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 Post subject: Cable Limiters
PostPosted: Tue Sep 09, 2008 6:20 am 
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Posts: 9
Can cable limiters be used to reduce the fault current levels and thus allow for smaller KAIC rated circuit breakers?


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PostPosted: Wed Sep 10, 2008 3:36 pm 
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Location: Scottsdale, Arizona
This would fall under NEC 240.86 Series Ratings which allows both tested combinations of devices for series ratings as well as series ratings under engineering supervision in existing installations (with specific provisons).

Series ratings - what you are asking about - have an odd history. I was involved with a bit of the history way back when I was at Square D in the early 1980's. At one time, series ratings were determined by fuse let thru curves. This generally worked out but a bit of controversy errupted about the application methods (I won't go into it here but it was quite an interesting time). Eventually let thru curves were not used as much but actual tested combinations of devices were used instead (combinations were listed in tables created by the manufacturers) These tested combinations were developed in conjuction with Underwriter Laboratories.

Requiring all series ratings to be tested combinations later lead to a question/problem with older installations where series ratings were needed but the older equipment was never part of the testing program (Like your case??) Because of this problem with older/existing equipment and series ratings, the NEC was revised to allow the use of series ratings of components "selected under engineering supervision"

So the long answer to your short question is yes it is possible that the limiters could protect dowstream breakers but someone (a licensed Professional Engineer according the the NEC) will have to perform an analysis to determine if it would work and then (here comes the hard part....) the P.E. must sign off and stamp it.
a.k.a. liability issue. :eek:

However, not knowing who you work for, cable limiters are often used in electric utility underground networks. - Utility transmission and distribution systems are exempt from the NEC NEC 90.1(B)(5)

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Jim Phillips, P.E.
Brainfiller.com


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PostPosted: Thu Sep 11, 2008 10:30 am 
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Thanks, Jim.


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