5% Voltage drop on 3 phase

[AusLee]

Hi,

A street lighting circuit, with single phase fittings but connected to a 3 phase supply. Each next fitting is on a different phase, overall reasonably balancing the neutral.

The question is: the code allows 5% voltage drop. Now i'm looking at this as follows: the fitting is single phase, rated 230V, so it can tolerate as per its appliance standard a maximum Vd of 5%, that it 5% off 230V = 11.5V or 218.5V minimum at the last fitting.

Someone is saying that because it's a 3 phase circuit, you're allowed 5% off the 400V (three phase for 230), which means the margin is 0.05 * 400 = 20V. I'm thinking this is an abstract number that does not correspond to anything. If it was a 3 phase load then yes it would be accepting a 380V minimum, but all loads are single phase.

Can you please advise: 5% is off 230V or 400V on a 3-phase circuit of single phase devices?

Cheers!

 

[LionelHutz]

Since this is your own system you're actually allowed whatever voltage drop you find acceptable so the lights will still operate.

It's the same number. On a balanced system, a 20V drop measured phase to phase is an 11.5V drop measured phase to neutral. "Someone" forgot about the sqrt(3) factor.

 

[waross]

What Lionel said. 5% of 230V on 230V circuits, 5% of 400V on 400V circuits.

Bill
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