Breaker Temperature Rating

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hill900505

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Hello,
Can a 75 degree C rated circuit breaker be installed with a 60 degree C insulation wire if the 60 degree wire is oversized for this application? Or we must use 75 degree C wire since it is marked this way on a circuit breaker?

Thanks for everyone's input.
 
hill900505 said:
Hello,
Can a 75 degree C rated circuit breaker be installed with a 60 degree C insulation wire if the 60 degree wire is oversized for this application? Or we must use 75 degree C wire since it is marked this way on a circuit breaker?

Thanks for everyone's input.
Click to expand...

Good question.

This is only the case when your circuit breaker is dual-rated for 60C/75C. This means you could use either
A. 60C sizing and 60C wire
B. 60C sizing and 75C wire
C. 75C sizing and 75C wire
D. 75C sizing and 90C+ wire

If your circuit breaker is straight rated for 75C, without carrying a dual 60C rating, your options are:
A. 60C sizing and 75C wire
B. 75C sizing and 75C Wire
C. 75C sizing and 90C+ wire

If your circuit breaker is straight rated for 60C, or if it doesn't carry any specific rating while being 100A and less, your options are as follows. Note that this is rare with modern equipment.
A. 60C sizing and 60C wire
B. 60C sizing and 75C wire
C. 60C sizing and 90C+ wire

In rare cases, you can use 90C termination sizing and 90C wire. Most if not all, manufactured equipment is limited to 75C in some form or another. Field-installed connectors (Polaris insulated tap blocks, insulation piercing connectors, split bolts) commonly are 90C, and if you install them in an enclosure separate from equipment, with a short segment of 90C wiring with 75C sizing, you can take advantage of the 90C rating for the main run. One reason you might do this, is if you screw up by forgetting to use 75C termination sizing, and need to remediate the situation. Another reason is that it could be a value-engineering decision.

This is explained in the following white paper:
http://www2.schneider-electric.com/...7/en_US/Wire Terminations 0110DB9901R2-02.pdf
 
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Thank you very much Carultch!!!
Still a little confused, say,a breaker only has 75 degree rating(No slash), if an oversized 60 degree C rated wire is used so that the terminal temperature will not exceed 75 degree C, to me, it is a safe installation for the breaker unless the reason is that the breaker terminal will reach 75 degree and cause the 60 degree C insulation to be damaged??
I read an article on http://www.schneider-electric.us/en/faqs/FA173839/ which says for a 80% rated breaker, the temperature rise above ambient temperature is 50 degree C which means a breaker terminal temp can reach up to 90 degree C in an ambient temperature of 40 degree, if that is the case, only 90 degree C insulation wire can be used.:?
 
hill900505 said:
Thank you very much Carultch!!!
Still a little confused, say,a breaker only has 75 degree rating(No slash), if an oversized 60 degree C rated wire is used so that the terminal temperature will not exceed 75 degree C, to me, it is a safe installation for the breaker unless the reason is that the breaker terminal will reach 75 degree and cause the 60 degree C insulation to be damaged??
I read an article on http://www.schneider-electric.us/en/faqs/FA173839/ which says for a 80% rated breaker, the temperature rise above ambient temperature is 50 degree C which means a breaker terminal temp can reach up to 90 degree C in an ambient temperature of 40 degree, if that is the case, only 90 degree C insulation wire can be used.:?
Click to expand...


If there is no dual rating, and it is straight-rated for only 75C, that means no 60C wiring of any size, can connect directly to it. The idea is that heat generated inside the unit can cause the temperature at the terminal to exceed 60C, and therefore thermally conduct to the 60C insulation, thus melting it.

So if equipment carries a straight 75C rating, you have to use wire with a 75C insulation temperature rating or greater, even if you are connecting #6 on a 15A circuit. If you want to connect to 60C wire eventually, you have to start with 75C or 90C wire at the breaker, and then splice it to 60C wire in another enclosure.

Most modern wire is 90C rated anyway, so the need to care about the 60C rating is mostly academic. It will apply when you are working with old equipment or old wire, made before the higher temperature rated products originated. Romex cable (NM cable) and UF cable require you to use 60C sizing, and SE cable requires 60C termination sizing if routed in thermal insulation, but most cables in these families that you will find manufactured today, actually carry either a 75C or 90C rating that allows you to connect them to 75C straight rated breakers.
 
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Nice descriptions Carultch. :)

Carultch said:
If there is no dual rating, and it is straight-rated for only 75C, that means no 60C wiring of any size, can connect directly to it. The idea is that heat generated inside the unit can cause the temperature at the terminal to exceed 60C, and therefore thermally conduct to the 60C insulation, thus melting it.
Click to expand...

^^^^ This ^^^^
​

In my opinion that fact is an important thing to have in the back of your mind. Once you realize that the copper or aluminum conductor is being used as a heat sink to pull heat out of the thermal magnetic breaker the sizing / temperature rules start to make sense.

