Voltage drop calculation for feeders to a load panel

[mshader7]

All,
All other conductor sizing requirements aside, At a load panel with multiple loads.
To correctly size the feeders for voltage drop to the panel, does one use the sum of all loads at the panel or the largest load at the panel.
I perhaps have needlessly twisted myself into a pretzel over this.
Thanks in advance for comments

 

[iwire]

For the most part it is just another design choice.

My opinion would be to figure it for the largest current flow expected under normal conditions. If you wanted to leave some headroom for future loads would be just another deign decision based on the specifics of the job and budget.

 

[GoldDigger]

If (some of) the loads are motors, then you have two separate concerns:
1. Supplying the sum of all the loads that are likely to be on at the same time, AND
2. Supplying the starting current for the largest motor at the same time.
You are usually safe in assuming that not all of the motors are going to start at the same time, and that is why the code tells you to consider just the largest motor differently.
For non-motor loads, you would treat them all equally.

Given that you are looking specifically at VD, you need to look at the steady state VD and also at the transient VD from motor starting. That surge current's effect on voltage to other loads is where you would look specifically at the largest motor, or the one with the largest surge if they are different types.

Tapatalk...

 

[mlnk]

I figure voltage drop based on the circuit breaker for the feeder. A 100 amp sub panel may have only 50 amps of load now, but I use the 100 amps for VD calcs. i think that is what an AHJ would want.

 

[ActionDave]

I figure voltage drop based on the circuit breaker for the feeder. A 100 amp sub panel may have only 50 amps of load now, but I use the 100 amps for VD calcs. i think that is what an AHJ would want.

To each his own.

For the most part it is just another design choice.

My opinion would be to figure it for the largest current flow expected under normal conditions. If you wanted to leave some headroom for future loads would be just another deign decision based on the specifics of the job and budget.

This approach makes much more sense to me and is the one I would use.