PVC expansion Exterior

F

Fordean

Senior Member
Location
New Jersey
Occupation
Electrical Contractor
I have a job, I removed very sloppy SE cable install and changed to 150 amp inside PVC.
After I started. I questioned if I needed Expansion fittings anywhere here.
I needed to follow the Rake of the building. And not go straight across, Due to obstructions.
Looks Neat now. But I did not continue until I figure do I need 1 or 2 or none of the PVC expansions.
Doing this today. Weather held up job for a month. Attached is job with measurements
 

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You do need expansion joints.
Locally they are required on anything outside where the PVC is greater than 7 ft and between fixed points.
NJ temperature variance may call for joints on shorter runs but IMO it looks like you need three
 
Can someone provide the calculation? I've never really understood this. From an inspector CEU class we were told for NJ use 100° F to determine the expansion or contraction length. If you install this on a day when the temperature is 50°F then the maximum temperature change is 50° not 100° therefore the change in length will be 1/2 of the value if you used 100° in your calculation.
 
Fordean said:
Where would they go This confuses me so much There is not one example from manufactutes??
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Augie said any run more than 7' so that would include the two runs at the top along the peak and the run to the right where the two LB's are.
 
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infinity said:
Can someone provide the calculation? I've never really understood this. From an inspector CEU class we were told for NJ use 100° F to determine the expansion or contraction length. If you install this on a day when the temperature is 50°F then the maximum temperature change is 50° not 100° therefore the change in length will be 1/2 of the value if you used 100° in your calculation.
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Table 352.44 provides the code data. I thought there used to be an informational note referring to some govt. publication on ambient temperature, you could use, but here in Florida, you can go from 25º to 105º which is 80º. Obviously other areas are different.

80º is 3.24 in/100ft per the table or .0324 in./foot
.25"/.0324= 7.72' so 7.72 feet will expand .25" or 1/4" with 80º change in temperature.
 
augie47 said:
I think you will find everything you want to know and more here:


We use the 100 deg change here also which the chart shows an expansion of 4.1" per 100' so that works out roughly to 7 ft for a 1/4" change which is where the Code says you need to address expansion
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The part I'm not getting is that the 4.1" of expansion is only if you installed that in the coldest day that is part of your 100° spread. If you installed that on a day that was 50° more than the coldest day the maximum expansion would only be 2.05". What's not making sense to me is that the air temperature at the time of installation is not part of the formula.

Is this a classic example of me overthinking things?
 
infinity said:
The part I'm not getting is that the 4.1" of expansion is only if you installed that in the coldest day that is part of your 100° spread. If you installed that on a day that was 50° more than the coldest day the maximum expansion would only be 2.05". What's not making sense to me is that the air temperature at the time of installation is not part of the formula.
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To determine _if_ you need an expansion fitting, you only think about the temperature spread, because that determines the total motion over the complete temperature cycle. If you installed on the coldest possible day, then you have all of the possible expansion to consider. If you install on the hottest possible day then there is no possibility of expansion, but you have all of the possible contraction to consider. The total range of expansion and contraction stays the same.

Where you have to consider the temperature at installation time is where you set all of your movement compensation elements. If you install on the hottest day, then you set everything to allow for contraction, and if you install on the coldest day then you set things to allow for expansion. The Carlon document describes this starting on page 3.
 
jim dungar said:
Isn't the ambient temperature at time of installation considered when determining where to place the piston?
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According to Augie's link yes. I know people much smarter than me thought this stuff up I'm just trying to figure out the failure in my logic.
 
jim dungar said:
Isn't the ambient temperature at time of installation considered when determining where to place the piston?
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Definitely. If you are the extreme end of the temperature range (high or low) you need to set the fitting accordingly (piston all the way out or in).
If the ambient is 100 deg then as it gets colder the PVC will "shrink" so you need to set the piston "in", etc.
(its easy to get that backwards)
 
if I pull a pipe out of a cold shop then install outdoors in warm weather how long does it take that pipe to accumulate- problem long after I am done— the. What temp do I go with?…