To illustrate this further, in some cases the manufacturer may require you use 90 C or better wire but apply it as 75C wire.

Carultch said:
Most modern wire is 90C rated anyway, so the need to care about the 60C rating is mostly academic.
Click to expand...

For what it is worth modern NM (Romex) is rated 90 C but we are required to treat it as 60 C for ampacity calculations. NEC 334.80
 
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iwire said:
...
To illustrate this further, in some cases the manufacturer may require you use 90 C or better wire but apply it as 75C wire.
...
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That is the case for a 100%-rated assembly where continuous loading is not factored 125% and the full breaker rating can be used for continuous load circuits.
 
Smart $ said:
That is the case for a 100%-rated assembly where continuous loading is not factored 125% and the full breaker rating can be used for continuous load circuits.
Click to expand...

I believe it is the case if you use a specific breaker regardless of how you choose to load it.
 
hill900505 said:
Hello,
Can a 75 degree C rated circuit breaker be installed with a 60 degree C insulation wire if the 60 degree wire is oversized for this application? Or we must use 75 degree C wire since it is marked this way on a circuit breaker?

Thanks for everyone's input.
Click to expand...
We deal with this kind of thing nearly all the time, though it is usually 90 degree conductors on either 60 or 75 degree terminations.

Simple fact is if the termination is only 60 degrees rated then you must select the conductor size using the 60 degree ampacity table regardless of the insulation rating on the conductor. 240.4(D) kind of puts us at 15, 20 and 30 amps for 14-10 AWG regardless in most applications, but take 8 AWG, if the terminal is only rated 60 deg, then you must limit it to 40 amps even though it has 90 deg insulation which is rated for 55 amps. You can use that 55 amp value for ampacity adjustments say for high ambient temperature or more then thee current carrying conductors in a raceway, even if you have 60 deg terminations.
 
iwire said:
I believe it is the case if you use a specific breaker regardless of how you choose to load it.
Click to expand...
Perhaps.

My statement was in regard to using the Exceptions to 210.19(A)(1)...

Exception: If the assembly, including the overcurrent devices
protecting the branch circuit(s), is listed for operation
at 100 percent of its rating, the allowable ampacity of the
branch-circuit conductors shall be permitted to be not less
than the sum of the continuous load plus the noncontinuous
load.
Click to expand...

...and 210.20(A), for example.

Exception: Where the assembly, including the overcurrent
devices protecting the branch circuit(s), is listed for operation
at 100 percent of its rating, the ampere rating of the
overcurrent device shall be permitted to be not less than the
sum of the continuous load plus the noncontinuous load.
Click to expand...


Code does not specifically require 90°C-rated conductors, but the 100%-rated equipment instructions do.
 
Smart $ said:
Code does not specifically require 90°C-rated conductors, but the 100%-rated equipment instructions do.
Click to expand...

And I am not disputing what the code says in the least.

What I am saying is that with say a Sq D 3,000 amp breaker the instructions required 90 C conductors applied at 75C and I would say that applies if the design loads the breaker to 10% or 100%.
 
iwire said:
And I am not disputing what the code says in the least.

What I am saying is that with say a Sq D 3,000 amp breaker the instructions required 90 C conductors applied at 75C and I would say that applies if the design loads the breaker to 10% or 100%.
Click to expand...
My reply does not nor was it intended to challenge your statement. Please stop thinking every time I reply to one of your posts that I am challenging you.
 
Smart $ said:
My reply does not nor was it intended to challenge your statement. Please stop thinking every time I reply to one of your posts that I am challenging you.
Click to expand...

When you quote someone .... and you are you .... you can expect that is how it is taken. :D
 
Smart $ said:
I see you do... when you are you. :happyyes:


I am always me and I do not. :happyno:
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He gives me a hard time for quoting things too.

I often do it so I can look at the content I am replying to when composing a post, not necessarily trying to challenge anything with a lot of them.
 
kwired said:
He gives me a hard time for quoting things too.

I often do it so I can look at the content I am replying to when composing a post, not necessarily trying to challenge anything with a lot of them.
Click to expand...

OK, you want to talk about it? I am game.:D

No, I do not give you a hard time for 'quoting things'. That is not the case at all.

I, and some others give you a hard time for quoting someone and basically repeating what they said in your own words. :p
 
iwire said:
OK, you want to talk about it? I am game.:D

No, I do not give you a hard time for 'quoting things'. That is not the case at all.

I, and some others give you a hard time for quoting someone and basically repeating what they said in your own words. :p
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I don't have any of my own words, I've been using the same words most everyone else uses.:)

Have to credit George Carlin to some extent for that comment
 
Carultch said:
Quote Originally Posted by iwire View Post
I, and some others give you a hard time for quoting someone and basically repeating what they said in your own arrangement and selection of words.

;)
Click to expand...

Were you just fixing that for him or were you doing what I was being accused of?

:ashamed1:
 
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