Multiple motors and control circuits - can they be combined

[whiggins]

Here's the situation. I've got a building (industrial establishment) where the motors in the building are to be fed from another MCC building 300 or so feet away. The motor loads in question are for hot water unit heaters. The motors are 480V with a local control station and all around 1/2 HP.

I've got 8 of these motors and their associated three wire control circuits. They're also located in a Class 1 Div 2 location, thus the remote MCC. If I'm reading 725.48 (B) (1) (2008) correctly I would be required to have 8 separate conduits, one for each motor and the associated controls. Am I missing something here? Is there a way to combine some of these and avoid so much conduit?

 

[dicklaxt]

I don't know if there is a requirement one way or the other.I started out as a rookie and an old guy told me to route them seperately and I did so for the next several thousand motors over the years.Think about it this way ,if you have all your eggs in one basket and one breaks they might all break before all is said and done. When doing a cable tray distribution many are routed in the same tray,,,,,,,,,,kinda makes you wonder doesn't it.

dick

 

[masterinbama]

I pull multiple motor circuits in the same conduit all the time. Just be sure to apply all of the required derating.

 

[kwired]

Here is section OP questioned:

(1) In a Cable, Enclosure, or Raceway. Class 1 circuits and power-supply circuits shall be permitted to occupy the same cable, enclosure, or raceway only where the equipment powered is functionally associated.

I've got 8 of these motors and their associated three wire control circuits.

Sounds like the controls are associated to the power conductors to me, just make sure you have class 1 control circuits, class 2 control circuits are not allowed in same raceway with power conductors at all.

I'm not as likely to do this with 8 motors, but is not prohibited either. A single motor and an associated control circuit in a long run - yes, I do that all the time, saves running a second raceway. With 8 motors the chance of multiple raceways or larger conductors goes up - so it really depends on some of the specifics. If they are all small enough motors that the conductors can be relatively small even after deration, I may still run everything in one raceway.

 

[whiggins]

The reason for my question is the "functionally associated" part of the code. For example, consider two motor feeders in one conduit with their associated 120V control conductors; lets call them motor A and motor B. The control conductors for motor A are obviously functionally associated with motor A, and the control conductors for motor B are obviously functionally associated with motor B. If all the conductors (motor feeders and control) are in the same conduct; however, motor B control conductors are not functionally associated with motor A and the motor A control conductors are not functionally associated with motor B.

So, does the "functionally associated" mean that as long as the control conductors are "functionally associated" with at least one motor this is an okay installation?

 

[G._S._Ohm]

The reason for my question is the "functionally associated" part of the code. For example, consider two motor feeders in one conduit with their associated 120V control conductors; lets call them motor A and motor B. The control conductors for motor A are obviously functionally associated with motor A, and the control conductors for motor B are obviously functionally associated with motor B. If all the conductors (motor feeders and control) are in the same conduct; however, motor B control conductors are not functionally associated with motor A and the motor A control conductors are not functionally associated with motor B.

So, does the "functionally associated" mean that as long as the control conductors are "functionally associated" with at least one motor this is an okay installation?

My interpretation
If the motor control lines and motor feeders are functionally associated in that they share a motor
then
lines & feeders in one conduit, f a

If the control lines are f a because they all do control
then
control lines in one conduit, f a

If the feeders are f a because they all supply power
then
feeders in one conduit, f a

The function of a motor is to supply hp, so the feeders are more strongly f a than the controls for these motors.

The NFPA should offer courses in linguistics. Maybe they do.

 

[G._S._Ohm]

OK, using Verdana regular 14

c = control
f = feeders


unassociated
c1 in it's own conduit
c2 "
f1 "
f2 "


all 2x2 combos
f1 c1 in it's own conduit
f1 c2"
f2 c1"
f2 c2"
c1 c2"
f1 f2"


assoc. 2x2 combos
f1 c1"
f2 c2"
c1 c2"
f1 f2"


f + c in conduit assoc. with hp, strength = 2
f + f in conduit assoc. with hp, strength = 3
c + c in conduit, assoc. with hp, strength = 1

 

[petersonra]

IMO it is OK to run the control conductors with the associated motor conductors but you can't run the control conductors for one motor with the power conductors for another motor, so as a practical matter you have to run them seperately grouped by motor.

Having said that is there any real benefit to calling the control conductors Class 1 conductors rather than just making them larger and running them as normal conductors. then you can do whatever you want.

 

[whiggins]

Having said that is there any real benefit to calling the control conductors Class 1 conductors rather than just making them larger and running them as normal conductors. then you can do whatever you want.

Can you do that? I didn't think Article 725 gives you the choice.

 

[kwired]

IMO it is OK to run the control conductors with the associated motor conductors but you can't run the control conductors for one motor with the power conductors for another motor, so as a practical matter you have to run them seperately grouped by motor.

Having said that is there any real benefit to calling the control conductors Class 1 conductors rather than just making them larger and running them as normal conductors. then you can do whatever you want.

If you use 14AWG control conductors with a 15 amp overcurrent device, I suppose you could to some extent do this, but that means your control conductors are to be considered current carrying conductors as well as the power conductors. So you could end up increasing conductor sizes of all conductors in the raceway even though the control circuit only draws 1/2 amp and in reality does not add any significant heating to the raceway.

---------------

Is control circuits to more than one motor considered functionally associated? I don't know. I always figured if part of the same process, all motors and controls are functionally associated. Now if you have process related conductors and general lighting conductors sharing the same raceway, that may not be considered functionally associated, or maybe it is if the lighting is for the process area only.