Motor Lead Wire 2

[flandrax]

I was wondering if there was a limitation to how long leads could be on a motor?
Can they be run in conduit?
Are there any standards for this?

Thanks in advance,

 

[waross]

There are lots of answers to such a broad question. What, specifically, do you have in mind?


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[electricpete]

Not knowing the background of the original poster, I make an obvious comment: The standard practice is that lead wire goes into the attached term box and not beyond into the power system conduits.

You would surely want to think carefully about doing anything different. Typically different types of wires are used in each application. Finely stranded for motor lead wire... often with minimal mechanical armour, absolutely no shielding for lead wire (medium voltage). Also what benefit could there be to terminating anywhere other than motor term box? What happens when you swap the motor?


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[electricpete]

Also I am guessing NEC wouldn't allow motor lead wire running past motor term box, but I can't quote any paragraph number.

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[flandrax]

I have seen and repaired motors with leads up to 15 feet. The motors where designed that way. I have a customer wants to make the leads on his motor 30 feet.
I was wanting to know if the NEC does govern this?
What kind of problems exist?
Will i have to up size the wire?
So on.

 

[hesselberth]

Baldor/Reliance Dry Kiln Duty Motors come standard with 8 foot leads. never seen anything longer though.

 

[waross]

Baldor/Reliance Dry Kiln Duty Motors come standard with 8 foot leads. never seen anything longer though.

I wish these had been available when I was designing lumber kiln control packages.
This sounds like a kiln application.
Submersible pumps use very long motor leads.


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[rhatcher]

Normally, the motor lead wire is only long enough to reach the terminal box and to allow connection to the line leads. I am not sure why anyone would want them to be longer than that and I have never seen a motor where the terminal box was on a stand pipe that was 30 feet from the motor. You should ask your customer what his reason is.

Otherwise, I do not know of any restriction that prohibits the motor leads from passing through the terminal box, into the conduit, and on to another connection point 30 feet away. Of course, it would be a real pain to pull the leads through the conduit each time you changed the motor.

 

[electricpete]

One reservation I can think of is whether the lead wire meets UL specs for running in conduits. I don't know for sure, but I suspect the answer would come from studying tables 1-3 on pages 10-12 of 57 below:

http://www-group.slac.stanford.edu/essg/pdf/mgwire.pdf

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[electricpete]

meets UL specs

What I meant was... is it UL listed for the purpose called out by the NEC.

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[waross]

Hi rhatcher;
Time was when lumber kilns had propeller fans mounted directly on the motor shafts. Ambient temperatures during operation could exceed 100 deg C. The motors were specially built for kiln duty. Connections to the motors was always a problem. Many installations used mineral insulated cable to feed the motors.
Long motor leads would allow the motor connections to be made outside the kiln where normal wiring methods could be used.
Many kilns now have the motors mounted outside the kiln and use belts or a drive shaft to drive the fans.
Back in the day of inside the kiln mounted motors, I would have liked 30 Ft. long motor leads.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[rhatcher]

Good answer waross. We do work on vent fans where the motor is mounted inside a duct and the leads extend through a pipe to a junction box on the outside. Of course, these are for marine duty and seldom have ducts more than 6 or 8 ft in diameter. But, having read your post, I have no problem imagining larger ducts (or other things) that require longer leads. Of course, thirty feet leads suggest a diameter of 60 feet! Still, good answer.

electricpete, I do not see anything in those tables regarding conduit. Perhaps you can enlighten me. If there is a reference to conduit then I guess I'll need to check the markings on our lead wire to see if it meets the specifications in your reference and, if not, I'll need to retract the statement that there may be no problem with pulling lead wire through a conduit.

Otherwise, I think waross has nailed the answer. Of course, if the OP isn't sure about the reason or the correctness of doing so, all he needs to do is ask the customer for clarification of his request per my suggestion.

 

[electricpete]

I am not in a position to enlighten you about the maze of UL and NEC requirements. My understanding is that cables have a UL designation which corresdonds to specific NEC requirements. The NEC requirements do not extend to motor T-leads, so I would be surprised if T leads had a UL rating that satisfied NEC requirements. Maybe the NEC question would be better posted in the power engineering or code forum.

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[electricpete]

Another issue would be ampacity of the cable. NEC requires something like 125% FLA rating using NEC methods for determining ampacity which I think are pretty conservative. It may not be a deal-breaker, but it is something that would have to be looked at.

