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ekstra   ara
 Post subject: Available fault currents and under rated equipment
PostPosted: Fri Jun 11, 2010 10:00 am 

Joined: Sat Mar 06, 2010 6:07 am
Posts: 8
This might be a stupid question but I want to cover any exceptions to something that is quite clear to me as a problem.

We had a SC/AF study performed for a customer of ours by an engineering firm. During the equipment labeling phase we confirm the equipment is rated for the calculated fault current that is available as we affix each label.

The customer's 480V 2500A bus duct riser has fault current upward of 60-70KAIC calculated on the floors. We discovered many of the fused bus duct disconnects serving Siemens S2 480V panel boards with ED4 circuit breakers have NOS 200A (one time fuses) rated for 10KAIC.

To me this is an issue. My solution would be to install current liminting J fuses in the disconnects and they would series rate with the ED4 breakers and problems would be solved.

Before I make this solution suggestion are there any exceptions I am not aware of?

If the 2500A Bus Duct riser fuses are current limiting KRP-C, from what I understand the let through current is still greater than 10KAIC so to me this is still an issue with the bus duct switch fuses.

Are our findings valid?

Thanks for your help.


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PostPosted: Fri Jun 11, 2010 10:18 am 
Sparks Level

Joined: Mon Mar 29, 2010 11:52 am
Posts: 110
Location: Yankton SD/ Lead SD
You will have to follow the quidelines in NEC article 240.86.


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PostPosted: Fri Jun 11, 2010 10:26 am 

Joined: Sat Mar 06, 2010 6:07 am
Posts: 8
240.86, A, B, and C noted.

As well as 110.22.

Thanks.

Will


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