408.30 Meaning of "minimum feeder capacity for load"

[xguard]

I've seen a few threads debating this but there doesn't seem to be a general concurrence of it's meaning.

IMO:

"408.30 - All panel boards shall have a rating not less than the minimum feeder capacity required for the load calculated in accordance with Part III, IV, or V of article 220, as applicable" means I determine the load based on 220, applying demand factors, then I go to 215.2 "minimum rating and size" to determine the minimum feeder capacity based on this load.

Example

Load with demand factors applied:
99 AMPS non-continous
100 AMPS continuous

Feeder capacity = 99 + 1.25x100

as opposed to 99 + 100

BUT - this is only for the rating of the panel board, not the OCPD (MCB in my case), which doesn't seem to need to be based on the 1.25 for continous loads from what I can find.

Thoughts? Votes? References?

 

[david luchini]

I've seen a few threads debating this but there doesn't seem to be a general concurrence of it's meaning.

IMO:

"408.30 - All panel boards shall have a rating not less than the minimum feeder capacity required for the load calculated in accordance with Part III, IV, or V of article 220, as applicable" means I determine the load based on 220, applying demand factors, then I go to 215.2 "minimum rating and size" to determine the minimum feeder capacity based on this load.

I read 408.30 as requiring the panelboard to have a rating not less than the load as calculated in Art 220. In your example, that load is 199A. (408.30 doesn't direct you to Art 215, as I read it.)

But that is only half of the equation...

Example

Load with demand factors applied:
99 AMPS non-continous
100 AMPS continuous

Feeder capacity = 99 + 1.25x100

as opposed to 99 + 100

BUT - this is only for the rating of the panel board, not the OCPD (MCB in my case), which doesn't seem to need to be based on the 1.25 for continous loads from what I can find.

Thoughts? Votes? References?

215.3 requires the feeder OCPD to be not less than the non-continuous load plus 125% of the continuous load. In your example, that would be 225A minimum. 408.36 requires that the panelboard be protected by an OCPD having a rating not greater than that of the panelboard. If your protection is 225A, that would force you to make the panelboard rating 225A or greater. So for a feeder supplied panelboard, the rating would end up being not less than 125% continuous plus non-continuous anyway.

I think 408.36 Ex No. 1 would allow a service supplied to be sized at 100% of continuous plus non-continuous load.