Can someone think of a way to REDUCE the HIGH ARC FLASH numbers for this design? 2

[bdn2004]

We've a customer that recently purchased a new MCC: Allen-Bradley 2100 Centerline. It is fed by a captive 2000kVA, 480V transformer that they own also. Per our software there are 65 calories at the incoming MCC terminals - Extreme Danger.

The customer bought a main circuit breaker for the MCC with a maintenance mode switch, but the MCC is not arc protected gear and the bus therefore shares the same air space as the incoming, rendering the main worthless as a protection of arc flash for the entire MCC. That's our understanding anyway.

It's been suggested to install 2000A fuses in a remote location between the transformer and the MCC. That's a costly option.

Does anyone have any thoughts on how to remedy this ?

 

[bdn2004]

Yes the Utility provided the S/C and X/R that's used in the Easy Power model for the Utility.

I think you have to order the Centerline MCC with arc shield option? A guy working on this contacted Allen-Bradley to see if the arc stuff could be added. The answer was no.

We usually put the bus at the top of the MCC, because most of the MCCs we see are 20+ years old and none have arc resistant anything. That gives you a place to analyze the MCC at the worst case place and no worries that you've included the main breaker.

We've got the unlimited bus package from Easy Power. Worrying about bus count is not really an issue anymore that I can tell until you get thousands.

The bus differential idea is good one. Have you seen that on 480V ?

And the NEC Code...I hope the engineering firm thought about that. Cause that is a long way between the transformer and the MCC. It's relying on the primary protection only. But it is in an industrial plant...and all the various exceptions may apply.

 

[nhcf]

in the context of an arc flash study, how does the arc-shield MCC affect the IE levels? Does it allow you to credit the main circuit breaker? Does it allow for reduced IE levels at the bucket due to its construction? While it is likely safer, does it buy you anything when performing an analysis per IEEE 1584 vs a standard MCC?

 

[dpc]

in the context of an arc flash study, how does the arc-shield MCC affect the IE levels?

If the gear has been tested to contain arcing faults within each individual section, then I'd include the main breaker in the arc flash calculation for the remainder of the MCC. If all sections are arc-rated, then there is no significant arc-flash hazard IF ALL DOORS ARE CLOSED and LATCHED. Once a door is opened, it's a different story. Just my opinion, of course. The standards are not specific on many of these issues - requires engineering judgement.

 

[nhcf]

Thanks DPC- that makes sense.