[RE-wrenches] Main Service Fuse rated higher than Bus Rating of attached sections?

[Mark Frye]

NEC 2008, 240.21 (B)(1)(1) a.

Each of the smaller buss sections are feeders which are sized according 
to the tap rules. I believe the answer to your question is that the 
larger fuse can't protect the smaller buss. *But*, the likelihood of a 
short developing in that section of the circuit is very small and if one 
did, damage to the equipment would be limited that area. This is the 
essence of allowing taps.

Mark Frye

On 2/17/2015 6:17 AM, Allen Frishman wrote:Wrenchers,
> I run into lots of Service Equipment that has a Large Service Switch 
> which feeds multiple Sections with the Bus bar on each section rated 
> significantly less than the main bus.    A specific example that I am 
> currently looking at has a 4000Amp Switch with a 3500 Amp Fuse which 
> feeds 3 (1000 Amp) switchgear sections.     How is it possible that 
> the 3500 Amp Fuse protects the (3) 1000 Amp Sections?    In this 
> particular case each of the 1000 Amp Sections has between 3 and 6 
> fused switches on them.     The sum of those switch/fuse ratings 
> exceeds 1000 Amps in each case.    For reference - This service gear 
> is over 40 years old.
>
> All thoughts are appreciated.
>
> /Al Frishman/
> AeonSolar
>
> /(917) 699-6641 <tel:%28917%29%20699-6641> - cell/
> /(888) 460-2867 <tel:%28888%29%20460-2867>/
> /www.aeonsolar.com <http://www.aeonsolar.com/>/
>
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