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Distribution board overload conditions

E95

Hi all,

I have a question regarding how overloads are protected against in distribution boards

For example, I have a 400A distribution board fed from a 400A MCCB, I assume that the distribution is rated for the full 400A continuously? Interestingly OMS made a comment on how distribution boards were constructed with a 0.6 diversity included so that a 400A board is actually only rated for 240A continuous, someone disputed this but there was no other response unfortunately.

Not to digress too far, assuming the thermal overload component doesn't start to operate until 600A what is protecting the board from an overload condition? Is this supposed to be by diversity calcs only?

I assume if this was the case there would be lots of incidents involving burnt switchboards, or the more obvious answer that the 400A board can take 600A for longer than it would take a typical protection device to operate?

Thanks for any responses Thumbsup

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  • 0

    I would not expect that a "400 amp" distribution board would be able to carry to  carry say 500 amps indefinitely, but I would expect it to carry 500 amps SHORT TERM for whatever time it takes for a 400 amp fuse to operate, or for a typical 400 amp MCCB to trip.

  • 0 in reply to broadgage

    That's the point, a 400A fuse won't trip at all until about 600A right? 

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  • 0 in reply to broadgage

    That's the point, a 400A fuse won't trip at all until about 600A right? 

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