel N no longer is powered) Both the fire pump controller and generator are at 277/480V.
However, the shunt trip does not happen directly between pump controller and generator. The 20/1, 120V circuit breaker in Panel E is the mix and is somehow providing control. Here is what happens:
If the 20/1 breaker is open, when the fire pump controller is on it does NOT open the 200/3 breaker.
If the 20/1 breaker is closed, when the fire pump controller is on it DOES open the 200/3 breaker.
I can see how the fire pump controller could trip the 200/3 breaker directly (the controller acting as a switch energizes the shunt trip coil of the 200/3 breaker, causing it to open) but how does the 20/1 120V breaker fit in? Why do you suppose it is required? I can't visualize what's going on here.
Is it required because the control voltage within the pump controller is 120V, not 480V?
Any advice is appreciated. If you want to mark up the attached schematic feel free!
Thanks,
Brian
Any guidance, websites, schematics, etc. would be helpful. Maybe I need a good resource for understanding shunt trip circuit breakers...
Shunt_Trip_Question.pdf