The old 60/75 degree issue

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cleveland

Member
Location
Midwest
We recently had a bru-hah-hah between a contractor doing work for us and the consulting engineer who designed the job. The issue was the feeders to an AHU with electric reheat. The unit came in with nameplate ratings different from what was indicated on the plans. All this was on feeders less than 100 amps. The result was the belief for needing one size larger wire for one of the feeders to the unit. Since the unit had 75 degree ratings on its terminations the consultant said we could use the 75 degree ampacity column in the NEC. This would allow for the wire to remain as he sized it. I got to be the good/bad guy to make a call and said let's increase the wire size. This was based on the fact I wasn't sure just what the rating of the terminations at the head end of the feeder was. We were feeding this unit from a 40 year old panel. So I was not sure we didn't have 60 degree termination limitation there. Was this a good call, bad call, or not sure call? And no I did not go and rip of the panel cover off to verify the 40 year old breaker terminations; arc flash hazards you know!

Thanks for your time,

Jim
 

raider1

Senior Member
Staff member
Location
Logan, Utah
The only way to know if this is a good or bad call would be to check the temperature ratings of the breaker supplying the feeder.

Chris
 

charlie b

Moderator
Staff member
Location
Lockport, IL
Occupation
Retired Electrical Engineer
Of course it was a good call. Engineers don't make bad calls! ;)

I would have arranged for an electrician to inspect the panel and determine, if possible, the rating of the terminations. Absent certain proof that they are rated for 75C or higher, I would have to presume they are not, and that the 60C ampacity limit would apply.

By the way, what was your role on this project? Owner's representative?
 

steve66

Senior Member
Location
Illinois
Occupation
Engineer
Hypothetical question: Say the breaker is only rated for 60 degrees, so the larger wire is required.

Could the contractor install a short piece of the larger wire, and then use a connector listed for 75 degrees, and then run the smaller wire out to the heater??
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
Hypothetical question: Say the breaker is only rated for 60 degrees, so the larger wire is required.

Could the contractor install a short piece of the larger wire, and then use a connector listed for 75 degrees, and then run the smaller wire out to the heater??

Hypothetical answer: yes.
Real-life answer: I've used CU/AL splices for connecting aluminum cable to copper-only terminals.
 
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