Field and armature wiring in same conduit?

[AutoXer]

Here's the situation:

An upgrade on our equipment requires a new DC motor. The only available spare embeded conduit is 2 x 1". A 1" is big enough for the field leads(10AWG), but isn't big enough for the armature leads(2/0AWG). However we could split up the field and armature leads and put one of each in the 2 1" conduits. This would be a no-no with three-phase power due to inductive heating, but can you do it with DC motors?

 

[itsmoked]

How close are these two conduits? Nearly touching close?

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[AutoXer]

I'd estimate 1/4 to 1/2 inch. I'd estimate the run at about 150 feet.

 

[itsmoked]

Then off hand I can't see much of a problem. There may be control issues someone will chip in with but the closeness of the two conduits will limit the massive B-Feild that will be created in the gap between the conduits.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[Skogsgurra]

There is a considerable 300 Hz (Europe) or 360 Hz (US etc) AC component in the armature current. If you are running 6-pulse thyristor rectifiers. Sometimes as high as 30 % of motor rated current. Its heating effect is actually more than a 100 % 50 or 60 Hz current. So, for same reasons that you shouldn't do it with an AC system, you should be careful here, too.

Eddy current heating is proportional to frequency squared, so your 30 % ripple at six times mains frequency will heat^.3*6^2 = 10.8 times the rated 50/60 Hz current. Even with as little ripple as 10 %, you get 3.6 times more heating.

The problem does not exist with WL sets. But I don't think youv'e got one of them. Have you?

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[waross]

Another possible issue is wire damage, mixing #10 AWG with 2/0 AWG in a 150 foot run may be hard on the #10s if the insulation isn't robust. Can you use something like 2 x #2 AWG and a #10 AWG in each pipe, or 2 x #2s in each pipe and both #10s in one pipe with one set of #2s?
Phisically and code wise it depends on which type of wire you choose to use.
respectfully