MTW vs. THHN 4

[robbm]

We're looking at replacing our control panel wiring (MTW wire) with THHN wire - which we already use in our conduit wiring. Does anyone know of a website that easily explains the differences between the two so that I can give my boss something to read to help him decide?? thanks in advance.

 

[dogleg43]

The NEC has tables listing what all of the different insulations mean.

MTW is great stuff, is easier to work with than THHN/THWN and has the same or better rating than THHN/THWN. Why not use it in the control panels?

 

[jraef]

Your wiremen will curse you. Basically they are the same, except the THHN has a thinner PVC layer and a nylon sheath around it to make it pull through conduit with less abrasion and improve its resistance to moisture, gas and oil that may leak into an underground conduit, none of which you should have in a control panel. That nylon sheath is a pain in the rear when you need to make 100's of connections in a control panel, you often must strip the sheath off before you can strip the insulation.

What was your reasoning?

http:/

http://www.jraef.com

Eng-Tips: Help for your job, not for your homework Read faq731-376

 

[robbm]

Yea, i know they're very close but my boss wants to trim the costs and space associated with keeping two sets of all our different wire colors and gauges. Right now we use MTW for our control panels and THHN (actually THHN/THWN) for our conduit runs. It seems to work just fine but the people deciding seem to think otherwise. I think using THHN all-over could be a problem inside the control panel, and using MTW all-over would be a problem in regards to the conduit. Oh well, thanks for the reinforcement...

 

[jraef]

Put it to them this way; using THHN in the panels will reduce the inventory and double the labor time. Should end the discussion.

http:/

http://www.jraef.com

Eng-Tips: Help for your job, not for your homework Read faq731-376

 

[bigbillnky]

Hello robbm,

Unless you need to practice your cursing, I would not recommend THHN. Control cabinets wired with THHN are very difficult to work in. When the wireway covers are removed and the wire disturb, THHN tends to "eject" itself from inside the wireway(and I do mean eject). This leaves the cabinet in a mess and makes tracing and replacing the wiring far more troublesome.

The only other difference I can think of that has not been mentioned above is the temperature rating. THHN is rated for 90* C, while MTW is available in 60* or 90* ratings.

Bigbillnky,C.E.F.....(Chief Electrical Flunky)

 

[REDDOG]

MTW Machine Tool Wire is only allowed for this purpose. It dress very nicely due to its flexiability. THHN/THWN/MTW is a general purpose insulation system for Field Wiring. As other post indicate it is a poor choice for Control Panel Interior Wiring. The Field Control Wires should be terminated in the panel to terminal blocks for transition to MTW wire which is conneted to Control components.