I'm having my Electrician wire 9 1.5HP 3Phase roof fan motors. There is a little problem. My boss wants me to have the motors wire this way. From a 60amp breaker go to a Motor Stater with 10amp heaters then to a service disconnect switch then to the motor but from the first Motor Stater he want to branch to the next motor starter and from that one to the next one and so on. Is this legal?
A motor or wiring ground or phase fault (downstream of the overload relay) may cause one or more heaters to open like fuses, presenting an immediate fire hazard.
[When overload-relay heaters melt open, the overload relay is considered to be damaged beyond repair and replacement of the heater (only) is an unreliable fix. Damage from a heater fusing open has likely cooked the relay internals, reducing or disabling its function.]
[This message has been edited by Bjarney (edited 09-04-2003).]
Circuit voltage is not stated, but make sure the overload heaters are sized based on the motor-nameplate full-load current and not by lookup in Table 430-150. The table values are intended for branch-circuit and feeder sizing.
The term “motor…service disconnect switch” is mentioned, and seems to be described as possibly applied “downstream” of the individual starters. You may want to instead use fused-disconnect switches applied “upstream” as individual starter and motor disconnecting means—also sufficing as branch-circuit short-circuit and ground-fault protection.
The wiring proposed from a single 60-amp breaker to multiple starters sounds like it may be “daisy-chained,” for which the starter terminals are likely not intended in accommodating larger, possibly multiple conductors. A single disconnecting means for nine motors is not likely permitted in the case of building-ventilation motors.
Note also that local mechanical codes may additionally require individual motor-disconnecting means at each individual motor location—such as with non-fused disconnect switches.
So you would come off the 60 amp breaker with #6 to the line side lugs of the first starter then install another #6 on the lug and run to the next starter? If a fault on one of the fans occured and tripped the 60 amp breaker. the customer would lose all his ventilation. How would you troubleshoot the problem?
Well the disagrement is that I wanted to come out of the 60amp breaker to a sub-panel with 10 3 phase 15amp breakers then to the motor stater with each one having it's own circuit. He said that was to much for nothing. That's why I wanted to know if what he wants to do is legal if not I have grounds on doing it my way.
juan i like the way you are talking about doing it.
Well the disagrement is that I wanted to come out of the 60amp breaker to a sub-panel with 10 3 phase 15amp breakers then to the motor stater with each one having it's own circuit. He said that was to much for nothing. That's why I wanted to know if what he wants to do is legal if not I have grounds on doing it my way
last place i worked we had 10 exhuast and 10 intake fans about same size as you we had one central cabinet with a main dissconnect and all the motor starters and fusing inside so you could shut them all down or individualy also had a disconnect at the fan on top of the roof.