Table 310.20 & Messengers

[Ron Poehlmann]

I have a contractor wanting to apply table 210.20 to MC cable ampacity, and use the 90 Deg C column.

The 90 Deg C column issue is the easy part. 110.14(C) makes it clear that all of the terminations have to be rated for 90 Deg. C to use this column.

My questions is, what is a messenger?

From looking at other posts, it has something to do with overhead wire. I'm guessing the messenger is the steel wire in the cable to help carry the load. How close am I?

 

[benaround]

Ron, It is normally a seperate 'wire' , ie. not in a cable.

 

[Dennis Alwon]

From looking at other posts, it has something to do with overhead wire. I'm guessing the messenger is the steel wire in the cable to help carry the load. How close am I?

You are close. The poco usually pulls a triplex overhead to the service. In the bare wire there is a center core that is steel that is used to support the cable. That is the messenger wire.

Also the 90C column can be used even if the terminations are not 90C but you would be limited by the 75C column. This is good for derating wires. Starting at the 90C column allows us to use wires that would otherwise need to be a size larger.

 

[Ron Poehlmann]

Also the 90C column can be used even if the terminations are not 90C but you would be limited by the 75C column. This is good for derating wires. Starting at the 90C column allows us to use wires that would otherwise need to be a size larger.

Please explain further. How can you use the 90C column and not violate 110.14(C)? Everyone would love to use smaller wire to save $'s.