How to protect against electrical arcing in motor electrical connection box

I have had a problem a couple of times with my current set-up. I am running a 15HP motor for my phase converter and the box where all the connections are made is quite small to cram all the wires in and I have had a problem with arcing.

I have the 6 AWG wires plus the 10 AWG wires connected together with ring terminals and a bolt and a nut and then I wrap the heck out of it with electrical tape and cram everything back in there. Twice in the last two or three years I have had a problem with the heat eventually melting the tape and causing a short.

I have never felt really good about this but what is the better way to insulate the connectors? Can I use potting epoxy on them?

I just ran all new wires (which is a real pain to snake through) and I want to solve this once and for all.

Thanks - Joe

Use a better/more-appropriate tape, if you can get ahold of any. For situations like yours, I bolt the connections, wrap them with glass tape, and then overwrap them with a long-life high-temp elastic tape. I'm not in my shop right now, so I can't give you the 3M numbers for the tapes, but they are standard product.

There is a definite difference between cheap "electrical tape" and quality tape. Not so much in the vinyl of the tape itself, but in the adhesive systems. Quality tape won't creep for years (decades) even in a warm environment.

If you have lost faith with adhesive vinyl electrical tapes altogether, use one of the silicone self-fusing electrical tapes. No adhesive to let loose! I'd still recommend glass tape as the first layer, under the silicone self-fusing tape.

Joe Miranda said:

I have had a problem a couple of times with my current set-up. I am running a 15HP motor for my phase converter and the box where all the connections are made is quite small to cram all the wires in and I have had a problem with arcing.

I have the 6 AWG wires plus the 10 AWG wires connected together with ring terminals and a bolt and a nut and then I wrap the heck out of it with electrical tape and cram everything back in there. Twice in the last two or three years I have had a problem with the heat eventually melting the tape and causing a short.

I have never felt really good about this but what is the better way to insulate the connectors? Can I use potting epoxy on them?

I just ran all new wires (which is a real pain to snake through) and I want to solve this once and for all.

Thanks - Joe

Click to expand...

All electrical boxes have a maximum number and size for the conductors. You need more space, will a standard extension box fit? If not you get to make something, cut most of the back out of a 4" square box, de burr the edges, bolt it on. You need air space around the connections. Are the connections good for sure? Bad connections create heat. What sort of tape are you using? Use 3M scotch super #88 tape, the taiwan crap from the big box is not the same.

Thanks for the suggestions guys. I always use 3M electrical tape but I never new there were other options. I just found 3M 69 glass filled cloth tape.

I just found and ordered this: 3M™ Glass Cloth Electrical Tape 69 is a white glass cloth tape with a high-temperature thermosetting silicone pressure-sensitive adhesive. It is designed for use
in 600-volt dry location applications motors, and transformers with and without varnish
coating. Key attributes like high mechanical strength and resistance to high
temperatures provide excellent performance. The thermosetting adhesive provides an
increased bond once applied in areas of high ambient temperatures. The
thermosetting adhesive provides elevated temperature performance up to Class N
392°F (200° C) temperature rating.

I like it - $25 with shipping - if all my problems were this simple!

John - I will use a bigger box as well - yeah space and air = good!

Thanks guys!

moonlight machine said:

All electrical boxes have a maximum number and size for the conductors. You need more space, will a standard extension box fit? If not you get to make something, cut most of the back out of a 4" square box, de burr the edges, bolt it on. You need air space around the connections. Are the connections good for sure? Bad connections create heat. What sort of tape are you using? Use 3M scotch super #88 tape, the taiwan crap from the big box is not the same.

Click to expand...

Listen to Moonlight. Bigger box, Better tape.

CarlBoyd

I think that if you look at the old methods friction tape was specified for the bolted connections. Our plant was built in the 20s, and friction gape was very common. It is more puncture resistant than vinyl.

Joe Miranda said:

Thanks for the suggestions guys. I always use 3M electrical tape but I never new there were other options. I just found 3M 69 glass filled cloth tape.

I just found and ordered this: 3M™ Glass Cloth Electrical Tape 69 is a white glass cloth tape with a high-temperature thermosetting silicone pressure-sensitive adhesive. It is designed for use
in 600-volt dry location applications motors, and transformers with and without varnish
coating. Key attributes like high mechanical strength and resistance to high
temperatures provide excellent performance. The thermosetting adhesive provides an
increased bond once applied in areas of high ambient temperatures. The
thermosetting adhesive provides elevated temperature performance up to Class N
392°F (200° C) temperature rating.

I like it - $25 with shipping - if all my problems were this simple!

John - I will use a bigger box as well - yeah space and air = good!

Thanks guys!

Click to expand...

Yes, use this with #88 over it. When I was an electrician, 1974-1979 I connected 100's of motors, little 25 hp's to 500 hp. We used cable clamps, carny's the guys called them to connect the wires and then wrapped the connection with a real thick and soft tape and then #88. I'll never forget the Minnesota winter of 1978-79 working outside all winter wiring a giant gravel crushing machine, shaker and all the conveyors. you kept the tape in your under shorts or it would not flex or stick. Made me wonder if being an electrician was such a good idea.

Terminating, MotorTerminal Connections

+1 for the friction tape. It's tough enough for high vibration and builds thickness quickly and is the least expensive. I also like that it's not sticky enough to be a pain the next time it needs to be undone. Tapes that fuse together under heat are a real pain the next go round.

My preferred method is a good 1st layer of 33+ tape for the 600V insulation rating. Then a medium layer of friction tape for some bulk, to shield against connections rubbing through from heat, vibration, and plastic creep under physical and thermal stresses. Then a final outer-wrap of 33+ to bind the friction tape and provide a moisture barrier.

I would also tell you that "training" the wires into the box, no matter how tight the fill is, is more important than the tape you use.

