MI cable ampacity

[hockey]

The 500MCM mineral-insulated cable we have specified has a table 310.16 ampacity of 430A at 90 degrees-C. However, the terminations are only rated for 75 degrees-C. How do I derate the ampacity of the cables?

 

[iwire]

Re: MI cable ampacity

Just use the 75 C column.

This is no different than when you use THHN which is 90 C but will be connected to 75 C terminals.


By the way, have fun running it.

 

[badjeepr]

Re: MI cable ampacity

i believe the 90 degree column may always be used for derating purposes but for actual ampacity rating one must use the lowest applicable temp. range

 

[iwire]

Re: MI cable ampacity

Originally posted by badjeepr:
i believe the 90 degree column may always be used for derating purposes but for actual ampacity rating one must use the lowest applicable temp. range

Yes if you are actually using Table 310.15(B)(2)(a) with 90 C conductors you can start at the 90 C column.

I am going to be surprised if that is what is going on here. I strongly doubt he has more than 3 - 500 kcmil MIs in one raceway.

[ September 06, 2005, 04:39 PM: Message edited by: iwire ]

 

[petersonra]

Re: MI cable ampacity

I remember we had a former engineer once ordered some MI cable intending to use it basically as an extension cord.

Note use of word former.