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essacm

Member
Location
meriden ct
Occupation
electrical contractor
I recently installed pvc outside and an inspector is requiring I use an expansion coupling is this accurate I looked up the code article and found the average temp difference in my city which is a high of 80 and a low of 40 would I then do the math off the difference he thinks its off of how hot and how cold a place can get which I think is inaccurate thoughts ?
 
So with a 40°F difference in temperature the length change would be 1.62" per 100 feet. A 15' run would have a length change of 0.243" so a bit over 15' will require an expansion fitting. In my area we can easily have 120 degrees of temperature differential so a bit over 5' requires an expansion fitting.

In my opinion it is based on the average lowest and highest temperature over a year to determine the change in length. While there isn't an adder for direct sun exposure, there probably should be.
 
essacm said:
It’s for a overhead service it’s 15’ up hits a 90 and then less than 3’ to a weather head
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According to Don's calculation at 15' with less than 1/4" of expansion an expansion fitting is not required.
 
essacm said:
This is what is in question
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So the real question is what temperature change are you required to use in the calculation. You're permitted to have up to 1/4" of raceway expansion without requiring an expansion fitting. If the inspector agrees with you using 40°C as the temperature change than with only 15' of raceway no expansion fitting is required.
 
essacm said:
I recently installed pvc outside and an inspector is requiring I use an expansion coupling is this accurate I looked up the code article and found the average temp difference in my city which is a high of 80 and a low of 40 would I then do the math off the difference he thinks its off of how hot and how cold a place can get which I think is inaccurate thoughts ?
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You are in Connecticut and your low is 40 degrees? I am in Florida, it was 32 degrees here yesterday. Low 30 high 98 that is 68 degrees. That is 2.84 inches per 100 feet. That is .25/.0284=8.8 feet before I have to put an expansion fitting. The first time i did this math I was surprised because I hadn't seen an expansion fitting, ever. It is one of the things I made sure to teach in 2nd year apprenticeship. Since both of my current county inspectors are former students, I am guessing they enforce this in my area.
 
retirede said:
It looks like he is using “average” high and low temps, which is not what should be used in the case, IMO.
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Does this code section actually say how you find the temperature? Here in NJ at a CEU seminar they told us 60° F. No one really knows is my suspicion.
 
infinity said:
Does this code section actually say how you find the temperature? Here in NJ at a CEU seminar they told us 60° F. No one really knows is my suspicion.
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I don’t think it does, but at some point, common sense has to play. How could you not consider the entire range the installation will be exposed to?
 
retirede said:
I don’t think it does, but at some point, common sense has to play. How could you not consider the entire range the installation will be exposed to?
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I have no idea. This section is so poorly written it can be interpreted 5 different ways. Why doesn't it simply say the range is from the historical low to the historical high or a derated value to allow for temperature diversity?
 
infinity said:
I have no idea. This section is so poorly written it can be interpreted 5 different ways. Why doesn't it simply say the range is from the historical low to the historical high or a derated value to allow for temperature diversity?
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Maybe it needs an Informational Note like the one found in 310.15(B)(2)

Informational Note:
The ASHRAE Handbook — Fundamentals is one source for the ambient temperatures in various locations.
 
I also suspect the movement numbers using the calculation equation they give you. Has anyone ever confirmed this movement, especially with modern PVC? I have a run of about 40 feet outside and put an expansion fitting on it. I marked it with a sharpie in the summer. In the winter, it looks like that mark moved about 1/4 inch at most. 40+ degree difference and it does not move much.
 
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