How to size DC breaker for switchgear "close" control circuit.

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nuckythompson

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I have a 4160V breaker, with 129Vdc control voltage. The "close" control circuit has a 20A breaker.

In this circuit, there is a spring charging motor (10A), and a close coil (5A). These currents are from the manual.

How was this breaker sized? Is it possible to use a 15A?
 
nuckytaylor said:
I have a 4160V breaker, with 129Vdc control voltage. The "close" control circuit has a 20A breaker.

In this circuit, there is a spring charging motor (10A), and a close coil (5A). These currents are from the manual.

How was this breaker sized? Is it possible to use a 15A?
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You could probably get by with 15 amp breaker. But why take chances. A 20 amp breaker is probably a better option and it's not like it's going to make any real difference as far as protection goes for the circuit.
 
Thanks for your response, but I am more so trying to understand how these breakers are sized.

The existing 20A failed and all I had in the shop was a 15A replacement, but I got the 20A to work.
 
How would you size it?

Charging (10A), close (5A), trip (5A).

It's not continuous load.
If i assume total load of 20A x 125% = 25A.. I would use a 25A breaker.
If I assume max loading of 10A x 125% = 12.5A.. I would use a 15A breaker.
 
nuckytaylor said:
How would you size it?

Charging (10A), close (5A), trip (5A).

It's not continuous load.
If i assume total load of 20A x 125% = 25A.. I would use a 25A breaker.
If I assume max loading of 10A x 125% = 12.5A.. I would use a 15A breaker.
Click to expand...
If they are all simultaneous, 25 A makes the most sense to me. It seems to me though that the worst case is 15 A so maybe 20 A is the answer. Given how brief of a time any of these loads are on, it seems likely that just about any value would work since the load won't be on long enough to trip.
 
The close solenoid can have a pretty high inrush current as can the spring charging motor. My only concern with the 15 A breaker would be nuisance tripping on closing. I would have no concerns about overload, since these loads are intermittent. Probably a 15 A would work, but 20 A would be a safer choice. So there is only one 4160 V breaker on this circuit?
 
David Castor said:
The close solenoid can have a pretty high inrush current as can the spring charging motor. My only concern with the 15 A breaker would be nuisance tripping on closing. I would have no concerns about overload, since these loads are intermittent. Probably a 15 A would work, but 20 A would be a safer choice. So there is only one 4160 V breaker on this circuit?
Click to expand...
likely the IT trip point is about the same for a 15 or a 20 A CB.
 
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