MTW wiring

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Fordean

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New Jersey
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Electrical Contractor
Been using MTW wire to terminate on load sides of disconnect Some equipment knockouts are like 1.5 in from lugs In which, stiff thhn is hard to bend snd terminate
Have remote underground connection
Is MTW rated for underground in pvc
I figure i can look this up but letting people know try mtw in these situations Maybe more expensive but works
 
I've always thought that MTW stands for machine tool wire.

Can it be used as general wiring?

I don't know if the W indicates wet, but I did see MTW wet rated.
 
MTW is sometimes more finely stranded, and that may be an issue for the ratings of some lugs. That's easily solved through use of properly crimped ferrules though.

MTW is basically THWN without the slippery outer nylon coating. As said above, it's not very slick, and can absolutely suck to pull into conduit.

www.awcwire.com

MTW vs THHN | Allied University

We exam the pros and cons of MTW vs THHN wires giving our detailed analysis and presenting the clear winner.
www.awcwire.com www.awcwire.com



SceneryDriver
 
My understanding is that MTW is rated for use inside of machinery and control cabinets, not for running in conduit and the like.

A previous post on this topic:

MTW TEW Wire

Hello and good day. I've got a 250 ft. spool of #10 AWG MTW/TEW 105 degree C, stranded wire came from a garage sale. The wire is in good shape. Can I use it in my house if I run it in EMT, to hook up my water heater? Thanks for your time.
forums.mikeholt.com

While flexibility is really nice for short jumpers in a cabinet, I think you will find you can easily use stiffer wires for longer runs; the increased length makes things naturally flexible.

Jon
 
winnie said:
My understanding is that MTW is rated for use inside of machinery and control cabinets, not for running in conduit and the like.

A previous post on this topic:

MTW TEW Wire

Hello and good day. I've got a 250 ft. spool of #10 AWG MTW/TEW 105 degree C, stranded wire came from a garage sale. The wire is in good shape. Can I use it in my house if I run it in EMT, to hook up my water heater? Thanks for your time.
forums.mikeholt.com

While flexibility is really nice for short jumpers in a cabinet, I think you will find you can easily use stiffer wires for longer runs; the increased length makes things naturally flexible.

Jon
Click to expand...
When wire enters cabinet u have only 2 inches
 
SceneryDriver said:
www.awcwire.com

MTW vs THHN | Allied University

We exam the pros and cons of MTW vs THHN wires giving our detailed analysis and presenting the clear winner.
www.awcwire.com www.awcwire.com
Click to expand...
From that article: "Both are built in accordance with the National Electrical Code for general purpose wiring for installation in conduits or other recognized raceways."

I hope so, because I have used it for generator control wires. It is wet rated to 60C (140F).
 
A search for "can MTW be pulled in conduit" brings up respectable claims in both directions. A couple of manufacturer statements that it is suitable for conduit, several different discussion threads going both ways. The most common suggestion is that the MTW is likely dual rated with a clearly acceptable conductor type. For example the THHN wire in my basement also claims to be MTW.

-Jon
 
MTW is listed as an allowed ch3 wiring type, but it has an application provision that says machine tool wiring, so that may restrict its use. Many manufacturers make a MTW dual rated THW -i'd just use that.
 
MTW CAN be used in conduit, although compared to THHN of the same AWG you are paying more for it to get extra flexibility (more strands), plus the insulation is twice as thick, which affects your fill calcs. MTW can have higher ampacities when sized per NFPA-79, but that does not apply once you leave the control panel, so you are back to NEC ampacity tables.

But more importantly IF it is a "wet" location or machine, MTW is only rated for 60C wet, even though it is rated 90C in dry. It's a little "gotcha" that got me once with an inspector. The only mention of that in the NEC is in Table 310.104(A). Where I got burned was that in my "wet" machine, I was using the 75C ampacities, but I got bounced on sizing the MTW that way since it could only be used at 60C.
 
Jraef said:
MTW CAN be used in conduit, although compared to THHN of the same AWG you are paying more for it to get extra flexibility (more strands), plus the insulation is twice as thick, which affects your fill calcs. MTW can have higher ampacities when sized per NFPA-79, but that does not apply once you leave the control panel, so you are back to NEC ampacity tables.

But more importantly IF it is a "wet" location or machine, MTW is only rated for 60C wet, even though it is rated 90C in dry. It's a little "gotcha" that got me once with an inspector. The only mention of that in the NEC is in Table 310.104(A). Where I got burned was that in my "wet" machine, I was using the 75C ampacities, but I got bounced on sizing the MTW that way since it could only be used at 60C.
Click to expand...
Where is the CAN be used in conduit? Seems like the application provisions in Table 310.104(A) limit to Machine Tools.
 
Jraef said:
310.10, MTW is listed for both dry / damp and wet locations. It mentions "any of the wiring methods covered in Chapter 3", which would inlude conduit.
Click to expand...
Right, but 310.10 references 310.104 which says it has to comply with the provisions, for MTW 310.104(A) says
Machine Tool Wiring in wet locations
Machine Tool Wiring in dry locations

Absent additional provisions that say
Wet location
Dry location
it seems as though the use is limited to Machine Tool Wiring.

310.10 Uses Permitted. The conductors described in 310.104
shall be permitted for use in any of the wiring methods covered
in Chapter 3 and as specified in their respective tables or as
permitted elsewhere in this Code.

310.104 Conductor Constructions and Applications. Insulated
conductors shall comply with the applicable provisions of Table
310.104(A) through Table 310.104(E).
 
Todd0x1 said:
Right, but 310.10 references 310.104 which says it has to comply with the provisions, for MTW 310.104(A) says
Machine Tool Wiring in wet locations
Machine Tool Wiring in dry locations

Absent additional provisions that say
Wet location
Dry location
it seems as though the use is limited to Machine Tool Wiring.

310.10 Uses Permitted. The conductors described in 310.104
shall be permitted for use in any of the wiring methods covered
in Chapter 3 and as specified in their respective tables or as
permitted elsewhere in this Code.

310.104 Conductor Constructions and Applications. Insulated
conductors shall comply with the applicable provisions of Table
310.104(A) through Table 310.104(E).
Click to expand...
I agree - if it is only marked MTW you are limited to Machine tool wiring.

If it has other markings, then it has more than one rating and any of those ratings marked can be used, 90 degree and wet location may not be allowed at same time unless it has a -2 designation though.

I'm pretty certain there is THHN/THWN out there that also has MTW marked on it.
 
So just to throw this out there. GE afcis have the neutral tail made out of MTW and that's all it says for insulation type. Idk if UL considers a panel a machine and yes it isn't pulled in conduit but it does show a separate respected entity accepting a use for that wire where not installed in a piece of machinery or in a whip to a piece of machinery.
 
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