Terminal Temperature Ratings

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A/A Fuel GTX

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I'm wondering why manufacturers can't just produce terminals rated at 90 degrees C as a standard. It would sure be nice if we could get full ampacity out of our conductors rather than having to derate due to the 75 degree C lugs, breaker terminals etc. that seem to be the norm. Any thoughts?
 

ron

Senior Member
Re: Terminal Temperature Ratings

Tom,
Oddly enough, many terminals are rated at 90 degrees C on their own. When the terminal is attached to a breaker or switchboard/switchgear bus, it is only tested at 75 degrees, so they can only be used at 75 degrees.
 

A/A Fuel GTX

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Re: Terminal Temperature Ratings

Originally posted by iwire:
Not to sure I want my wiring to be running at 195 F.
Bob, I don't understand your comment. Are you saying the wire temp could reach 195 F or you don't want to run your wire in an ambient of 195 F? If the wire is properly sized and the insulation is rated at 194 F, why give up all that ampacity due to 167 F terminals?

[ February 22, 2006, 02:50 PM: Message edited by: m73214 ]
 

iwire

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Re: Terminal Temperature Ratings

Would you want the terminal on a breaker and the conductor connected to it to be operating at 195F?

In the case of a breaker that may make it difficult for the thermal trip to do it's job.

There is also other issues to consider such as voltage drop, if we tried using conductors at the 90 C rating we would find that voltage drop is more of a problem.
 

A/A Fuel GTX

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Re: Terminal Temperature Ratings

I guess my point is that if the wire and the terminals were properly sized for load and temperature the actual temperature of the conductors and terminals would not be anywhere near the maximum rating.
 

iwire

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Re: Terminal Temperature Ratings

Originally posted by m73214:
I guess my point is that if the wire and the terminals were properly sized for load and temperature the actual temperature of the conductors and terminals would not be anywhere near the maximum rating.
Actually the conductors could approach 90 C if used at the 90 C rating.

Obviously it is unusual to actually load a wire right to it's ampacity rating but the code is written with worst case in mind. IMO.

Bob
 

jim dungar

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Re: Terminal Temperature Ratings

Terminations due not run any where near the temperarture of the conductor insulation nor that of the individual lug.

According to a 1986 standard "...at 100% of marked current rating of the circuit breaker. ... Temperature rises shall not exceed 60C where connections are made to ...wiring terminals ... If temperature rises on wiring terminals exceed 50C, the manufacturer shall specify that wire rated 90C sized per [75C] must be used."
 

iwire

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Re: Terminal Temperature Ratings

OK, but that standard would be difficult to achieve if the conductor connected to the terminal was run at its 90 C rating would it not?
 

iwire

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Re: Terminal Temperature Ratings

I guess my thought was this.

Right now with the rules and equipment we use now if I feel a warm raceway or panel I take note of it and wonder if all is well.

If we raised the limits another 15 C we would find warmer raceways.

I personally do not see any good to be had from basically loosening up the rules we have now.
 

bphgravity

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Location
Florida
Re: Terminal Temperature Ratings

The heat generated by current flow in conductors is a loss (I?R). The loading of conductors to 90? would only serve to increase the inefficiency of our electrical systems. Cooler = Better. This goes back to the the old question of what would be better, a super-conductor or a super-insulation?

Besides, how would OSHA feel about 194? F cables and raceways exposed to contact?
 

A/A Fuel GTX

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Re: Terminal Temperature Ratings

I see your point Bob but I'm looking at it from this perspective. If the conduit is warm, it may be from running conductors at more than 80% of their ampacity rating or improper derating due to number of conductors. Can we assume that if 310.16 says we can load a # 8 THHN to 55A, that would be a safe circuit that would not feel warm to the touch? Are those amp ratings the absolute maximum or ratings that should not produce adverse heating? And even if the conduit is warm, that wouldn't necessarily mean the terminals in the panel are warm.
 

iwire

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Re: Terminal Temperature Ratings

Originally posted by m73214:
If the conduit is warm, it may be from running conductors at more than 80% of their ampacity rating
The code allows running conductors at 100% of their ratings unless the maximum load will last more than 3 hours.

I am over my head on the engineering end of this but I have seen a lot of different installations and failures I just can't see that running the conductors 'harder' would be beneficial to the consumer.
 

charlie b

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Re: Terminal Temperature Ratings

Originally posted by bphgravity:Besides, how would OSHA feel about 194? F cables and raceways exposed to contact?
Probably a bit more concerned, but not a great deal more concerned, then they would feel about 167? F (75 ? C) cables and raceways exposed to contact.

But this is not a human issue. The entire purpose of imposing ampacity limits is to protect the integrity of the conductor's insulation system and the integrity of any termination to which the conductor is connected. If the anticipated I^2R heating in a given conductor size appers to be too high, and if you want to keep the same current, then you need to get a bigger wire. Then the same "I" gives you a lower I^2R, because the bigger wire has a lower "R."
 

don_resqcapt19

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Re: Terminal Temperature Ratings

It is my understanding that if you run the conductors at their rated ampacity under the conditons given in the ampacity table, then the copper will reach the rated temperature.
Don
 
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