Apmccandless
Active Member
I work for a small private school. Recently we purchased 3 Dds 9800 dimmers from a local theatre. My question is about power supply conductors. The school electrician is going to be wiring them into a portable rack. After consulting with him we have different understandings of what gauge power conductors are required for this purpose. The building is wired with a 3 phase 120/207 5 wire company switch (400) amps. The plan we decided on is to wire each dimmer to 2 phases of power. So dimmer one would be phase a and phase b, dimmer two would be phase a and phase c, dimmer 3 would be phase b and phase c. Which brings me to my question, my understanding of the NEC is that we are required in this situation to supply the 2 phases of power in each dimmer with wire to accommodate 80 amps per phase (per the manual) and neutral to accommodate the sum of the power of the two phases (160 amps) because it will be run on 3 phase power. The school electrician says that the NEC only requires 130% of the amperage of a single phase because that is the most that can be drawn by the neutral in 3 phase power with SCR dimmers. My question is only in regard to the wiring in the rack (from dimmer to camlok) not to the feeder cable supplying the rack. Normally I trust the school electrician he has been a valuable resource but I know he is not as knowledgeable about the theatre sections of the NEC as some of the posters on this forum. Thank you in advance for your help.