MTW Wire sizing

[megloff11x]

I have some listed cable classified as MTW (Machine Tool Wiring) by UL. I'm going blind in the alphabet soup of wire types trying to find it for sizing calculations. It should fall under flexible cords and cables. I think the ratings given by the cable maker are a bit optimistic.

As an aside, I'd love for someone to publish a complete and concise guide to the ever increasing number of flavors of wire.

Matt

 

[celtic]

????

310.15(A)(1)
FPN No. 2:For the allowable ampacities of Type MTW wire, see Table 11 in NFPA 79-1997, Electrical Standard for Industrial Machinery.

or maybe eyeball T610.14(A)

That's all I found searching the '02 NECH.

 

[mdshunk]

MTW ampacities are almost identical to TFFN.

 

[peteo]

MTW is not found in the 2002 NEC (NFPA 70.) Its use was covered in a separate publication, NFPA 79 Electrical Standard for Industrial Machinery. No reason to think things have changed.

 

[ibew441dc]

It should fall under flexible cords and cables.

Matt

Megloff11x,

MTW is found in different sections thoughout the NEC 2005.

MTW is a designation givin to insulation of a conductor suitable for such use.

310.13 (2005NEC) and the UL WhiteBook agree that if MTW is in a dry location it is suitable for use at
90*C and in wet location at 60*C.

As far as the ampacity goes I would carfully read 110.14(C).

How old is the cable ? Most new cables have multaple ratings such as THHN,THW,MTW.

It is my opinion that you should use Table 310.16 when determining the ampacity. If you disagree I would recommend looking at 310.13 then 110.14(C) then 310.16.

hope this helped

Ibew441dc

 

[Pierre C Belarge]

Here is the info from NFPA 79, regarding the ampacity of MTW:

13.3.1
(1) MTW - Moisture, Heat, and Oil-Resistant Thermoplastic
60C (140F) Wet Locations
90C (194F) Dry Locations

Refer to Table 13.5.1 60C & 75C in 30C Ambient temperatures


some examples - not the complete table


1 AWG - 110A (60) 130A (75)
1/0 - 125A (60) 150A (75)
3/0 - 195A (60) 230A (75)
500 - 320A (60) 380A (75)

 

[GeorgeB]

I have some listed cable classified as MTW (Machine Tool Wiring) by UL. I'm going blind in the alphabet soup of wire types trying to find it for sizing calculations. It should fall under flexible cords and cables. I think the ratings given by the cable maker are a bit optimistic.

Matt

Cords and cables are assemblies of conductors; MTW is (IME) always a single conductor product. Most of what I have used, in control panel and conduit system wiring, is also rated THHN/THWN.

George (an electrical engineer, not an electrician, but expected to help install what my employer sold)