Motor starter coil voltage vs. motor voltage

[jimmyelectron]

Can someone tell me where in the NEC it says that you must use a starter that has the same coil voltage as the motor it will be starting? My salesman told me today that he could no longer get me 120 volt coil, 480 volt starters as they are a violation of the NEC. I could be mistaken, but I read it as saying that as long as the conductor insulation used for the coil is rated to 600 volts like the conductors used for the motor that you would not be in violation. He is telling me that I must use a 480 volt coil to match the 480 volt motor leads. I am using a seperate 120 volt source for the control circuit coming off a PLC.

 

[rbulsara]

Buy from his competitor.

 

[dpc]

Then your salesman is an idiot or you guys were talking about two different things. Coil voltage can be whatever you want, including the now trendy 24 V dc.

480 V control circuits are still legal, but probably not for much longer due to arc-flash issues. 120V ac control voltage is by far the most common in the US and has been for about 50 years.

Not sure what he thought he was talking about. How many beers did he have for lunch?

 

[jraef]

Wow, I thought I had heard just about every misconception known in the controls industry; but I guess not. Not only is it not true, it's ludicrous, especially because of what dpc said about the new Ar-Flash requirements making them dangerous. The word "coil" only appears once in the entirety of Article 430, the section that deals with motors and motor controls. The reference to "coil" is for trip coils in overload protection devices, nothing about contactor coils or coil voltages. The words "coil" and "voltage" do not appear in the same sentence anywhere in the NEC.

I would guess he screwed up and accidentally ordered a bunch of starters with 480V coils, now he is stuck with them because nobody uses them any more, so he is concocting a story to try and pawn them off on you!

By the way, where did you see anything that even mentioned the wire insulation rating needing to be the same?
Like rbulsara said, find another supplier.

JRaef.com
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[VxA]

Just going to echo what jraef and dpc are saying. The guy either doesn't know what he's talking about (in regards to this) or you misunderstood what he was telling you. I suspect the former.

 

[waross]

Ask the salesman to show you the rule in the NEC.
respectfully

 

[aolalde]

I never have seen that limitation in a standard. For safety reasons, low voltage is always desirable on the control circuits.

 

[jimmyelectron]

Thanks to all for the replies. I am considering switching suppliers. I found out that they did in fact overstock on pump panels for the local farming industry. The guy does such a good job of getting stuff for us that I hate to dump him. I will try to educate him before cutting him loose. jraef - I was looking at Article 725.27(B). I got the impression that 600V insulation might be required. I am going to ask him the last question dpc asked . Thanks again for the input. I wanted to make sure I wasn't missing something.

 

[dpc]

You will likely need 600V insulation for the control circuit - all the wiring generally occupies the same wiring gutter in the MCC or is in the same space in a separate starter. So if the wire is in a conduit, wireway, or panel with 480 V circuit, it has to have 600V insulation regardless of the actual circuit voltage in the cable. This is an NEC requirement.

 

[jimmyelectron]

That is what I got from it too dpc. I was going to ask the salesman the # of beers for lunch question you posted. I asked him this morning just who was telling him it was NEC and why and where from. His PA for this product line had told him it was a code violation and so they weren't going to carry the lower voltage units anymore. Come to find out the electrical inspectors in the area will let you swap coils in a downward direction, such as putting a 120 volt coil in a starter that came with a 480, but not vice versa. It sounds as though someone at the store has their wires crossed.

 

[jraef]

Engineering by Purchasing Agent. Gotta love that!

By the way, you do realize don't you that Article 725 is only referring to special installatons don't you? That is not intended for normal motor control circuits, in fact, the section you refer to is specific to Class I installations in emergency equipment which are under 30V behind a limited energy power source. I don't see the connection to motor starters.

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[Scramode]

article 300 says if the conductor are sharing the conduit or raceway the insulation class must be the same. the coil and contactor are in the same housing therfore the voltage class for the insulation must be the same

 

[rbulsara]

Coil and contactors are not conductors. Lets not read what is not there or intended.

 

[jimmyelectron]

That is a good point rbulsara, and I may have stated my initial question incorrectly. I don't think the salesman understands what he is trying to tell. He keeps crossing the conductors with the controllers. Thanks jraef for getting me back on track about 725. I would like to discuss that one more though. Would a code thread be more appropriate? Thanks again for all of the replies.

 

[jraef]

Yes a code forum would be more appropriate. Because this is an international model of forum, we don't really have a specific NEC forum, but you may get good assistance at Mike Holt's Code forum which is specific to the US NFPA-70 (the parent document that includes the NEC in case you or anyone else didn't know).

http://www.mikeholt.com/code_forum/index.php

JRaef.com
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[dpc]

Per NEC Article 300.3, any conductors occupying the same cable, conduit or enclosure must have insulation rating equal to the highest circuit voltage applied to any conductor.

In a 480 V MCC or motor starter, all field wiring must be rated for 600 V since the power circuit occupies the same enclosure.

 

[Scramode]

yes dpc is correct it is clear from the original question

 

[rbulsara]

scramode:

what dpc says is not what you are saying.

The origninal question asks if the coil has to match line voltage? The answer is no. Do the conductor insulation has to match that of the highest voltage present in a box, probably yes, but not always.

What voltage control coil would you use in a 13800kV breaker? What voltage insulation the coil condutor will have? Do not misinterprete the Code.

 

[itsmoked]

Nicely put..

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[jraef]

Not that it isn't a good idea dpc, but remember, when looking at one section of the NEC don't forget to read the beginning of that section.

300.1 Scope.
(A) All Wiring Installations. This article covers wiring
methods for all wiring installations unless modified by
other articles.
(B) Integral Parts of Equipment. The provisions of this
article are not intended to apply to the conductors that form
an integral part of equipment, such as motors, controllers,
motor control centers, or factory assembled control equipment
or listed utilization equipment.

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