Joe Miranda "I wrap the heck out of it with electrical tape and cram everything back in there."

Click to expand...

The cramming part is why your having problems. Train the wiring in a circular form, around the enclosure before you start terminating or bolting the connections together. Wind all of the conductors in the same direction of rotation as far against the back of the enclosure as possible. The idea is to make a helical spring with the conductors. Then pull them back out, just enough to make the connections. Then you won't need to cram them back in, they will want to easily go back into the spring shape that they were formed in, in the rear of the enclosure. In this fashion you will have much less force of the connections crammed in and vibrating against the enclosure walls and cover.

I like to put the smaller motor lead splice connections in the rear of the enclosure first. Then install the heavier supply conductors on the top of the assembly for easier access of the larger conductors. On the coils, bend the terminations to the center of the space to avoid them rubbing on the enclosure walls or cover in their final resting position.

SAF Ω

There is one catch to using friction tape. The way it was intended was to first wrap the joint with rubber tape for electrical insulation and then friction tape for mechanical durability. You wind up with a splice as big as your hand.

Tom

I've always been fond of using business cards to assure that exposed connections won't come together. Paper is a pretty good insulator, and the business cards of insurance agents and hearing aid sales people seem to be available in all most any location.

wrap the mechanical connection, then cram a card between the hot spots ;-)

CalG said:

I've always been fond of using business cards to assure that exposed connections won't come together. Paper is a pretty good insulator, and the business cards of insurance agents and hearing aid sales people seem to be available in all most any location.

wrap the mechanical connection, then cram a card between the hot spots ;-)

Click to expand...

Yeah, we used to use card board from boxes in raceways and sutch. 60 cycle vibration will eat through tape on your connections, when your 480v panel feed goes to ground you get some pretty spectacular results.

Well covered thread...I have always wrapped motor connection first with Scotch (varnished) cambric tape, then with Scotch 88 tape. Maybe this was pointed out above but cambric tape isn't the white stuff and cambric is used for its super high dielectric strength plus it super abrasion resistance.

Stuart

Purchase some heat shrink tubing; ebay has an amazing selection, mostly from China. You'll want 1mm pre-shrink thickness, and perhaps color coding.

I've given up on electrical tape where heat or petroleum-based fluids are involved. Practically speaking, it's useless for patching cuts on extension cords.

Some heat shrink vendors describe the width of the flat tubing, others describe the diameter when tubular. Pay attention to this, and the thickness.

And there are these, also found on ebay, as "insulated taps" or "terminal blocks".


Try this search: (tap, terminal, block) insulated (polaris, ilsco, burndy) | eBay

Electrical boxes in general have a minimum volume per wire required. That's boxes used in wiring a facility.

MOTOR wiring boxes are an egregious exception to this. They have no such requirement, and are nearly always designed just on the edge of being too small to physically do the wiring.

Yes, absolutely, "training" the wire before putting it in is often just about essential. Same with planning each connection so the wires lay parallel and do not have to cross under or over others. Any crossing takes up extra room, and can also put forces on the wires that lead to cutting insulation. The wires ideally should lay together without force, and the separate bundles should lay together overlapping as little as possible, but again laying with wires parallel.

Bulky, irregular connections, like terminals bolted together, have sharp edges and make things worse in general. Taping them with padding to minimize cutting makes them bulkier. Avoid if possible. Many do not like wire nuts. But they are approved connectors, if used per instructions for approved wire combinations, and they are both insulated and fairly small. Wrapping them with tape can help avoid any wires touching.

Insulated lugs like the polaris connectors or the ilsco's.

Or for tape. Two half lapped layers of Scotch 130C with 1 half lapped layer of Scotch 69 glass tape over it.

Or 3M low voltage motor termination kits

http://solutions.3m.com/wps/portal/...ts-1-kV-and-less-?N=5429244+3294176902&rt=rud

or run them in parallel one coming in one side and going out the other and trim your hardware, and use Raychem heatshrink. (not the cheap thin crap)

We use the above three in motor termination boxes in nuclear installations and turbine installations. If it will survive the turbine install it will survive anything.


Bigger box and termination block in the box would be a better long term solution.

Joe Miranda said:

I have had a problem a couple of times with my current set-up. I am running a 15HP motor for my phase converter and the box where all the connections are made is quite small to cram all the wires in and I have had a problem with arcing.

Click to expand...

If the box in question is your main RPC enclosure you can bolt a smaller connection box to it and make your connections there. So if the RPC box is mounted on the wall, the connection box is underneath it. If you want to do it right then get the right size enclosure.

Wow...guys this was all really great help. I love all the suggestions. This is the box attached to the motor and it was never intended to house this much wire. I will definitely get a bigger box. I love the idea of the business cards in between - that's a definite keeper!

OK, I think we will get this resolved now.

Joe Miranda said:

I love the idea of the business cards in between - that's a definite keeper!

Click to expand...

If you are going to the bother of improvements, use genuine 'fish paper'. That's what it is meant for, and a little goes a long way.

Bill

CarlBoyd said:

Listen to Moonlight. Bigger box, Better tape...

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Yeah, the first time it happened it should have been fixed--the second time should never have happened. Also, as far as I know, joining ring connecters with a common bolt is not an approved method either. With a bigger box and proper connecters you should not need super tape to fix your problem. The mere fact that you're getting heat in a connection tells you there is something wrong. If you don't know what you're doing get an electrician to fix things before you cause a fire or injure someone...

ON the first layer of tape against the connection I always faced the sticky side of the tape out so if you ever want to change the connection the bolts and terminals are clean and not covered with glue. It was a good layer of approved # 33 vinyl electrical tape then a good layer of rubber tape and then another layer of vinyltape so you couldn't feel any sharp edges.

John