Separate enclosure for upsizing wires to due termination temperature limitations

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YaakYaak

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Indiana
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Electrician
Hi guys, long time reader, first time poster here :) I appreciate all the knowledge, shared in a kind and clear way. It's rare to see such helpful and pleasant forums nowadays...
I've seen on this forum multiple times that if you are using 90C rated wire at its 90C amperage rating (e.g. #12 THHN for 30A), and you want to upsize the conductor in order to terminate it in 75C terminals (in this case, from #12 to #10), you need to make those splices using 90C connectors "in a separate, otherwise empty enclosure".
I assume the reason it has to be a separate enclosure is because you can't have the temperature exceeding the terminal's rating anywhere within the terminal's enclosure, in order to not overheat the terminal itself. Therefore you need to keep the conductor that may possibly reach 90C out of an enclosure with 75C terminals.
I do not understand why the separate enclosure has to be "otherwise empty". I also couldn't find this anywhere in the NEC, although I will admit that my code proficiency is work in progress...
The only thing I could think of is that "otherwise empty" just means "empty of anything with a lower temperature rating", rather than "empty of other splices and conductors passing through". Is this the correct answer or is there something else going on that I'm missing?
 
I've seen it on multiple threads on this forum. I am having a hard time finding it at this point . If that term (or concept) doesn't exist or apply, that answers my question as well!
Is there any need for the splices to be in an empty separate enclosure, or can you put them inside any junction box without devices or terminals rated below 90C?
 
YaakYaak said:
I've seen it on multiple threads on this forum. I am having a hard time finding it at this point . If that term (or concept) doesn't exist or apply, that answers my question as well!
Is there any need for the splices to be in an empty separate enclosure, or can you put them inside any junction box without devices or terminals rated below 90C?
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That language is not in the code.
210.19(A)
Exception to (1) and (2):
Where a portion of a branch circuit is connected at both its supply and load ends to separately installed pressure connections as covered in 110.14(C)(2), an allowable ampacity in accordance with 310.15 not less than the sum of the continuous load plus the noncontinuous load shall be permitted. No portion of a branch circuit installed under this exception shall extend into an enclosure containing either the branch-circuit supply or the branch-circuit load terminations.
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While it does not specifically say that you can't have other circuits in the enclosure, you could read the last sentence as implying that.
 
don_resqcapt19 said:
While it does not specifically say that you can't have other circuits in the enclosure, you could read the last sentence as implying that.
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I read the last sentence as saying you need to keep the 90°C conductors out of the same enclosure as the lower temp device terminations. It says nothing about conductors for other devices.
 
jim dungar said:
I read the last sentence as saying you need to keep the 90°C conductors out of the same enclosure as the lower temp device terminations. It says nothing about conductors for other devices.
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Yes that is what is says, but I can see others reading as saying it applies to all conductors operating at less than 90°C.
 
don_resqcapt19 said:
Yes that is what is says, but I can see others reading as saying it applies to all conductors operating at less than 90°C.
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Like the other conductors must have 90°C insulation?

Do we require conductors 'running at' 60°C to be separated from those at 75°C? This would be a real hassle in a load center.
 
jim dungar said:
Like the other conductors must have 90°C insulation?

Do we require conductors 'running at' 60°C to be separated from those at 75°C? This would be a real hassle in a load center.
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not sure...just have seen other comments similar to the one in this thread and just suggesting a possible reason, even though the code does not say this
 
Thank you for the help. In my case, there is an existing separate enclosure that has very many conductors running through it. (Not enough to get anywhere close to the maximum fill of the enclosure, as the enclosure is also very large for the application.) All the conductors (as far as I can see) are THHN, so even according to Don's possible reading that Don and Jim both don't think is correct I shouldn't have a problem.
 
I have had some suggest to me that if you went into a panel with 75C conductors (new circuit) running at 75C and the panel had 60C conductors that the whole panel must be brought up to 75C.

Is why I always size conductors at 60C
 
Eddie702 said:
I have had some suggest to me that if you went into a panel with 75C conductors (new circuit) running at 75C and the panel had 60C conductors that the whole panel must be brought up to 75C.

Is why I always size conductors at 60C
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Even for circuits above 100A?
 
petersonra said:
I hate when the code authors refuse to use plain English. How is anyone supposed to abide by any instructions that are this badly written.
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I don't think it is badly written.
The exception language says the 90°C conductors cannot be in an enclosure with any of the device terminations rated at lower temperatures. It says absolutely nothing about other conductors or items.
 
YaakYaak said:
.
I've seen on this forum multiple times that if you are using 90C rated wire at its 90C amperage rating (e.g. #12 THHN for 30A), and you want to upsize the conductor in order to terminate it in 75C terminals (in this case, from #12 to #10), you need to make those splices using 90C connectors "in a separate, otherwise empty enclosure".?
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A few things no one has mentioned:

1. Note that due to the "small conductor rule", 240.4(D), you cannot protect #12 @ 30 amps for most general applications.

2. The code does not state a distance or that the transition to the other conductor must must be in a separate enclosure. Some apply the setup found under the UL testing procedure for circuit breakers, but again it is not in the NEC.
 
electrofelon said:
1. Note that due to the "small conductor rule", 240.4(D), you cannot protect #12 @ 30 amps for most general applications.
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In my case, the circuit is being used for an air conditioner. MCA is 23A, and there will be 6 current carrying conductors in the conduit. My calculation was that I'd need to start at 30A capacity in order to still have at least 23 after adjusting to 80%. (30 x .8 = 24)
I'm not concerned about the small conductor rule rule, bc of the air conditioning/refrigeration exception in 240.4(G)
 
YaakYaak said:
In my case, the circuit is being used for an air conditioner. MCA is 23A, and there will be 6 current carrying conductors in the conduit. My calculation was that I'd need to start at 30A capacity in order to still have at least 23 after adjusting to 80%. (30 x .8 = 24)
I'm not concerned about the small conductor rule rule, bc of the air conditioning/refrigeration exception in 240.4(G)
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Yep certainly you are good if it's AC 🪭
 
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