60' & 75' degree Terminal Ratings

Status
Not open for further replies.
J

jselectricservs

Member
Location
valinda c.a
Occupation
C10 Electrical Contractor
Hello,

I am for the first time doing some feeder calculations for some push button controllers that will operate some levelers. Ideally I would like to use the 75 degree column to size my conductors. On the push button diagram and on the disconnects say ( USE 60'/75' C Copper or Aluminum Wire ) does this mean I can use either.

Thank you.
 
The designation would allow 60° or 75° rated conductors. You would need to check the specific conductor for it's rating. For instance, MTW has one rating for dry locations and one for wet.
 
Thank you for your input and for TW reference. When doing things for the first time its easy to question yourself. glad this forum is here to help.
Thanks!
 
jselectricservs said:
Hello,

I am for the first time doing some feeder calculations for some push button controllers that will operate some levelers. Ideally I would like to use the 75 degree column to size my conductors. On the push button diagram and on the disconnects say ( USE 60'/75' C Copper or Aluminum Wire ) does this mean I can use either.

Thank you
Click to expand...

A dual rating of 60C / 75C gives you the most flexibility in this context. It allows for using 60C wire with 60C sizing, or 75C wire with 75C sizing. Anything beyond 75C (e.g. 90C-rated wire), will count as 75C rated wire for its termination, and as far as this specification is concerned. You can use the 90C rating for your derate calculations, but the termination ampacity is ultimately limited to 75C.

A rating that only mentions 75C, requires 75C rated wire, even if you aren't taking credit for 75C sizing. It wouldn't meet the manufacturer's requirements to connect 60C rated wire to such a terminal, even if you were using 60C sizing. This kind of rating, will strictly require wire that meets or exceeds 75C.

A rating that only mentions 60C, means any wire rated for temperatures above 60C, will require 60C sizing at the terminations. This also applies for unmarked equipment that is 100A and less. This rule is generally more academic than practical, since the vast majority of equipment is at least rated for 75C sizing. You still have a burden of proof to confirm this, from the product datasheets for equipment on both sides of the circuit.
 
jselectricservs said:
Thank you for your input and for TW reference. When doing things for the first time its easy to question yourself. glad this forum is here to help.
Thanks!
Click to expand...
don't confuse TW with MTW that was mentioned.

TW is for the most part older conductors that only had 60C insulation that are now using THHN/THWN rated conductors in their place today. Their insulation is much thicker and is kind of easy to spot because of that.

MTW is "machine tool wire" and has somewhat limited use unless it also carries other ratings.
 
Status
Not open for further replies.
Top