NFPA 79 - wire nuts not suitable for motor connections ? 5

[steelerr]

In NFPA 79-2007, Clause 13.5.9.2 states, "Electrical connections at motor terminal boxes shall be made with an identified method of connection. Twist-on wire connections shall not be used for this purpose."

What I think this means that wire nuts cannot be used in motor 'peckerheads'. Other than European (CE-Marked) motors, I've never seen anything other than wire nuts with or without electrical tape wrap for making these connections.

Which US motor manufacturers offer terminal strips or connecting studs in the peckerhead?

Alternately, what "identified" methods exist for this conection? I'm having difficulty finding suitable connectors that won't cost a fortune to implement, or that will fit three into a typical peckerhead.

Thank you.

 

[oldfieldguy]

'Way back in history, before NFPA 79, we used wirenuts at one facility I worked at. I never had a problem with them IF INSTALLED CORRECTLY, but from failures I investigated, installing them correctly was a problem.

The last time I had to to the installation of a sizable number of 480-volt motors, we used ring terminals on all the leads, and connected the rings together with appropriately sized nuts and bolts or screws, and then taped the connections over.

Again it was a given fact that some people could mess up this installation.

On some larger motors, I've seen cable to cable connections made with split-bolts.

In any method, a high level of care is needed to produce satisfactory results.

old field guy

 

[peebee]

Wow, red star just for bringing this to my attention. Never heard of this (probably because I've never even cracked 79 before).

There are crimp-on connectors that look a lot like wire nuts, perhaps that's what you've seen in those motors? But more likely, your electricians are no more familiar with this requirement than I was -- or maybe they've heard the requirement but think they're smarter than the NFPA.....

 

[jraef]

I know of no industrial facility with an established engineering protocol that allows wire nuts to be used anywhere other than in office wiring junction boxes and even some of them don't allow that either. In my old circles of field work, one could be fired for making up a motor with wire nuts! Split bolts (kearnies) or ring tongues + screws, nuts and washers as oldfieldguy mentioned is the established norm for smaller motors. Then wrapped by varnished cambric tape to protect the connection from glue on the next stages, wrapped again with rubber splicing tape to protect the connection from vibration, then finally with PVC electrician's tape to protect the rubber from contaminants. Most large motors have termination boxes with landing studs.

 

[steelerr]

Thanks for the valuable input.
Since my original post, I've come across a couple of commercially-available alternatives to wiring nuts:

http://energy.tycoelectronics.com/rrg/raychem_rrg/130.pdf

http://www-public.tnb.com/ps/endeca/index.cgi

These type connectors takes the skill out of the terminations that oldfieldguy referred to.
I've also seen some 1000V shrink-wrap mat'l that can be used over the ring terminals bolted together. I wonder if I can replace the whole taping routine with this.

http://www-public.tnb.com/contractor/docs/shrinkon.pdf

Thanks again.

Bob Steele
Electrical Designer

http://www.gala-industries.com

 

[resqcapt19]

Bob,
I use the GelCaps when I can, they work great and are cost effective compared to using tape. The only problem is that they are too big for small motors.
Don

 

[oldfieldguy]

steelerr--

Just remember that you can't make things foolproof... fools are on a program of continuous innovation and improvement...

there are many methods of connection that will work well iff applied carefully by knowledgeable people. No method will work if applied carelessly...

good luck!

old field guy

 

[MagneticFlux]

If "wire nuts" are not suitable for connecting the motor lead(s) to its branch circuit conductor(s), then why is it acceptable to use them at any point of the branch circuit? (i.e. in an junction/splice box)

 

[dpc]

For one thing, those are probably covered by a different code than the NFPA 79 referred to in the OP.

From a practical standpoint, motor terminal boxes are subject to a lot of vibration that normal junction boxes are not subject to, so it makes sense that tougher standards might apply to motor terminals.

Wire nuts are generally not a good choice for stranded wiring, in any application.

 

[peebee]

Re: Wire nuts are generally not a good choice for stranded wiring, in any application.

That may or may not be the case... but they are certainly THE standard choice for many many applications -- in fact, you most likely have some in your very own home, unless you personally installed or inspected inspected each and every splice.

