ECN Forum Forums General Topics of the Trade General Discussion Area Multiple Motors

I am installing 6 identicle pieces of equipment in particular area. Each unit has a 1hp. 460 volt 3phase motor, FLA is 3amps. I have motor starters complete with OL relays set at 3.75 amps on each unit. I am planning on having 1 branch circuit to supply all six units and have a twistlock plug and receptacle at each unit for disconnecting means. According to my calculations a 20 amp circuit would be right, 3amp X 5 units = 15 amps + 3.75 amps for the 6th unit = 18.75 amps (or 20 amps). Am I figuring this right? Also I currently have a 30 amp unused branch circuit at this location. Is there a problem with using that circuit and installing 20amp fuses on each phase before continuing on to my recepts? I know this setup will work, but does anyone know of a safer and/or more practicle way of connecting this equipment?

Nevin, check out your math here

http://necdirect.org/cgi-bin/SoftCa....htm?L+necnonmembers+rwfl8151+1000047299


[This message has been edited by sparky (edited 09-09-2001).]

I might be sticking my foot in it here, but if I am, we'll all benefit from it.

I don't feel that this installation would comply with 430-53. Part (a) would require the branch circuit to be protected at not over 15 amps.

Part (b) the smallest rated motor is not protected per 430-52 & table 430-152. 300% x 3 amps = 9 amps which would require 15 amp fuses (see standard sizes 240-6).

You might be able to comply with part (c) or (d), but it would depend on what you're using as a controller.

If all motors don't run at the same time, going to 15 amp fuses looks about right. Otherwise, this installation would have to come into compliance with 430-53(b) or (c) or (d).

Tom

[This message has been edited by Tom (edited 09-09-2001).]

So it looks like i have 2 options, 1. to comply with 430-53(a) my branch circuit has to protected with an OCPD of not more then 15 amps. or 2. comply with 430-53(c) having motor controllers with proper listings for group installations etc which would allow me to use a 20 amp circuit (3amps X 6 units = 18amps) next normal size above that = 20 amp circuit.

I don't know how much luck you would have with the "marking" part, but the rest of it comes down to a combination starter (built in breaker or switch with fuses). Otherwise, your choices are as you stated them.

Good luck.

Tom

Actually, you have one more choice, but I don't think it changes much. You could call the 20 amp circuit a "feeder", or even leave it as a 30 amp circuit, but you would still need combinations starters with a breaker or set of fuses in them. See part E of article 430.