Multi wire circuit voltage drop

[GSXR600]

Hi when performing a voltage drop calc on a 3P 4W multi wire branch circuit should it be calculated as a three phase circuit?

 

[Smart $]

Hi when performing a voltage drop calc on a 3P 4W multi wire branch circuit should it be calculated as a three phase circuit?

It can be, but there is no clear-cut rule. A lot depends on each sub-circuit's purpose, whether an unbalanced load, and the likelihood of non-simultaneous use.

For example, balanced banks of lighting that will under normal use be on or off simultaneously can be calculated as a three phase circuit.

Where sub-circuit loads will be energized at random instances, calculate as though single phase two-wire circuits (each L-N, even though N is shared), but only to determine if the voltage drop using wire sized per a three phase voltage drop calcualtion would yield a single phase voltage drop that would decrease performance beyond an acceptable level. The difference in volts dropped for the same size wire will be the ratio 2:1.732 or vice versa.