Minimum Vertical Bus Rating

Status
Not open for further replies.
E

eanton22

Inactive, Email Never Verified
A specification for a Motor Control Center calls out for a minimum continuous current bus(vertical) rating of 800A. The Circuit Breaker at the swgr is 800A.

Why is this a minimum?? Shouldn't it be maximum current rating of 800A?

What happens when the minimum is not reached, say 600A instead of 800A??
 
What they are saying is that when you go out shopping for an MCC, you need to buy one that is capable of handling at least 800 amps worth of load. The vertical bus bars internal to the MCC are connected to the incoming power source, and that will have an 800 amp breaker, so it is important that the bus bars not be at risk of being damaged by that level of current.
 
eanton22 said:
A specification for a Motor Control Center calls out for a minimum continuous current bus(vertical) rating of 800A. The Circuit Breaker at the swgr is 800A.

Why is this a minimum?? Shouldn't it be maximum current rating of 800A?

What happens when the minimum is not reached, say 600A instead of 800A??
Click to expand...

Presuming that we're talking about 480V system. An 800A feeder breaker form the switchgear would require an MCC with a horizontal bus if 800A, incoming lugs rated 800A and vertical sections with vertical busses of 600/300A. I've never used anything greater than that since we limit our LV motors to 200HP or less.
There may be a conscious choice in overrating the vertical bus to reduce heating, since the current density and the resultant extra heat is burden on the stab-on connectors.
 
Status
Not open for further replies.
Top