110.14C spinoff question

[dicklaxt]

I was trying to explain 110.14C to a friend and he came up with the question below.I did not have an answer,so,,,,,,,,

Question

If we are going to be limited in cable selection by the temp rating of 75 degree C of the termination,why do we even have 90 degree C column in Table 310.16?The fact that this column can be used for adjustment factors certainly is not the only reason.

dick

 

[iwire]

Here is a sketch I did, turns out Square D has one almost the same.

I should note that the junction boxes would have to be rated for at least 90 C as well.

 

[hardworkingstiff]

Not only does 110.14(C) limit us to 75c, it also commands we use only table 310.16 for ampacities @75c.

 

[iwire]

Not only does 110.14(C) limit us to 75c, it also commands we use only table 310.16 for ampacities @75c.

Only if the terminals are 75C, if I have had 90C or higher terminals I can use the 90 c rating.

 

[hardworkingstiff]

Only if the terminals are 75C, if I have had 90C or higher terminals I can use the 90 c rating.

Practically, how often do you see terminals on both ends of a circuit rated 90C? My main point though was the restriction to table 310.16.

 

[dicklaxt]

Thanks guys that clears it up,,,
dick

 

[Dennis Alwon]

Lou I think Bob's point is that you can use a short piece of a 75C wire at the ends and still use a smaller 90C wire in between. Since the 90C wire is smaller it would cost less so on a long run it may be beneficial to do this. I have never seen it done and adding 2 splices would also cost more time and labor so in most cases this may not be beneficial.

Are splice terminations and JB's normally 90C rated? Never noted it myself.

 

[iwire]

Practically, how often do you see terminals on both ends of a circuit rated 90C? My main point though was the restriction to table 310.16.

110.14(C)(1) Equipment Provisions. The determination of termination
provisions of equipment shall be based on
110.14(C)(1)(a) or (C)(1)(b). Unless the equipment is listed
and marked otherwise, conductor ampacities used in determining
equipment termination provisions shall be based on
Table 310.16 as appropriately modified by 310.15(B)(6).

Dick was asking when we could use the 90 c column, there are times we can because there is equipment listed
and marked otherwise.

We can also use the other ampacity tables if the equipment is listed and marked otherwise.

Many wire connectors are listed and marked otherwise, wire nuts are one example, compression connectors are another.

The real problem I see with using the higher temp ratings is the smaller conductors will lead to more voltage drop ..... and wasted power.

 

[iwire]

Are splice terminations and JB's normally 90C rated? Never noted it myself.

I think metal enclosures are all set, I think PVC enclsures would be an issue.

I think Idea wire nuts are all rated 105 C but I am not sure.

 

[lefty]

Derating

Derating

90C wire will let you derate for multiple runs in a conduit, to a point.

 

[lakee911]

Here's a stupid question ... what does that temperature rating even really mean? Does it mean that it will get 194 degrees F (90 degrees C) under normal operating conditions? Ouch!

 

[dicklaxt]

I understand that to mean the temp that the insulation will safely endure under those parameters,,,,,,,,,some body holler if thats wrong.

dick

 

[Awg-Dawg]

I think Idea wire nuts are all rated 105 C but I am not sure.

They are.

Kinda weird, the only reason I know is I opened a bag today and remembered Smart $ mentioning this same application awhile back.

 

[ZZDoug]

the junction boxes would have to be rated for at least 90 C as well.

As I have always understood it, its not only the junction boxes, but everything in the entire enclosure. This is an important distinction lots of people either dont know or forget.