Voltage drop (actual load vs calculated load)

Tainted

Tainted

Senior Member
Location
New York
Occupation
Engineer (PE)
If I do a load calculation per article 220 for an apartment load, the load comes out to be 175 amps.

Do I size voltage drop based off 175 amps or the actual load?

I doubt that the apartment will ever use the full 175 amps and the code calculations are very conservative.
 
If I were sizing voltage drop for a feeder in my own home, I'd probably use 1/3-1/2 of the article 220 calculated load for the continuous loading, and probably estimate the largest inrush load to calculate voltage drop for things such as flicker.

But if I were sizing voltage drop for a feeder for something like an energy code, I'd read that code very carefully to see what they say about _how_ to calculate the voltage drop. Do they give me wiggle room to estimate the actual current draw, or do they require me to use the article 220 calculated current?
 
I personally tend to use the larger wire size if the Vdrop is close. California has Vdrop requirements in the efficiency code but I don't think I have ever been called out for it being too high.

~2.5% I will go next size up. I use calculated load. It is hard to argue on plan check to use anything less than calculated load. It kinda depends on what the feeder is going to be for. For a motor load where there is a fused disconnect I might allow a little more. But usually for a panelboard feeder I stay on the lower side of Vdrop.
 
ptonsparky said:
How will you know what the actual load is going to be? At 2 AM or 6 PM?

You will need to clarify with whoever is asking.
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You can say that with anything though even of you calculate according to code.

winnie said:
If I were sizing voltage drop for a feeder in my own home, I'd probably use 1/3-1/2 of the article 220 calculated load for the continuous loading, and probably estimate the largest inrush load to calculate voltage drop for things such as flicker.

But if I were sizing voltage drop for a feeder for something like an energy code, I'd read that code very carefully to see what they say about _how_ to calculate the voltage drop. Do they give me wiggle room to estimate the actual current draw, or do they require me to use the article 220 calculated current?
Click to expand...
If code does not say to use the calculated article 220 amperage then it shouldn’t be a problem estimating the voltage drop based on half the calculated current from article 220
 
ptonsparky said:
The NEC does not tell you how to calculate for VD. VD is a fine print note.
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yea but energy code and NYC makes it a requirement. But again, they don't tell you if you have to use actual amperage demand or the amperage calculated from article 220
 
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