OT: Motor connection methods

Milt · Jun 17, 2006

I work in a paper converting plant. Our equipment uses a lot of different electric motors ranging in size from fractional to 150hp. I have been tasked with creating a standard for the electrical connection of these motors, primarily US made, with a few european made scattered about. I can find no reference material about wiring methods such as wire nuts, bolted togehter lugs, etc, and reasons to prefer one over another. Can anyone provide references I can research?

RefineryGuy · Jun 17, 2006

We use a lot of Burndy Insulated Multiple Connectors. If you do a search for Burndy, you'll see their website. We've had pretty good luck with them. Anything 100HP and Larger we still use bolt on lugs.

Leadfoot · Jun 17, 2006

Being in the drive service business, I get to see many methods of connections in motor junction boxes and j-boxes in general.

The methods used are too many to even try to remember. I have found different electrical contractors use the standard of their company. I have asked them why they used their method and would get answers ranging from company standard, local code, NEC requirement to "I like this one".

Additionally, larger horse power and voltage connections have different requirements than 5hp and less.

I personnally do not like wire nuts. I use them on my shop test motors to allow easy changes from 230 to 480 for testing a drive. In any permanent installation, I perfer lugs and bolts with the appropriate tape up.

TConnolly · Jun 17, 2006

We just started using these for smaller motors. Very very convenient.

http://www.wago.us/83.htm?L1=/produ.../products/141.htm&HL3=150&B=/products/901.htm

elevmike · Jun 18, 2006

Milt, This is the type of question that's usually answered with another question. A lot depends on a lot. Motor HP voltage, type of leads etc..

Just remember to use LOTs of rubber tape and stay away from spring loaded clips or wire nuts.

cntrlfrk · Jun 19, 2006

We've always ring lugged/ bolted leads together on all size motors. Recently we began using a gel-type goo tube that slides over the terminals that is re-usable. It's safe, and quicker than cutting through a bunch of tape and re-taping.

John Hawkins · Jun 19, 2006

Any 3 phase motor over 5 HP, here at the plant, is connected with split bolts. These are then taped with varnished cambric tape then taped with linerless rubber tape, then with #88 tape. The reason for cambric tape is to be able to take the connection apart. After the rubbet tape sinks into the threads of the split bolts you will spend all day to get the connection apart. Tried & True --John H

russrmartin · Jun 19, 2006

I would agree with John Hawkins. If you are going to use wire nuts, you should know what their maximum ratings are. I have never seen anything but wire nuts used on motors less than 5 HP, and I've never seen it cause a problem. Most 5HP motors I've seen were wired at 480, and FLA are right around 8 amps. This won't test wire nuts much at all, assuming a good connection is made. Motors greater than 5HP, we also lug together with a split bolt, then tape with rubber tape, glass tape, and finally regular electrical tape.

Sliver · Jun 19, 2006

Like John and Russ we used to use the cambric, linerless rubber, and super '33'...over split bolts for all larger motors.
Then we were introduced to 'self vulcanizing' tape.
No need to use cambric. Just a finishing layer or two of super '33'. When it comes time to remove as you cut into it it peels itself right off.

Brian.

tomalbright · Jun 19, 2006

If you use the cambric, wrap it sticky side out!

Wire nuts on 5 hp and below sounds good. I am a fan of split bolts. The simpler you keep the connection, the more reliable it will be and easier to maintaint.

Occasionally we have motors that are pre-lugged. On these a nut & bolt and a wrap are usually done.

Wow, that's 3 things. I could probably name them all day...

As far as a standard for all types, I think you will have to make a decision that the bean counters and the maintenance guys will all agree on.

jraef · Jun 19, 2006

Wire nuts are a bad idea regardless of motor size IMHO. They are not designed with vibration in mind, they were designed to make connections in splice boxes and outlets. Vibration causes the metal threads to burrow into the softer copper, which eases the pressure and risks a loose joint, which heats up and boom! No more motor circuit. I have seen it too many times.

Scotchlocks (soft wire nuts with springy threads) are even worse. I've even seen cheap wire nuts that are all plastic. All in all, not worth the risk to save a few cents. Split bolt or crimp on ring terminals with screws and lock washers, covered with cambric to facilitate future reuse, covered with rubber tape in case it vibrates against the pecker-head wall, covered with 33+ or = to protect the rubber and keep it from unraveling. Tried and true, don't mess with what works.

Bigger motors almost always come with connection blocks or studs. If not, find a better motor supplier!

plchacker · Jun 19, 2006

One of the worst situations I have walked into was a mill where wirenuts were used on most every connection below 50HP. It took almost a year to start good habits, and correct most of the electrical troubles in that particular mill. Wirenuts on motors was the first sign of trouble.

I agree with most everyone else, splitbolts and tape. Motors should have a long life, and the connections should last as well. If you find yourself replacing a lot of motors, there is a reason. The newer products are worth a look.

Cambirc wrapped inside out always worked well for me. Followed by 3M 130C and either 33 or 88. I like 88 better, but 33 works. These were all 480VAC motors. 5 HP up to 300 HP.

Milt · Jun 20, 2006

Thank you

Thank you all for the suggestions. I will write up two standards using either split bolts or bolted together lugs and submit them for approval.

OT: Motor connection methods

Milt

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RefineryGuy

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Leadfoot

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TConnolly

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elevmike

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cntrlfrk

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John Hawkins

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russrmartin

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Sliver

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tomalbright

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jraef

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plchacker

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Milt

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