208/120 3 phase 4 wire panel

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mmcampbe

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I have panel installed that is a 208/120 3 phase 4 wire panel being used primarily for 208V equipment. It has a "max amps" of 225A.

Is this the max current on the feeding cables or between the phases?
 
Can't really say with the limited info.

The panel may be rated 225 amps but you did not say what the feeder supplying the panel is capable of.

The feeder might only be 100 amps.
 
I would say if the panel is rated for 225 amps, that would be the maximum main disconnect ocp allowed in that panel. That would be a 225 amp 3-pole breaker. Correct me if I'm wrong. The feeders would have to be sized according to the size of the main disconnect breaker. So if you only need a 150 amp service then you would put in a 150 amp main 3-pole breaker and size the feeders to 150 amps. You don't have to use the full capacity of the panel.
 
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I would say that, unless we're talking taps here, that the breaker supplying the feeder is what must be sized to protect the feeder, main breaker or not. The maximum combination of breaker/feeder rating must be limited to 225a due to the panel's rating.
 
Actually the maximum ocp device (breaker or fuse) protecting that panel can not exceed 225 amps for that 225 amp rated panel. You can make the feeders as large as you want. Over-sizing the feeders only reduces resistance, it doesn't increase the amount of current. If the feeders were rated for an ampacity lower than that of the panel you would have to reduce the ocp device down to the rating of what ever the feeders actually are. So if the feeders were 10 AWG the max. breaker would be 30 amp. If the feeders were 750 KCmil the max. breaker protecting that panel would be 225 amp since that is the max current allowed to travel thru that panel. There is no min current allowed to pass thru the panel. NEC dictates the minimum size conductor, not the maximum size conductor.
 
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adrian33773 said:
Actually the maximum ocp device (breaker or fuse) protecting that panel can not exceed 225 amps for that 225 amp rated panel. You can make the feeders as large as you want.
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Of course; poorly worded.
 
adrian33773 said:
I would say if the panel is rated for 225 amps, that would be the maximum main disconnect ocp allowed in that panel. That would be a 225 amp 3-pole breaker. Correct me if I'm wrong. The feeders would have to be sized according to the size of the main disconnect breaker. So if you only need a 150 amp service then you would put in a 150 amp main 3-pole breaker and size the feeders to 150 amps. You don't have to use the full capacity of the panel.
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The panel is fed from a 100 amp Meter but this can all be upgraded easily (It's in a substation and I work for the utility). What does OCP stand for? I'm assuming it is the main breaker on the panel.

Thanks for your help guys.
 
mmcampbe said:
What does OCP stand for? I'm assuming it is the main breaker on the panel.
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?Over Current Protection.? Sometimes a "D" for "Device" appears as well (i.e., OCPD). It might mean the main breaker on the panel or the breaker supplying the feeder. It depends on the context of the sentence.

mmcampbe said:
Is this the max current on the feeding cables or between the phases?
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It does not make physical sense to speak of ?current between phases.? Current flows out of a panel on one phase conductor, and after having passed through the load it flows back into the panel on another phase conductor. But current is measured as it passes through any single conductor, not from one conductor to another.

The 225 amp rating is the maximum amount of current that can be allowed to flow on any of the three phase conductors.
 
charlie b said:
The 225 amp rating is the maximum amount of current that can be allowed to flow on any of the three phase conductors.
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. . . or even two or all three simultaneously.
 
charlie b said:
The 225 amp rating is the maximum amount of current that can be allowed to flow on any of the three phase conductors.
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LarryFine said:
. . . or even two or all three simultaneously.
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The 225 amp rating is the maximum continuous current allowed per pole. Current exceeding the rating is permitted for short durations, such as motor starting or transformer in-rush.
 
Actually check the switch gear to find out what is feeding your panel --fuse protection. If 225 amp fuses are are being used than you are covered at 225 less 80% between phases so (225amps * 80% = 180amps)

I motors are being fed check percentage of use in chapter 450 motors.
 
oscarmal said:
Actually check the switch gear to find out what is feeding your panel --fuse protection. If 225 amp fuses are are being used than you are covered at 225 less 80% between phases so (225amps * 80% = 180amps)
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I don't follow you.

225 amp fuses or breakers will still require 4/0s and both are fine for a 225 amp rated panel.
 
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