Conductor Sizing and Voltage Drop

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JBZE

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I am sizing conductors for a Freeway Lighting System in CA.
I have 25 - 310 watt lights on a 120/240 volt 1 phase 3 wire system. (lights are run on 240 volts).

My question is this: Am I allowed to downsize the conductors as the circuit gets farther away from the service point and the load (current is smaller).

I calculate about a 5% voltage drop with a #1/0 wire for part of the system. Do I have to use the #1/0 wire through the entire circuit or can I down size the conductor as the load drops farther from the service point. It would seem overkill to use say a #1/0 between the 24th and 25th lights on the circuit.

Any advise would be helpful.
 
JBZE said:
I am sizing conductors for a Freeway Lighting System in CA.
I have 25 - 310 watt lights on a 120/240 volt 1 phase 3 wire system. (lights are run on 240 volts).
Click to expand...

Odd system for "freeway" lighting.
After your initial VD calc. you can break these down into groups of 4 or 5 fixtures and do calcs on each group. EE's don't normally do this. Your job is to do the calc for the circuit as a whole.

Let me ask you this. If I ran #10 between the first and second fixture, then ran 1/0 to the other 23, would an electron know the difference?
 
As you reduce your conductor, the VD will increase from your original calculations. You will need to keep a close eye on that.

Of course don't reduce your conductor below the overcurrent protection for the circuit.
 
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