more flexible wire

Status
Not open for further replies.
dreamsville

dreamsville

Senior Member
Location
Michigan
Looking for a better wire than thhn for wiring in rigid conduit supplying large hp motors. I'm looking for something more flexible inside the peckerhead so that the insulation doesn't crack when you bend it around changing out motors and such.

I'm finding a lot of applications where the heat generated by these large motors is causing the insulation to become brittle after time.

Any help appreciated.
 
Cracking of the nylon sheath on THHN has absolutely no impact on the insulation of the conductor, if that is what you are worried about.
 
dreamsville said:
No. The underlying insulation is cracking through so as I can see bare copper.
Click to expand...
That is definitely bad.

Have you looked into using RHHW?
But as wire gets more flexible, it also gets larger in diameter, is there enough room in the motor terminal box?
 
There is enough room in the box. I have considered RHHW or maybe even XHHW. Not sure which would be better. I guess I need a wire insulation expert. Just thought I'd pick other brains and get their opinions or experiences. :smile:
 
Keep in mind that you are not really looking for 'more flexible wire', which generally implies finer stranding of the conductor itself.

What you are looking for is wire with insulation that doesn't degrade at the high temperatures encountered in the motor junction box.

Unfortunately, I don't know enough to point you further. The 'motor lead wire' that I've used (inside of motors, between the junction box and the coil head) was not rated as a type recognized by the NEC.

-Jon
 
If your motor circuits are in parallel any difference in length will show up much more than other parallel circuits
 
PFAH; 250c, 482f temp ratings, and high stress crack resistance.

max ampacity of #14 PFAH is 59 amps.
 
Dlo & sis

Dlo & sis

There are a couple options for wire with high strand count. The wire is flexible but I am concerned that your problem is overheating of the wire causing the insulation to become brittle. Flexible wire does not help. High temperature insulation is needed (PTFE) or better cooling.

DLO - diesel locomotive wire.

SIS - switchboard instrument systems

Both have very high strand count and are used where flexibility is required.
 
mtw

mtw

MTW is great have you tryed it. Dont know specs in conduit but in open cable tray and throughs in cabinets it is great for what ails you
 
finster1 said:
MTW is great have you tryed it. Dont know specs in conduit but in open cable tray and throughs in cabinets it is great for what ails you
Click to expand...

I don't believe MTW is listed for "general" type use, BUT locally I often get a wire that is labled MTW/THHN.

2002NEC Tbl 310.13 said:
MTW ... ... Machine tool wiring ... ...
Click to expand...

The only reason I made the statement above is that I've been chastised by powers that be for using MTW for just this application. I pretty much refuse to use standard THHN in a control cabinet, so I've was very happy to find the MTW/THHN, on accident, from my supplier.

See the link below as an example, no plug, just was at the top of the GoogleMonster's results page.
http://order.waytekwire.com/productdetail/M37/WN14-2

Regards,
Doug S.
 
Last edited:
Why is it getting so hot at the motor connections? It shouldn't be. If the insulation has gotten hot enough to damage it there is a problem with the wire size or the connections.

As far as using DLO, you can only use it in a NEC application if it is also listed as one of the type found in Article 310. I have used DLO/RHW for generators and motors a number of times to take advantage of the flexibility. Just remember that you can't use standard terminations on the fine stranded wire.
 
dreamsville said:
Looking for a better wire than thhn for wiring in rigid conduit supplying large hp motors. I'm looking for something more flexible inside the peckerhead so that the insulation doesn't crack when you bend it around changing out motors and such.

I'm finding a lot of applications where the heat generated by these large motors is causing the insulation to become brittle after time.

Any help appreciated.
Click to expand...

what voltage and hp range are you working with?

if you are looking for something to get from the disconnect to the
motor, diesel locomotive wire is extremely fine stranding, and a
jacket that is very rubbery, and flexes well.... however, it often
comes in odd sizes, like 929 MCM but the stuff is a serious slinky.
i've done cable bus with it, and you can do anything with it.

pricing? don't ask. it's bad. but, it'll work wonders...

if you are having cracking in the peckerhead, is there any chance
these motors are being used for plugging service? i've seen
that kill a 40 hp motor in a few days... just cooked the motor leads
in the peckerhead. the inrush current got things excessively hot.
 
I've terminated many motor junction boxes (peckerheads) with rigid, DLO and compression terminal lugs. That was before the factory switched to PVC jacketed MC for all the skids because of costs. The THHN conductors were 4/0 and difficult to work with after years of using DLO.

If don_resqcapt19 is right about the special lugs maybe you can use Polaris bugs.
 
jeremysterling said:
If don_resqcapt19 is right about the special lugs maybe you can use Polaris bugs.
Click to expand...

Read this document to get a little more info about the fine stranding issue. I personally avoided the issue on my photovoltaic project by using standard building wire, and all of our motors at the refinery are fed with THHN or XHHW so it's not an issue there either. If you have a hydraulic crimper there are Burndy and Ilsco lugs that are specifically listed and intended for use with fine stranded wire, so that's what I'd recommend if you have the crimp tool.
 
Dreamsville,

Why anyone would advise against using MTW in a motor application ?

We use MTW inside of control panels, exclusively.
I like the idea of TGGT, by SteveD, which I will be investigating.

I have seen the wiring taken from inside a SJOO cable
used for a short run into a hot motor.
This wire has very fine strands, the insulation is very rubbery and flexible.

Just out of rampant curiosity, using the SJOO cable,
I did a physical burn test, using flaming wood sticks,
and observed that the insulation charred badly,
but did not come apart, and did not burn.
I am sure that using a welders acetylene torch would do great heat damage,
that that would be extreme. You might try doing your own burn test.
Of course, my testing is NOT "UL listed and approved" !
So beware of your liabilities. You should be using a UL listed wire.

Just ideas to check out.

Hope you like these forums.

...
 
jdsmith said:
Read this document to get a little more info about the fine stranding issue. I personally avoided the issue on my photovoltaic project by using standard building wire, and all of our motors at the refinery are fed with THHN or XHHW so it's not an issue there either. If you have a hydraulic crimper there are Burndy and Ilsco lugs that are specifically listed and intended for use with fine stranded wire, so that's what I'd recommend if you have the crimp tool.
Click to expand...

Thanks for the link
 
Status
Not open for further replies.
Top