Multiple Conductors in Multiple Conduits

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chiplein

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I have a 300hp VFD going to a 260hp motor. The VFD is about 80' away from the motor. I'd like to run a separate conduit for each phase and the ground of the motor for a total of 4 conductors and conduits. Is this legal or do I need a ground conductor for each conduit?
 
Re: Multiple Conductors in Multiple Conduits

chiplein Not only do you need a ground in each conduit if you run any, you need each phase in each conduit. A,B,C,G in each raceway.
 
Re: Multiple Conductors in Multiple Conduits

Bob - so I couldn't just run 1 500kcmil conductor w/ 1 ground conductor in 3 conduits and be legal?

phase1 = 1 conduit, 1 phase conductor, 1 ground
phase2 = 1 conduit, 1 phase conductor, 1 ground
phase3 = 1 conduit, 1 phase conductor, 1 ground
 
Re: Multiple Conductors in Multiple Conduits

No you can not, the NEC will not allow it.

300.3 Conductors.

(B) Conductors of the Same Circuit.
All conductors of the same circuit and, where used, the grounded conductor and all equipment grounding conductors and bonding conductors shall be contained within the same raceway, auxiliary gutter, cable tray, cablebus assembly, trench, cable, or cord, unless otherwise permitted in accordance with 300.3(B)(1) through (4).

(1) Paralleled Installations.
Conductors shall be permitted to be run in parallel in accordance with the provisions of 310.4. The requirement to run all circuit conductors within the same raceway, auxiliary gutter, cable tray, trench, cable, or cord shall apply separately to each portion of the paralleled installation, and the equipment grounding conductors shall comply with the provisions of 250.122. Parallel runs in cable tray shall comply with the provisions of 392.8(D).

Exception: Conductors installed in nonmetallic raceways run underground shall be permitted to be arranged as isolated phase installations. The raceways shall be installed in close proximity, and the conductors shall comply with the provisions of 300.20(B).
Click to expand...
 
Re: Multiple Conductors in Multiple Conduits

Run all phases together. To measure amps, you place the clamp-on around one wire, not all three in a 3 phase circuit. If you go around all three, you don't get a reading as the field cancels. You do not want induction and heating between the conduits.
 
Re: Multiple Conductors in Multiple Conduits

I would be getting in over my head (meaning I can't) trying to explain why this can not be done, short answer is the conduits will get hot, real hot with I am guessing about 300 to 350 amps of load.

You mentioned 500kcmil, run one 3.5" or 4" conduit and install them all in this, or split the load into parallel 2/0 or 3/0s run in two 2" conduits.(A,B,C,G in each)

In either case you will need some cable pulling equipment.

[ November 06, 2003, 07:40 PM: Message edited by: iwire ]
 
Re: Multiple Conductors in Multiple Conduits

IWIRE is correct. You only have two feasible options.

1. Run one 4 inch with 3-500 MCM phase conductors (A,B,C) plus EGC.

2. Run two 2 inch conduits with 3-3/0 phase conductors (A,B,C) plus EGC in each of the two conduits.

[ November 06, 2003, 08:05 PM: Message edited by: dereckbc ]
 
Re: Multiple Conductors in Multiple Conduits

Chiplein: Just to be safe, suggest you check the minimum wire size with the supplier, especially if it will be operated at lower speeds and 80' from the motor.
 
Re: Multiple Conductors in Multiple Conduits

Also check with the manufacturer on the distance limits the VFD can be placed from the motor and that the motor itself is compatible with the VFD.
 
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