310.15 (A) when derating for CCC's

[Mustang125]

All I have always used the 90degree column when derating for CCC's or ambient but never really remembered why. I have been going back and forth with guys at work and they seem to believe that you must use the weakest point which is typically terminations at 60 or 75. I see were it says:


"the temp correction and adjustment factors shall be permitted to be applied to the ampacity for the temperature rating of the conductor, if the corrected and adjusted ampacity does not exceed the ampacity for the temperature rating of the termination in accordance with the provisions of 110.14(C)"

But this is about as clear as mud to most. it makes sense to me up until the point they say "if" haha. I especially don't understand what they mean by saying "ampacity does not exceed the ampacity for the temperature rating". Can someone really break this paragraph down for me?

I also watched a Mike Holt Video kind of about this and he said you use 90 no matter what, basically even if you are using TW or UF which is in 60 column, you still use 90?

 

[infinity]

You can use the conductor ampacity based on the insulation type. For example a 90° C conductor like THHN can be used at the 90° C ampacity for derating. After derating you're still stuck with the limits imposed by temperature rating of the terminal.

 

[Mustang125]

You can use the conductor ampacity based on the insulation type. For example a 90° C conductor like THHN can be used at the 90° C ampacity for derating. After derating you're still stuck with the limits imposed by temperature rating of the terminal.

meaning what tho? can you give me an example of when you derate for CCC's using the 90c when does the terminals rating come into play?

 

[Dennis Alwon]

As infinity stated... 90C for derating only but the final overcurrent device cannot be larger than the weakest link. For example, 12/2 nm cable has 90C conductors inside but is limited to 60C.

If you have 4 -12/2 cables together we must derate because of bundling. That would be 8 current carrying conductor's so 70% would be used based on the table.

12 @ 90C is rated 30 amps so we have 30 amps x .7 = 21 amps. Thus we can use a 20 amp breaker because that is not higher than the 60C rating.

The 90C insulation really helps when you need to derate.

 

[Mustang125]

so what your saying is if I had 10 current carrying I would have to use .5 which would bring be down to 15amps. so in that case id have to use a 15amp breaker. this seems obvious but not sure why that relates to terminals? this seems more to be about OCP. shouldn't it say "is not less than the ampacity of the OCP" instead of "does not exceed the ampacity of the temperature rating of termination"(this quote doesnt seem to make any sense to me, thats the route of my question)?


this is slightly off topic but what if the breaker specifically said 75degree on it? can I then use 75 or do i still have to go with 60 per 110.14(C)(1) for under 100a? think i answered my own question with "unless the equipment is listed and marked" but I wanted to double check i was reading it right?
As infinity stated... 90C for derating only but the final overcurrent device cannot be larger than the weakest link. For example, 12/2 nm cable has 90C conductors inside but is limited to 60C.

If you have 4 -12/2 cables together we must derate because of bundling. That would be 8 current carrying conductor's so 70% would be used based on the table.

12 @ 90C is rated 30 amps so we have 30 amps x .7 = 21 amps. Thus we can use a 20 amp breaker because that is not higher than the 60C rating.

The 90C insulation really helps when you need to derate.

 

[ActionDave]

so what your saying is if I had 10 current carrying I would have to use .5 which would bring be down to 15amps. so in that case id have to use a 15amp breaker. this seems obvious but not sure why that relates to terminals? this seems more to be about OCP. shouldn't it say "is not less than the ampacity of the OCP" instead of "does not exceed the ampacity of the temperature rating of termination"(this quote doesnt seem to make any sense to me, thats the route of my question)?

Because not all terminations are limited to 75⁰c

this is slightly off topic but what if the breaker specifically said 75degree on it? can I then use 75 or do i still have to go with 60 per 110.14(C)(1) for under 100a? think i answered my own question with "unless the equipment is listed and marked" but I wanted to double check i was reading it right?
As infinity stated... 90C for derating only but the final overcurrent device cannot be larger than the weakest link. For example, 12/2 nm cable has 90C conductors inside but is limited to 60C.

For Romex you are limited to 60⁰c

If you have 4 -12/2 cables together we must derate because of bundling. That would be 8 current carrying conductor's so 70% would be used based on the table.

12 @ 90C is rated 30 amps so we have 30 amps x .7 = 21 amps. Thus we can use a 20 amp breaker because that is not higher than the 60C rating.

The 90C insulation really helps when you need to derate.

Correct

 

[Mustang125]

i still dont understand what "does not exceed the ampacity of the temperature rating of the termination" means exactly. maybe im missing something haha sorry.

Why is romex limited to 60degrees? according to a cut sheet i found its insulation is rated for 90

 

[Dennis Alwon]

i still dont understand what "does not exceed the ampacity of the temperature rating of the termination" means exactly. maybe im missing something haha sorry.

Why is romex limited to 60degrees? according to a cut sheet i found its insulation is rated for 90

Look at art. 334 specifically 334.80 which tells us nm is not to exceed the 60C rating.

 

[Dennis Alwon]

so what your saying is if I had 10 current carrying I would have to use .5 which would bring be down to 15amps. so in that case id have to use a 15amp breaker. this seems obvious but not sure why that relates to terminals? this seems more to be about OCP. shouldn't it say "is not less than the ampacity of the OCP" instead of "does not exceed the ampacity of the temperature rating of termination"(this quote doesnt seem to make any sense to me, thats the route of my question)?


this is slightly off topic but what if the breaker specifically said 75degree on it? can I then use 75 or do i still have to go with 60 per 110.14(C)(1) for under 100a? think i answered my own question with "unless the equipment is listed and marked" but I wanted to double check i was reading it right?
As infinity stated... 90C for derating only but the final overcurrent device cannot be larger than the weakest link. For example, 12/2 nm cable has 90C conductors inside but is limited to 60C.

If you have 4 -12/2 cables together we must derate because of bundling. That would be 8 current carrying conductor's so 70% would be used based on the table.

12 @ 90C is rated 30 amps so we have 30 amps x .7 = 21 amps. Thus we can use a 20 amp breaker because that is not higher than the 60C rating.

The 90C insulation really helps when you need to derate.

It doesn't matter about the breaker if anything else in the chain is lower. The weakest link involves the entire circuit such as, the nm cable, terminations etc. Since nm is rated 60C , because the code says so, we must not use any ampacity over the 60C rating.

Your example with 10 nm current carrying conductor is correct. You are limited to 15 amps with the breaker.

 

[jap]

i still dont understand what "does not exceed the ampacity of the temperature rating of the termination" means exactly. maybe im missing something haha sorry.

Why is romex limited to 60degrees? according to a cut sheet i found its insulation is rated for 90

To realize the difference it might make , think of a different type of termination point other than breaker lugs.

A termination may be at a distribution block that has 90d rated terminals which would allow the 90d conductors at thier full capacity if not de-rated.

JAP>