serie rating of MCCB

[tem1234]

Hi,

We have a place with a lot of MCCB Westinghouse type F and FB and some Cutler-Hammer type FD and FDB.

The capacity of these breaker are 14 or 18 kA, but the short-cicuit current is way over.

The breakers are in serie with a current limiting fuse, type RK-5.

I have found serie rating chart for the Cutler-Hammer breaker with the fuse, but not for the Westinghouse.

Does anybody have this information available?

Thanks

 

[Live2learn]

I do not think current limiting fuses will get you there. You also can not ride the fuse curves for current limiting capability. I guess you can if you REALLY have to, but the dynamics of breakers opening and the fuse reaction to it has to be tested and confirmed. That is why when series ratings first started getting published, better than half of the combinations tested with fuses did not pass.
looking at the fuse curves, it appeared that the fuses would limit the fault current, but the dynamic impedance imposed when the breakers started to open ruined that thought process.

 

[tem1234]

Hi Live2learn,

Do you think that we cannot rely on this kind of chart?

 

[Live2learn]

yes I do believe you may use that chart only if they are for those circuit breakers listed in those combinations. For your westinghouse circuit breakers I would get in touch with the manufacture to get a hold of the necessary information.

 

[davidbeach]

You're SOL. If a series rating existed for the F or FB breaker it would be on that chart as Cutler-Hammer took over all of the Westinghouse low voltage product line.

 

[dpc]

David's probably right. Eaton/Cutler-Hammer would be the ones to advise you on any series ratings available for the old Westinghouse breakers. But from their perspective, why would they take on that liability for an old product?



David Castor

http://www.cvoes.com

 

[jraef]

The concept as it applies now was not on the radar in the Westinghouse days. So why would Eaton do retro-active series ratings on a product they make no money on when they could just as well sell you a new breaker with the proper ratings?

"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> faq731-376

 

[tem1234]

Thanks for your reply,

I was thinking maybe someone have old litterature about this.

I think that it wasn't a bad conception at the time and people really take short circuit current into consideration. That's why they put current limiting fuse in serie, but without any written information I can't really make assumption. But maybe in the old days testing wasn't done for this setup like today as jraf said. Maybe they only made some calculation?

If it was a couple of breaker i wouldn't mind, just change it. But here are several hundred.

 

[rbulsara]

There were and are no accepted method of "calculating" series ratings. They have to be tested combinations. Applying CLF can be a better than nothing approach but they can't be relied upon.



Rafiq Bulsara

http://www.srengineersct.com