I need to replace 8\' 2-lamp magnetic ballast lighting with new electronic balla
ID: 1831621 • Letter: I
Question
I need to replace 8' 2-lamp magnetic ballast lighting with new electronic ballasts and t8 lamps. Existing wiring is three-phase four-wire(120/208) with three circuits sharing a common neutral. Existing loads are 12 fixures, per circuit, with a load of 16 amps on a 20 amp circuit. This amounts to 80% continuous load, on a 20 amp breaker( allowed by NEC) rows of fixtures are fed from a main conduits with twelve circuits per conduit(12 ungrounded conductors, 4 grounded conductors and one grounding conductor).with what i know about non-linear loads this could be a problem. Any solutions out there????Explanation / Answer
Three-phase, 4-wire power systems used to supply nonlinear loads cause a distortion of the phase and neutral currents, producing unwanted and potentially hazardous harmonic currents on the neutral. Nonlinear loads cause the neutral to carry as much as twice the phase current. The NEC contains no rules on sizing of branch circuit neutral conductors for nonlinear loads. Harmonic currents are present only in three-phase 4-wire Wye systems such as 208Y/120 volt systems, for branch circuits you can reduce the heat on the neutral by installing separate grounded conductors for each phase or doubling the neutral conductor size