1P Voltage Drop Calc’s In 3P System

[GMichael]

Was wondering if anybody can clear up some confusion for me on voltage drop calculation in a 3P system. For discussion purposes, lets say we’re dealing with a 208v/120v, 3P 4W system.

For my 1P loads (120v or 208v), would I use a 1P voltage drop equation because they’re 1P loads, or a 3P voltage drop equation because it’s on a 3P system? Thanks.

 

[kwired]

correct for basic single or three phase loads with equal current in each conductor of the circuit

 

[mivey]

as kwired said, use the same current for all three. IOW, use the largest 1P current for all three legs so you get the most conservative drop calc. It is not like you are going to size the conductors differently.

However, you can calculate the drop in each leg and neutral for unbalanced loads but I doubt you will be needing to do that. You could calc the balanced portion then add the unbalanced portion for a rough calc or more correctly just do an "exact" calculation using a matrix solution. The load power factors would matter if you want the "exact" solution.