I have a walk in cooler I wired, needed a 3phase 20 amp line to the compressor, draws 12 amps, and it needed a 20 240v line to the fan coil unit. The fan coil unit draws 3.3 when the fans are on and 12.5 when the defrost coil is on. The refridge guy was questioning my bill as he thinks 1 circuit would have done it all. Now I know the compressor draw and the fan draw would not overload the breaker but taping of the 3 phase line for single phase sounded odd to me and something I would never think to do. He says they do it all the time and most electricians don't know how to wire the refridgeration stuff. Anyone have input on this? Thanks.
Maybe I do things wrong also, for I am with you. I tend to look at the 50% rule (NEC 2005 210.23), but that only applies to not fastened in place equipment. Based on 440.34 I feel their method is allowed though I do not do it that way. Sometimes I note that I do not do things the cheapest or the best.
I would be interested to know if someone else could show that the single circuit method were not allowed, but right now I don't see it.
P.S. Buffalo him by telling him that refrigeration equipment confuses the electrons in single circuits. The cold ones from the fan unit run into the hot ones from the compressor and they just end up bouncing back and forth with a period of 16.7 milliseconds (60 Hz), creating a changing magnetic field.
Most electric defrost fan coil units are designed so that the heaters will not operate when the compressor is on. The defrost time clock will open, de-energizing the liquid line solenoid. The compressor will pump down and when it's contactor opens an auxiliary contact will close allowing the heaters to work. After defrost is over the compressor starts up again but there is usually a fan delay to keep the fans from coming on until the coil is frosted.
If the system is designed like this the defrost load and the comp/fan load will not be energized at the same time.
The main disconnect would be sized for the combined comp/fan load and would handle the resistive load without a problem.
If I knew how to do it I would post a generic version of the way my company does it.