Motor Power Circuits & Wire length 1

[elfman]

I have an application where we usually have our control panel within a short distance (<100 feet) of the motors it will be running. It is a hoist application where we have festoon cable that runs from a fixed junction box to the traversing hoist motors. From the junction box to the panel we usually try to keep the distance to a minimum. This particular installation is requiring approx. 500 feet between the junction box and panel with about 50-60 feet of festoon.

One, do I have to run the same gauge wire from control panel all the way to the hoist motors (1/2 Hp - 10 Hp, 3 phase, 60 hz.) or can I run a heavy gauge wire to the junction box to minimize losses and then run what I would normally run in the way of festoon cable for the 50-60 feet?

Two, I have NFPA 70 2011, but an unsure on specifics on sizing the wire, where do I find the best information on the hows, whats, and whys?

Any help or suggestions will be much appreicated.

 

[jraef]

1) You must do a voltage drop calculation to be sure; guesses are essentially meaningless. If you don't know how to do that, you are the wrong person to be making the decision, sorry. There are simple VD calculators available on line, but nothing replaces the human element of factoring in myriad other variables and unknowns. In other words with no practical experience, you will not know what you don't know.

2) All information for sizing the motor power conductors is in Article 430, which essentially trumps other sections.

"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
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[dpc]

1. Yes, as long as the smallest wire used meets minimum size required.

2. Not sure where this is being installed, or the exact code jurisdiction, but a safe sizing criteria is the National Electrical Code if being installed in the US. See Article 430. Basically the conductors must have a capacity at least equal to 125% of the motor full load amps as given in the tables in Article 430, unless your actual motor amps are HIGHER than what it is in the tables.



David Castor

http://www.cvoes.com

 

[elfman]

jreaf: Thanks but no thanks.

dpc: Thanks. Your's was helpful.

 

[dpc]

Well, voltage drop can be a concern. I agree with everything jraef said.



David Castor

http://www.cvoes.com

 

[waross]

I agree with jraef and dpc. Further comment reserved.

Bill
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