I'm sure this has been discussed before, but Im bringing it up again to try to understand the reasoning. When sizing a panel's feeders do you size based on the actual calculated load or the size of the panel? In one case, say you have an actual load of 405 amps and you need to go up to a 600 amp panel. If all the spaces on the panel were completely full, I'd at first have no problems sizing the feeders for the 400 amps. But what if somebody comes along and starts changing things or the building changes its function in the future? (Are there any NEC references for this topic?)
Panel Feeders Revisited.
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Re: Panel Feeders Revisited.
I'm sure you will get far more valuable input than this ole 'spector can give, but, taking into account the numbers you posted:
(a) if your calculated load is 405 amps, your feeders would need to be sized to carry that load (not at 400)
(b) again, if the load was 405, the next size panelboard, I believe, is a 600 so that would be the buss rating of your panelboard.
(c) 240-4 tells you to protect the conductor in accordance with its ampacity and (B) allows you to got to the next higher rating (with stipulations)...
(d) 240-6 lists a standard rating at 450 amps..
so, IMHO, calculated the load (405);choose the appropriatly rated panel (600 probably);
choose the conductor (600MCM Cu), select the overcurrent device (450 amps)
Hope that helps, and is in compliance to what others here think.
I'm sure you will get far more valuable input than this ole 'spector can give, but, taking into account the numbers you posted:
(a) if your calculated load is 405 amps, your feeders would need to be sized to carry that load (not at 400)
(b) again, if the load was 405, the next size panelboard, I believe, is a 600 so that would be the buss rating of your panelboard.
(c) 240-4 tells you to protect the conductor in accordance with its ampacity and (B) allows you to got to the next higher rating (with stipulations)...
(d) 240-6 lists a standard rating at 450 amps..
so, IMHO, calculated the load (405);choose the appropriatly rated panel (600 probably);
choose the conductor (600MCM Cu), select the overcurrent device (450 amps)
Hope that helps, and is in compliance to what others here think.
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
Re: Panel Feeders Revisited.
(Aside: I was interrupted while I was typing a response. So Augie got in before me. But I'll post mine anyway.}
First: 215.2(A)(1) (2005 version). The ampacity of the feeder must be at least as high as the load. However, I would size the feeder to be able to handle the entire capacity of the panel. That is a design choice, not a code requirement.
Second: You don't get the option of only sizing the conductors or the panel at 400 amps, if you have a calculated load of 405. You might try looking over the calculation, and see if you can justify revising it to reduce the results to below 400.
As far as the NEC is concerned, the original designer need not be concerned about the impact of future changes on the adequacy of the conductors, panels, and overcurrent devices. It is the responsibility of the future designer to verify their adequacy under the proposed new configuration. That being said, a good designer will take into account the possibility of future changes, and discuss them with the owner. It may be in the best interests of the owner to install a more robust system than is required for the immediate future. But that is the owner's call, as it must be paid for out of the owner's pocket.
(Aside: I was interrupted while I was typing a response. So Augie got in before me. But I'll post mine anyway.}
First: 215.2(A)(1) (2005 version). The ampacity of the feeder must be at least as high as the load. However, I would size the feeder to be able to handle the entire capacity of the panel. That is a design choice, not a code requirement.
Second: You don't get the option of only sizing the conductors or the panel at 400 amps, if you have a calculated load of 405. You might try looking over the calculation, and see if you can justify revising it to reduce the results to below 400.
As far as the NEC is concerned, the original designer need not be concerned about the impact of future changes on the adequacy of the conductors, panels, and overcurrent devices. It is the responsibility of the future designer to verify their adequacy under the proposed new configuration. That being said, a good designer will take into account the possibility of future changes, and discuss them with the owner. It may be in the best interests of the owner to install a more robust system than is required for the immediate future. But that is the owner's call, as it must be paid for out of the owner's pocket.
sceepe
Senior Member
Re: Panel Feeders Revisited.
As usual, I agree with Charlie B. I base the decision on the following logic:
If there is little chance of future needs, I usually would install a 450A main breaker in the 600A panel with 450A wire. If owner elects to add load to the panel he will probably expect to pay for that anyway. However, if owner makes it clear up front that wants capacity for future then I go with a 600A main breaker and 600 amp feeders.
Now if changing out the main breaker will be very difficult or expensive to do in the future, (like say the feeders are 500' long) I will go with larger feeders initially. You can go with 600A feeders but a 450A main breaker as a compromise. Lastly perhaps as a minimum, if the feeder length is not to long, you can size the feeder conduit for the 600A feeder but install 450A wire and a 450A main breaker. Replacing the main breaker and the feeder wire (if short) is not too labor intensive if the pipe is already there.
As usual, I agree with Charlie B. I base the decision on the following logic:
If there is little chance of future needs, I usually would install a 450A main breaker in the 600A panel with 450A wire. If owner elects to add load to the panel he will probably expect to pay for that anyway. However, if owner makes it clear up front that wants capacity for future then I go with a 600A main breaker and 600 amp feeders.
Now if changing out the main breaker will be very difficult or expensive to do in the future, (like say the feeders are 500' long) I will go with larger feeders initially. You can go with 600A feeders but a 450A main breaker as a compromise. Lastly perhaps as a minimum, if the feeder length is not to long, you can size the feeder conduit for the 600A feeder but install 450A wire and a 450A main breaker. Replacing the main breaker and the feeder wire (if short) is not too labor intensive if the pipe is already there.
james wuebker
Senior Member
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- Iowa
Re: Panel Feeders Revisited.
If your load is 405 amps cont. (more than 3 hrs.) then you will need at less 480 amps for this load.They do make a 500 amp breaker but if you have a 600 amp panel and a chance your might need more power down the road put the 600 amp in and wire. If I remember right the price on a 500 or 600 amp breaker should be the same. Not sure about the 450 amp breaker. If you put the smaller breaker in now and need to up size if later the cost will be in your breaker unless you also have a long run on the wire. Copper not cheap anymore.
Jim
If your load is 405 amps cont. (more than 3 hrs.) then you will need at less 480 amps for this load.They do make a 500 amp breaker but if you have a 600 amp panel and a chance your might need more power down the road put the 600 amp in and wire. If I remember right the price on a 500 or 600 amp breaker should be the same. Not sure about the 450 amp breaker. If you put the smaller breaker in now and need to up size if later the cost will be in your breaker unless you also have a long run on the wire. Copper not cheap anymore.
Jim
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
Re: Panel Feeders Revisited.
I had interpreted the 405 amps from the original question as being the results of a load calculation. That would tell me that if there were any continuous loads (or any motor loads), the factor(s) of 125 percent would have already been taken into account, before the number 405 was calculated. But the question did describe the 405 amps (somewhat imprecisely) as the "actual load." So that is up for interpretation.
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