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Multiple Motors #4043 09/07/01 10:19 PM
Joined: May 2001
Posts: 30
N
Nevin Offline OP
Member
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?

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Re: Multiple Motors #4044 09/09/01 06:04 AM
Joined: Oct 2000
Posts: 5,389
S
sparky Offline
Member
Nevin, check out your math here [Linked Image]

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


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

Re: Multiple Motors #4045 09/09/01 12:03 PM
Joined: Jan 2001
Posts: 1,044
Tom Offline
Member
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).]


Few things are harder to put up with than the annoyance of a good example.
Re: Multiple Motors #4046 09/09/01 08:42 PM
Joined: May 2001
Posts: 30
N
Nevin Offline OP
Member
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.

Re: Multiple Motors #4047 09/11/01 05:05 PM
Joined: Jan 2001
Posts: 1,044
Tom Offline
Member
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


Few things are harder to put up with than the annoyance of a good example.
Re: Multiple Motors #4048 09/12/01 05:57 PM
Joined: Jan 2001
Posts: 1,044
Tom Offline
Member
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.


Few things are harder to put up with than the annoyance of a good example.

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