VD: 2% plus 3%

[xptpcrewx]

I was referring to this table in particular...

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Note: The total allowable voltage drop could be considered the difference between minimum service voltage and minimum utilization voltage (as a conservative approach). Whether or not to use Range A or Range B depends on the duration of voltage fluctuation expected. For steady-state applications I would use Range A; for transient motor starting perhaps Range B.

 

[xptpcrewx]

Do you include the service conductors as though they were "feeders" in the context of the the NEC guidance that says 2% VD on feeders plus 3% VD on branch circuits provides for reasonable efficiency of operation? I am having a disagreement with a client on this question.

No, because ANSI C84.1 recommends the electric supply system be designed and operate within a specific nominal voltage range. Service voltage fluctuations must be limited in extent and duration to prevent equipment damage/misoperation. To consider service conductors or the effect of the utility transformer in your voltage drop calculation would be redundant as they are part of the electric supply system.

However, if you are doing a load flow study and want to determine the voltage profile throughout the facility, service conductors, utility transformer and upstream system impedance will obviously need to be considered. For purposes of complying with acceptable voltage drop, the method I am suggesting is a conservative (worst-case) approach which should give adequate results given limited information. If you use the minimum service/utilization voltage, you can always fall back on ANSI C84.1 as a reasonable justification.

Lastly, using measured values taken at a particular day, at a particular time, under particular load conditions is sloppy/erroneous in my opinion and is subject to further deviation depending on the utility switching configuration and the time of year.