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

[Allen Frishman]

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 - cell
(888) 460-2867
www.aeonsolar.com


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