Does THD affect Voltage Drop?

[Senselessticker]

I've run into a situation where I'm approaching 5% on my calc for V-Drop on a 120 single phase lighting circuit. I've learned that Compact Fluorescent Lights (CFL) generally have a power factor of 0.5 to 0.6. This, of course, drives up the current draw for each lamp. I've also learned that CFL's produce a very significant amount of Harmonic Distortion. Will the THD contribute to the voltage drop on the conductor? And if so, is there a reference somewhere that I can use as a standard to factor in the THD on the drop?

My client has yet to provide me with specific info on the exact CFL being used. But I know that they are 28 Watt, "screw in" retrofit type CFL's that replaced an incadescent bulb. To farther complicate the matter. These CFL's are in an explosion proof fixture in a Class II, Div II area. I've expressed concern over if the UL listing will still be valid with these CFL's installed in the fixture.

Getting back to the main question...will the THD effect the voltage drop on the conductor? And if so, how do I factor that into the calc?

Many thanks!!

 

[jghrist]

The THD does not affect the voltage drop because you are concerned about the fundamental frequency voltage when calculating voltage drop. Harmonic currents (frequencies at integer multiples of the fundamental frequency) cause harmonic voltages.

 

[Mstrvb19]

There is one catch-it is possible for the harmonics to deliver some real power to the cable through the voltage drop on it. If this were to increase the cable temperature, then it would also affect the voltage drop of the fundamental frequency system. However, it is rediculously unlikely that the harmonics would be significant enough for this to occur. The harmonics are far more likely to effect heating in a supply transformer, which could affect voltage drop in the transformer-just another side of the issue to consider.

 

[advidana]

For screw cf lamps check with lamp manufacture for amps and pf. For standard plug type cf in use ballast manufacure catalog data from Advance ballast or Ge Ballast or universal Ballast. these catalogs have amps and pf listed for ballasts with lamps attached. Use largest amp draw worse case pf if information is unknown. For lighting harmonics load-design for about 60 to 65 of wire/breaker size or use oversized neutral wire for these type of lighting circuits. There is a lot of information available. you just need to go out there as start digging like the rest of us.