Or the opposite- guess we have tk heat scan the pipe before install and right on each pipe- lol
 
AC\DC said:
if I pull a pipe out of a cold shop then install outdoors in warm weather how long does it take that pipe to accumulate- problem long after I am done— the. What temp do I go with?…

Or the opposite- guess we have tk heat scan the pipe before install and right on each pipe- lol
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Realistically, how often do you have a PVC run that is over 100 feet with no change in direction, exposed to outside ambient temperature? That is 7' x 16 for 4" expansion. Otherwise, close would be close enough. Let us not forget that more than likely the 1/4" per 100 feet is also conservative as the code usually is.
 
I was just stating whatever government body picks it temperature because of the ambient temperature does not mean the pipe is that so there’s gonna be a change in shrinkage or gain from the pipe to the temperature outside I was just pointing out the hypocrisy I live in such a mile climate we never use expansion points..,

I’ve been coming to the conclusion that this NEC book is like 10% safety and the rest of is garbage design issue “” not life safety
 
The temperature at the time of installation only applies to where to set the expansion joint. Lets say your your temp range is 0deg-100deg and you install at 50 deg.

So the expansion is calculated at a 100deg change in temp. You install at 50 deg which is half way of the expansion range. So if the total expansion is 1" and you install at 50 deg the joint has to move 1/2" in either direction
 
infinity said:
The part I'm not getting is that the 4.1" of expansion is only if you installed that in the coldest day that is part of your 100° spread. If you installed that on a day that was 50° more than the coldest day the maximum expansion would only be 2.05". What's not making sense to me is that the air temperature at the time of installation is not part of the formula.
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It is true that if the strategy for PVC conduit were to tightly strap it every so often, we could have a criterion like each strap can resist up to say 0.25" of expansion or contraction of the two segments on each side of it before we need any expansion fittings. Then it would be true that if you installed the conduit at the middle of the temperature range, you'd get to consider the length change of only half the temperature range, as that would be how much expansion or contraction the strap has to resist as the temperature rises or falls, respectively. While if you installed at the coldest end of the range, you'd have to consider the full temperature range for expansion only.

However, that is not the strategy that we use for strapping--the straps are supposed to let the conduit move freely underneath them from expansion and contraction. So what matters is the total change in length for the full conduit run for the full temperature range, and that is the criterion for when an expansion fitting is required. The temperature at time of installation doesn't enter into that.

Cheers, Wayne
 
Strathead said:
Realistically, how often do you have a PVC run that is over 100 feet with no change in direction, exposed to outside ambient temperature? That is 7' x 16 for 4" expansion. Otherwise, close would be close enough. Let us not forget that more than likely the 1/4" per 100 feet is also conservative as the code usually is.
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I was at a high school softball field that had a PVC run from the dugout along the top of the fence to the outfield. I don’t know what it was used for, but on a hot summer day, it looked like strand of cooked spaghetti. No expansion joints.
 
This is my possibly failed logic for the maximum permitted length of a raceway without an expansion fitting.

Example:
Two exterior enclosures with concentric KO's with a straight run of PVC in between. The length of the PVC is limited by the NEC because the expansion or contraction of the PVC over 1/4" can damage the enclosures.

100° temperature change so we'll use the maximum length of PVC without an expansion fitting of 7' as Augie stated.

7' of PVC installed when it's 0° F, expands 1/4" when 100° F. Everything good no damage to enclosures.
7' of PVC installed when it's 100° F, contracts 1/4" when 0° F. Everything good no damage to enclosures.
7' of PVC installed when it's 50° F, expands 1/8" when 100° F. Everything good no damage to enclosures.
7' of PVC installed when it's 50° F, contracts 1/8" when it's 0° F. Everything good no damage to enclosures.
14' of PVC installed when it's 50° F, expands 1/4" when 100° F. Everything good no damage to enclosures.
14' of PVC installed when it's 50° F, contracts 1/4" when it's 0° F. Everything good no damage to enclosures.
 
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