Main distribution panel

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Matt Mckenzie

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What is the "MINIMUM" size main overcurrent protection device required by code for a main breaker distribution panel with a 795 amp load? 600 or 800? Please help. You go to the next higher size OCP but this is asking for minimum......
 
Matt Mckenzie said:
What is the "MINIMUM" size main overcurrent protection device required by code for a main breaker distribution panel with a 795 amp load? 600 or 800? Please help. You go to the next higher size OCP but this is asking for minimum......
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Calculated load (including 125% for continuous or other adjustments for motors) or measured load?
You cannot just size the breaker for the measured load, but that would indeed be a minimum.
Nor can you add up the numbers for all of the load breakers, since that would be too high a number.
 
Matt Mckenzie said:
What is the "MINIMUM" size main overcurrent protection device required by code for a main breaker distribution panel with a 795 amp load? 600 or 800? Please help. You go to the next higher size OCP but this is asking for minimum......
Click to expand...


Matt I am trying to understand how a 600 amp overcurrent protective device would not trip with a load of 795 amps. Even if that is the calculated load you have to go to 800 amps.
 
Matt Mckenzie said:
What is the "MINIMUM" size main overcurrent protection device required by code for a main breaker distribution panel with a 795 amp load? 600 or 800? Please help. You go to the next higher size OCP but this is asking for minimum......
Click to expand...
Is there ever a "MINIMUM" size OCPD specified for anything in the NEC? The NEC requires MINIMUM CONDUCTOR sizes, and MAXIMUM OCPD sizes, but as far as I know, if you want to put a 300A breaker on a 795A expected load, that's your prerogative. Now that said, the load size will dictate the minimum conductor size, which may be too big to actually CONNECT to a 300A breaker and besides, we all know that's a gross overstatement, I'm just pointing out that the way the question was worded and emphasized, there is no valid answer. I might be wrong though, I've never actually checked.
 
Jraef said:
Is there ever a "MINIMUM" size OCPD specified for anything in the NEC?...
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YES.

For starters, 210.20(A) and 215.3 both state in part, "the rating of the overcurrent device shall not be less than the noncontinuous load plus 125 percent of the continuous load." That stipulation amounts to a minimum OCPD rating.
 
Matt Mckenzie said:
What is the "MINIMUM" size main overcurrent protection device required by code for a main breaker distribution panel with a 795 amp load? 600 or 800? Please help. You go to the next higher size OCP but this is asking for minimum......
Click to expand...
The minimum OCPD rating is the noncontinuous calculated load plus 125 percent of the continuous calculated load.

The above statement is based on 230.41(A)(1), but 230.42(A)(3) is an option seldom used.
 
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