60/75C Breaker Inception

bradbb2005

Member
Location
South Carolina
Occupation
Electrical Designer
I am curious if anyone knows about when 60/75 C dual-rated smaller breakers became common or if it has always been so. We design a lot of renovations for the government where we reuse panels that could be from the '80s or earlier and there is no requirement nor desire to upgrade these panels. Sometimes we simply don't know the rating of the breakers that could potentially be reused and if it were only rated for 60C, we would need to adjust our ampacity selection. I understand a new breaker would most likely be rated 60/75C but really just wondering if there is a time where it was common to not have the 60/75C rating. Yes, we could pull the cover off and look at the breakers but usually, that is not feasible at the time of site survey. Also, this is D-B work and I know most would say upgrade everything, that just isn't how these projects work.

Thanks!
 

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
Retired Electrical Engineer - Power Systems
I looked at some Square D data sheets, from 1966, none of them mentioned a terminal temperature rating.
I recall the 60/75C rating in 1978.
 

kwired

Electron manager
Location
NE Nebraska
For the most part it really doesn't matter presuming those old circuits were properly designed when they were new.

If they only had 60 degree conductors the conductor ampacity had to be based on 60 degree ampacity tables, if you replace an existing 60C rated breaker with one that is rated up to 75, you haven't created any problem.

What you need to maybe look out for is repurposing existing conductors and make sure you don't use 75 C ampacity on a conductor that is only rated 60C or to take it beyond terminal temp rating make sure you don't adjust ampacity where you have ambient temp or multiple conductors in same raceway using the 90C ampacity table like you normally can with "all new" conductors.
 

Jraef

Moderator
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
For the most part it really doesn't matter presuming those old circuits were properly designed when they were new.

If they only had 60 degree conductors the conductor ampacity had to be based on 60 degree ampacity tables, if you replace an existing 60C rated breaker with one that is rated up to 75, you haven't created any problem.

What you need to maybe look out for is repurposing existing conductors and make sure you don't use 75 C ampacity on a conductor that is only rated 60C or to take it beyond terminal temp rating make sure you don't adjust ampacity where you have ambient temp or multiple conductors in same raceway using the 90C ampacity table like you normally can with "all new" conductors.
I took his comment to mean they want to repurpose the old breakers, but are running new wiring and want to be able to use 75C ampacities.

If that’s the case, I don’t see how you could do that without actually seeing a 75C rating on the old breaker. regardless of what anyone thinks, there is not going to be a universally acceptable date range in which all breakers were switched to 60/75C terminals. It will have happened over time within each brand and each brand will have a different starting point.

Even to this day, UL489 for breakers still just says “All circuit breakers rated 125 A or less are marked for use with 60° C, 60/75°C or 75°C only wire.”, meaning that technically a new breaker could still have 60C only markings. That would be poor marketing now, I’m only pointing it out that there was never an “official” start date for the 60/75C markings.
 

bradbb2005

Member
Location
South Carolina
Occupation
Electrical Designer
I took his comment to mean they want to repurpose the old breakers, but are running new wiring and want to be able to use 75C ampacities.

If that’s the case, I don’t see how you could do that without actually seeing a 75C rating on the old breaker. regardless of what anyone thinks, there is not going to be a universally acceptable date range in which all breakers were switched to 60/75C terminals. It will have happened over time within each brand and each brand will have a different starting point.

Even to this day, UL489 for breakers still just says “All circuit breakers rated 125 A or less are marked for use with 60° C, 60/75°C or 75°C only wire.”, meaning that technically a new breaker could still have 60C only markings. That would be poor marketing now, I’m only pointing it out that there was never an “official” start date for the 60/75C markings.
Exactly. I did see that reference in 489. You are also dead on with the intent. I think overall any replacement (new) breakers provided on these projects will be 60/75C and we do specify to use new breakers but sometimes the government reviewers are questioning it and the contractors do reuse breakers. I hate to size everything @ 60C, especially for something like HVAC just because I cannot prove that the feed breaker is rated for 60/75.

On newer panels, the resources are still somewhat available but on panels dating back from the '70s and '80s, or earlier, specs sheets are hard to come by. I was just hoping to know if there was a semi-definitive time period where 60C only became widely uncommon.

The panel in question was a Westinghouse Q22B42CKT panel, which I believe will accept BAB breakers and I can see on supply sites that they are 60/75C rated, so I am standing on the fact that we can size applicable circuits to 75C but also indicating the contractor must confirm ratings prior to installing.

Thanks again.
 
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