motors

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lutron

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Pennsylvania
Hey Guys,

Please second guess my design.

12 fan motors (direct drive) all 460 volts 1.5 HP

1. 430.150 says 3.0 amps ,when I get my hands on the motors if 430.6 (A) (1) exception no 3 applies I shall make proper changes.

2. 430.32 (A) (3) applies, No need for heaters.

3. 430.24 OK all the motors are the same so.... 3.0 x 1.25 = 3.75 + (11 x3.0) = 36.75. I shall use #8 thhn. for my branch circuit.

4. 430.28 (1) (2) (3) yes I will adhere to these rules. I shall use 12 gauge wire and 20 amp fuses for my 12 taps to the individual disconnects. A little oversized I know, but we stock tons of #12

5. 430.53 (c) (4) I will use a 40amp breaker in the panel.

I can't say enough good about this site. I thank all that take the time to help.

P.S I am an "inhouse" Electrician so there is no bidding to deal with. However if there is a more cost effective way of doing this I'm all ears.


Thanks again
Mike
 
Re: motors

If the 20A fuses are intended to be the motor branch circuit short circuit and ground fault protection,(430.52) then the value of a non-time delay fuse should be no more than 9.0A and a time delay fuse value of 5.25A unless meeting the terms of 430.52(C)(1)exception 2 (a)or (b).
 
Re: motors

How 'bout some more info on your exact application.

Is there a controller for each motor? What serves as the controller(s) as defined by 430.81(A)? Will the fans be remotely controlled or by physically going to each location to start/stop them? Is a manually operated fused disc. an acceptable way for start/stop?

Unless these 460V. 3-phase motors have built-in running O/L protection, they will probably need protection ( usually "heaters") per 430 Part III.

Sounds like you plan to use a bkr. in panel as the feeder for these (12) motors. #8 THHN is fine for the feeder wires. If using modern components, you may find that all are listed for 75 degree C terminations. In that case you could use a 50A/3P bkr. to protect the #8 feeder wires (430.62(B) if you wish.

If this is a "plain Jane" application, then there are many standardized methods which are preferred.

For manual control it could be as simple as a fused switch at each motor with 125% fuses serving as the the branch ckt. protection, the running O/L protection, the controller, & the disc. means.

If these are remotely controlled, then you may well need starters with "heaters".

430.53 is about multiple motors on same branch ckt. I think that 430.6(A)(1) EX.3 is talking about appliances with inflated HP ratings like you find in the hardware stores.
 
Re: motors

Kiloamp 7

Thank you for taking the time to answer my post.

1. I plan on using square D combination motor starter disconnects. So I will be adding heaters.

2. My question now is do i go by the ratings on the motor 2.2Amps at 460 volts 1.5HP or do i go by 430.150 table that says 3.0Amps. I think 430.6 (A)(1)applys and i should use the nameplate for all calculations.
 
Re: motors

Generally, use the NEC table FLA of 3.0A for sizing motor branch ckt. short ckt. & gnd. fault protection. Usually 175% max. for slow blow fuses.

For running O/L protection, use the actual motor nameplate (2.2A) in this case. You'll probably see that the "heater" selection table that comes with the combo starters also tells you to use the service factor from the nameplate for heater selection.

For the most part the NEC is tailored for real world use. NEC does not require us to see motor nameplate to design electrical systems. If it did, we'd have to receive the motors before proceeding with the design. It does however, tell us to see the nameplate before buying "heaters" & proceeding with start-up.
 
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