High Bay LED Voltage Drop


Senior Member
Have a new warehouse that im using some LED high bays in. Im hitting a small 30 kVA step-up transformer to take the voltage from 120 to 277 to serve these lights. Im putting (12) on a circuit and they are 241 watts each which comes to 2892 watts / circuit or 10.4 amps. On a #12 wire running 400 feet im getting around a 6% voltage drop depending on the power factor I use.

The local energy code limits the voltage drop but I cant remember what it is for branch circuits so this may be a non-issue.

My question is, how will these lights respond to a 6% VD? I can easily go to a #10 wire but it seems like that would quickly eat away at the savings for the LED lights and extend the payback period. I would also prefer not to add another circuit due to the preferred switching arrangement and cost of another run from electric room.

Side question, what is a good power factor to use for LED lighting?

Thanks and Happy Sunday.


I may be missing something but I don't see how Power Factor is related to voltage drop?

In any case I think is common to see a working rage of +/-10% on the input voltage of these LED modules, should be stated on the units.

Power Factor could be estimated from the input voltage, current and power ratings of the modules. PF=Power/(V*I).


Senior Member
Springfield, MA, USA
Electric motor research
Power factor relates to voltage drop because lower power factor means more current (and thus more voltage drop) for a given power level.

The answer for your application will really depend upon the specifics of the fixtures that you are using.

For example:

These are specified to have a power factor of >0.9 and a voltage rating of 120-277V. The wide voltage range is the key issue here; these are _constant power_ loads. As the voltage drops, the current that they consume _increases_ to maintain the same power level.

The net result with these specific LEDs is that with a 277V supply, you could have huge (>50%) voltage drop but maintain full light output. The voltage drop would, however, show up as reduced efficiency and increased power consumption.



Senior Member
Jon's point is a good one from an operational /practicality perspective, but if you are held to a voltage drop limit in a code, as most of us are (Energy Code), you need to limit it to that amount.