UL891 - Mini Ciruit Breakers

[cmahaffey]

Guys,

I have a question for anyone with UL expertise. I am modifying a IEC based switchboard design to pass UL891 here in the States. The IEC design allows multiple Mini-Circuit Breakers (UL 1077 "supplementary protective devices") to be tapped downstream of our incoming Utlity/Genset breakers (4000A, 100kAIC). This is a "no-no" for UL (dang product liability laws in the US!).... ABB does make UL 489 ("branch circuit protective") Mini-Circuit breakers, but they are only rated at 10kAIC. Does the fact that these MCBs are UL 489 branch circuit rated all us connect via a bus tap even though the bus is rated 100kAIC? The obvious solution is to use fuses, but our UPS system MUST know the status of the breaker/fuse. They do not make fuse blocks with "blown-fuse" auxiliaries that I know of...Anyone have any thoughts, suggestions??

As always, any help is greatly appreciated.

Colin

 

[dpc]

Do a little searching for "series-rating" in UL MCCBs. You can put two breakers in series to increase the effective interrupting rating of the downstream device where they are a tested combination. Normally, this means that the two breakers must be the product of the same manufacturer.

Of course this means that the two breakers will not coordinate at high levels of fault current.

Are these smaller breakers in the same enclosure as the 4000 A breaker? If not, conductor sizing must meet NEC.

BTW, I believe there are fuse holders that will provide microswitch contact output based on fuse status. You might check with Bussmann.

 

[jraef]

I don't know of anyone that has series ratings on MCBs like you are describing, they are still basically IEC devices that have been adapted and the UL489 ratings on them are relatively new, so nobody has done the required series testing yet. But you probably can do what dpc says using "old fashioned" UL489 MCCBs of the type we have all been using here in the US for decades. Like he said, check with the manufacturers. I know you can do series ratings with Siemens, but I'm not sure if anyone can get to 100kAIC on a small breaker like that even in series with a current limiting breaker. Do you really have 100kAIC available, or is that just the rating of the 4000A incoming breaker?

If you really need 100kAIC, fuses are probably your only option and like dpc also said, there are BFI (Blown Fuse Indicator) fuses out there that have spring driven pins in them which activate a microswitch in the fuseholder.

 

[jraef]

More info:

http://cmsapps.sea.siemens.com/controls/speedfax07/07Speedfax_pdfs/07Speedfax_06/06_146-150.pdf

And by the way, you are going to have to know the voltage at which you want that 100kAIC, it makes a big difference.

 

[cmahaffey]

Thanks for all the help guys!

I doubt there is actually 100kAIC available, but certainly b/w 65&100kAIC, and I think UL 891 makes you rate the switchboard at the lowest kA rating of any device upstream of a PT (i.e. branch circuit protectors). Like you say, I don't think putting these in series MCCBs is very practical. Howerver, DPC led me to call Bussman, and they do have something that will work great. A new "CCP" line of fuse holders that have aux contacts for blown fuse indication (specifically for a PLC like this application)

http://www.cooperbussmann.com/2/CCP.html

Initially I called Ferraz-Shawmut directly, and the representative told me they couldn't make the "microswitch" device like you mention to pass UL specs, and that they were currently "arguing" with UL and hope to have it pass soon. I wasn't holding my breath for UL to make any sudden changes, though........ Maybe the guys was "BSing" me, but it looks like Bussman has something that works, so great!!

Thanks,

Colin

 

[dpc]

Just make sure you are covered for single phasing if a fuse blows.