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[waross]

Hi rhatcher. Imagine a shed with a gable roof. There is a ceiling called a fan deck, with a slot near two opposing walls. The shed is filled with lumber with spacers between each course of lumber. The air circulates through the slots, up through the slot in the fan deck, through the heating coils and fans and down through the other side and back through the lumber stack.
One common design had the fans on ten foot centers in a line down the center of the attic space above the fan deck.
8' leads would allow connections to be made above the roof outside the kiln. Good.
15' leads would allow the connections to be made at ceiling ("fan deck" in dry kiln terminology) level outside the kiln. Better.
30' leads would allow connections (and trouble shooting) to be done at ground level outside the kiln. Best.


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[rhatcher]

Waross, thanks for the more detailed explanation. I have worked around wood kilns once or twice in the past but never on the fans that you describe. After hearing you talk I guess that I was lucky.

For electricpete, I wasn't asking you to enlighten me on the whole of UL or the NEC. I was simply asking for you to point out the part in the tables of the reference that applied to conduit or to motor lead wire. I could not find anything there and thought that I was missing something.

By the way, the lead wire we use for low voltage motors is EPDM, 600V, 150C, UL3340/3374. In either case, I agree that before anyone starts pulling motor lead wire, or any other type of wire, into a conduit that they should be certain that it meets all applicable local codes for the type of installation they are doing.

 

[electricpete]

I am not in a position to enlighten you about the maze of UL and NEC requirements.

Ray - I can guarantee my answer was not intended the way that it sounded. But in retrospect it sounds bad so I need to explain... I didn't use the word "enlighten" to suggest I have a whole mess of knowledge on the NEC... I just used that word because you used the word ("enlighten me"). And the comment "I am not in a position" was supposed to mean that I don't know.... I don't know enough about NEC requirements for cable to figure out what UL numbers are required (hence my suggestion to post in the other forums). And I don't see a direct answer to these questions in the link I posted either.

One thing I do know is that NEC does not apply to the motor lead function. So, it is certainly possible and plausible that motor lead wires do not meet the specific UL listing requirements associated with the various NEC paragraphs. We are in agreement that it needs to be verified.

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[electricpete]

I did talk to an engineer more familiar with me with NEC. He pointed me to NEC 310.13

Conductor Constructions
Insulated conductors shall comply with the applicable provisions of one or more of the following: Tables 310.13, 310.61, 310.62, 310.63, and 310.64.

Table 310.64 applies to 600vac and below. It lists cable type using terminology similar to the first column of the link above... doesnt’ really help. But I listed it here for historical reference.

A more relevant link is here:

http://www.ul.com/global/eng/docume...able/appliancewiringmaterial/stylenumbers.pdf

How Style Numbers are determined
UL categorizes AWB into 5 sections, numbered 1 to 5.

3000 – 3009 – Section 3 - Single Conductor, Thermal setting, insulated wire.

I think your 3340 and 3347 are “style numbers” for AWM.

So what does AWM mean?

http://www.ul.com/global/eng/pages/offerings/industries/wireandcable/appliancewiringmaterial/

Appliance wiring material
Unlike most wire categories, appliance wiring material (AWM) is a recognized component. This means that AWM is used in UL Listed or Classified end products. AWM wires are intended as factory-installed or factory-provided components of complete equipment submitted for investigation, rather than for direct separate installation in the field. The final acceptance of the component depends on its installation and use in or with complete equipment submitted to UL.

Example:

http://www.wcwc.com/053818/specsheets/pdf/epdm.pdf

EPDM/3340/3374/CSA CL1503/AWM
Can be used as appliance wire and as lead wire for motors, appliances, transformers, coils, ballasts or solenoids where high temperature is required.[There is no mention of using it for any other application]

So from my bit of research using google I am inclined to think UL 3340 / 3374 is a niche cable intended for use as part of appliances, but not specifically intended for field use.

I am under the impression that cables have a very wide degree of differentiation/specialization (look in a cable catalogue or website for bewildering variety). We choose the cable designed for the purpose we have in mind. What exactly would not work about this lead cable I don’t know other than the compliance aspect. We already talked about ampacity... that depends on how the cable is installed. Also NEC has requirements related to damp locations, wet locations. Sometimes there are other requirements on the fire resistance or smoke resistance of cable (I’m not sure if I have those terms right). And more that I am not in the least familiar with.

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[electricpete]

Correction in bold: "Table 310.13 applies to 600vac and below."

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[electricpete]

Another correction: "UL categorizes AWM into 5 sections, numbered 1 to 5."

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