 

[jraef]

There are lots of ways of doing things that are "not prohibited", but that does not make them the right way to do them. I use wire nuts in my house when connecting solid wire in a junction box, and maybe when I'm connecting stranded fixture wire to a solid wire for a light fixture etc.

But I have never EVER seen a qualified industrial electrician use wire nuts unless on anything that requires 14ga wire or greater, unless it was a temporary test or emergency restart situation where they knew they were going to come back and do it right when they had time. Industrial applications are typically subjected to more vibration, modification and exposure to corrosive influences than anything you will see in a residential location.

 

[dpc]

Right, I don't have a problem with wire nuts for solid (copper)wire - lighting and receptacles. This is standard practice.

I have very little stranded wire in my house, and certainly use wire nuts at home when the need arises.

I usually don't consider residential work in this forum.

 

[controlsdude]

If this is the case I would think motor manufacturers would either give recommendations on what is proper, or give a terminal strip in their peckerhead.

When I look at a motor manufacturers website I do not see recommended ways on termination in their peckerhead?

Why is this the case?

Can anyone give me an example where the motor manufacturer has recommended this or that based on the above code?

 

[sreid]

Is it possible that wire nuts are not allowed is that the motor wiring is stranded and the electrical service is solid core. I beleive that wire nuts woud be terrible for a solid/stranded appliciation.

 

[electricpete]

It's an interesting question. I'm pretty sure it's an approved method for homes. The ceiling fan that I put in awhile back came with wire nuts in the box.

I don't know about commerical building wiring.

I know for sure at our industrial plant the electricians never use wire nuts.

If you think about what prevents the wire nut from untwisting, it seems like it's not a lot. I guess there is some kind of friction device inside that clamps to the conductors... to be honest I don't know how it works. From that perspective, a bolted connection certainly seems preferable.

Strange that we consider various machinery where we work to be critical, but we don't consider the connections in the wall where our familiy sleeps to be as critical?

=====================================
Eng-tips forums: The best place on the web for engineering discussions.

 

[peebee]

dpc & electricpete -- your guys don't even use wire nuts for 2x4 fluorescent light fixtures in your office areas?

 

[peebee]

Re: "I'm pretty sure it's an approved method for homes. "

You seem to be correct, electricpete. Per NFPA 79 1.3.2: "This standard shall not apply to the following: ... (2) Machines used in dwelling units"

 

[peebee]

Strange, a Google search on "motor wire nut" and other similar searches turns up very little (this thread is #1).

One of the top results is an article discussing all the fires experienced at one facility until they stopped using wire nuts, and the question was posted what others thought of wire nuts and other options.

There doesn't seem to be much general awareness of NFPA 79 13.5.9.2.

It's a shame that this requirement is not repeated in the NEC (NFPA sure repeats plenty of other stuff), that would probably lead to much greater compliance (and fewer fires).

 

[peebee]

sreid:

Regarding: "Is it possible that wire nuts are not allowed is that the motor wiring is stranded and the electrical service is solid core. I beleive that wire nuts woud be terrible for a solid/stranded appliciation."

As electricpete said, his ceiling fan came with wirenuts in the box -- most any electrical equipment (lamps, fans, etc) you buy from Home Depot or Lowe's will come with wire nuts in the box. I realize that most industrial plants don't buy their stuff from HD.... but the question is not regarding industry standard but rather code requirements.

Presumably HD's vendors realize that most people have #14-#12 solid wire in their homes, but apparently they have no issue with the use of wire nuts (not just any wire nuts either... those are the cheapest smallest no-spring 100%-plastic nuts you will find anywhere on the planet). So presumably it is OK to use wire nuts for stranded/solid connections.

 

[dpc]

We allow solid copper wire and wire nuts for lighting and receptacle circuits in office areas and commercial buildings. Some utility clients do not allow this at all and we have changed our specs for them.

I don't think any of this is an NEC violation provided the wire nuts are listed for use with stranded and/or solid wire of the appropriate sizes and quantities. If you look on a box of wire nuts, it will have a table of acceptable use and the combinations of wires (stranded or solid) that can be used.