Voltage drop based on panel MCB size, or Panel Design Current?

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Elecestim123

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Electrical Estimator
Estimating a project with a feeder that is going to be 720' long.

Project is fully engineered, but I'm trying to verify if the engineer accounted for voltage drop properly.

Panel MCB/bussing size is 800A. Panel Design Current, per the panel schedule, is 564 Amps.

Engineer has 500kcmil aluminum conductors on the one-line, which is correct from what I'm seeing when sizing for Panel Design Current (assuming 3% voltage drop. Nothing else specified) per the southwire voltage drop calculator. However, it's not correct if sizing per the MCB. Which do I need to size for? My worry is that if they ever want to draw more current to that panel in the future, voltage drop might not account for that. I don't know if that is just a problem the future owner will have to deal with and figure out, or if I need to account for it now.

Thanks in advance.
 
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It depends on what the owner is paying for. Basing the VD compensation on the load is perfectly acceptable. If someone is looking towards the future then you can size accordingly.
 
Elecestim123 said:
Estimating a project with a feeder that is going to be 720' long.

Project is fully engineered, but I'm trying to verify if the engineer accounted for voltage drop properly.

Panel MCB/bussing size is 800A. Panel Design Current, per the panel schedule, is 687 Amps.

Engineer has 500kcmil aluminum conductors on the one-line, which is correct from what I'm seeing when sizing for Panel Design Current (assuming 3% voltage drop. Nothing else specified) per the southwire voltage drop calculator. However, it's not correct if sizing per the MCB. Which do I need to size for? My worry is that if they ever want to draw more current to that panel in the future, voltage drop might not account for that. I don't know if that is just a problem the future owner will have to deal with and figure out, or if I need to account for it now.

Thanks in advance.
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I would size for the actual expected current. The value on the panel schedule is probably not very accurate (unrealistically high) if it is derived from the NEC calculations. Depending on what the load is, I might take 66% of the NEC calculated value for a VD calc, but it depends. It is up to the person writing the check if they want to build in future loading.
 
I also corrected my original post, in case people in the future see this, so they aren't confused. Had the wrong amperage (Was looking at a different panel schedule).
 
It depends on what the spec or code requires. I agree with felon that it is likely you will never see actual load anywhere near what the calculations say it will be so basing your VD calculations on the calculated load means in practice the VD will be a lot less.
 
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