Voltage drop calculation for Feeder 2% or 3%

[Hameedulla-Ekhlas]

Greeting, I have faced one problem with voltage drop calculation in feeder. In NEC-2008 it is not clear the voltage drop for feeder. NEC states " voltage drop for branch should not exceed 3% and the total voltage drop for branch plus feeder is 5%".
In large distribution projects, I am really confused because the voltage drop for branch can never exceed of 2% for dwelling unit and now for feeder can I take 3% which makes the total 5%. It has really great impact on cable sizing for large distribution as well as economics.

So, Can any body help me in this issue. :-?

best regards
Hameedullah Ekhlas
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[raider1]

Welcome to the forum.

The voltage drop recommendations in the 2008 NEC are found in fine print notes to 210.19(A)(1) and 215..2(A)(3).

Fine print notes are not enforceable as code and therefore are just recommendations.(See 90.5(C)

Also the recommendation is for feeders or branch circuits to have no more than 3% and the combination of the 2 to be no more than 5%.

Chris

 

[birtclp]

Above is correct for NEC, but here in SC we have been hit with another code addressing voltage drop...the Energy Code (ASHRAE 90.1-2004).

8.4.1.1 requires feeder conductors to be sized for a maximum voltage drop of 2% at design load.

8.4.1.2 requires branch circuit conductors to be sized for a maximum voltage drop of 3% at design load.

May not apply where you are working, but does apply in many states in US and for Federal Government work.