MCCB single pole ratings

[alehman]

UL 489 and IEC (I think) specify single-pole full voltage short circuit test current for three pole molded case circuit breakers which are much lower than the 3-phase interrupting rating. For example, 1200A frame 3-pole breakers are tested at 12.1kA for full voltage across one pole per UL, regardless of the marked AIC rating.

Corner-grounded systems require the ability for any one pole of a 3-pole breaker to interrupt faults at line-to-line voltage and 87% of rated interrupting current. Does anyone know of a manufacturer of MCCBs tested or rated for line-to-line voltage across a single pole?

 

[busbar]

See page 3 or

http://www.eatonelectrical.com/unsecure/cms1/LT08703009E.PDF

The 12.1 and 8.66kA single-pole ratings are discussed; dated 1/95.

 

[dpc]

You might want to check with Square D. I seem to recall that their breakers are tested for this.

 

[busbar]

It may be worth mentioning that, besides corner-grounded systems, midtap-grounded 480?/240-volt and 480-volt high-resistance-grounded systems also need the single-pole overcurrent withstand ratings applied.

Another related caveat is that 300-volt fuses applied to a corner-, midtap- or resistance-grounded 480-volt system is also a serious misapplication.

 

[alehman]

Thanks. I'll give SqD a call. This is an installation that one of my clients just finished. The breakers are GE type SKLB.

I think in the case of resistance-grounded or ungrounded systems, the situation can only occur if there are two L-G faults with one upstream and one downstream of the breaker.

 

[jbartos]

Suggestion: Visit

http://www.ecmweb.com/ar/electric_understanding_circuit_breaker/

for Understanding Circuit Breaker Marking

http://ecatalog.squared.com/catalog/173/html/sections/08/17308017.html

for c UL Listed for use on 240 V Corner-grounded Delta Systems (Grounded B Phase)
(look for red "c&quot