PVC Conduit

Status
Not open for further replies.
A finer point for consideration (read: potential for error :eek:hmy:).

The description beside current temperature says conduit must also be at this temperature. That is not technically accurate with the calculation I used for the amount to expand fitting at installation. That amount actually includes compensation for the temperature adder for sunlit [and rooftop] locations. So the conduit temperature essentially has to be the current temperature plus the adder.

It may present a problem if, for instance, you use the distance as calculated on a cloudy day. Can anyone suggest a solution? I considered removing the adder from the calculation but then you'd have to keep the conduit shaded on a bright sunlit day...???
 
Last edited:
Most of the time a single expansion fitting is all you need. It is when you have a long run when it can get more complex to do it right. One fitting only a foot in length in a 1000 foot run will not be able to make up an expected three foot change of raceway length.

Expected temperature change is the most important factor, if temperature is expected to remain constant your raceway will not change length. Other places you may easily expect 140 or 150 degrees F of temp change to be possible, which would need an expansion fitting on even as little as 3 feet of raceway.
 
For short runs that need some provision for expansion you may be able to get enough motion from allowing right angle segments at either end to flex and move sideways.

Tapatalk!
 
Smart $ said:
A finer point for consideration (read: potential for error :eek:hmy:).
Click to expand...
Found an error and fixed... but I did resort to simple calculation with no consideration for current weather conditions other than temperature.

The Excel file link above goes to the latest revision.

It was easier to just create another Google Sheets conversion. Here's the link for the revised file:
https://docs.google.com/spreadsheets/d/1beGaiq95WcskXYCkT3drQrH_OyRKa3nIW3aCjpxKBkw/edit?usp=sharing
 
Smart $ said:
Evaluated using the record max and min temps for TN (113, -32, swing 145) and an expansion fitting would be required for any straight run over 4.25'. That is, 1/4" change every 4.25'. :?

Perhaps I calculated that wrong... :blink:
Click to expand...
.25" expansion on a 51" pipe installed at -32F then taken to 113F ??? not quite .25"
PVC is 28^10-6 linear coefficient

on 51" of pipe that would stretch to ~51.207" from -32F to 113F.

on 40ft (480in) it would stretch to 481.9488in if installed at -32F and taken to 113F
installed at 40F that 480in with stretch ? 0.9744in
 
Last edited:
FionaZuppa said:
.25" expansion on a 51" pipe installed at -32F then taken to 113F ??? not quite .25"
PVC is 28^10-6 linear coefficient

on 51" of pipe that would stretch to ~51.207" from -32F to 113F.

on 40ft (480in) it would stretch to 481.9488in if installed at -32F and taken to 113F
installed at 40F that 480in with stretch ? 0.9744in
Click to expand...
Your coefficient is in error. It's 3.38 ? 10^-5 in/in/?F... converted for feet: 3.38 ? 10^-5 ft/ft/?F.
 
The Terminator said:
I'd appreciate any feedback you have on the not in the market below photo of a expansion deflection fitting for PVC conduit.
Click to expand...
Looks like a boot for a CV joint.

I suspect if it were on the market, very few would be purchased over regular expansion fittings just based on price point alone.

Rated for direct burial?
 
Smart $ said:
Rated for direct burial?
Click to expand...
+1
Potential advantage would be water/weather tight without sliding seals or o-rings.
Also ability to handle misalignment, but any better than a simple section of LFNC? And is misalignment a big problem?
Subject to physical damage?
UV resistant? Oil resistant?


Tapatalk!
 
Last edited:
GoldDigger said:
+1
Potential advantage would be water/weather tight without sliding seals or o-rings.
Also ability to handle misalignment, but any better than a simple section of LFNC? And is misalignment a big problem?
Subject to physical damage?
UV resistant? Oil resistant?


Tapatalk!
Click to expand...

All great questions. I sent them to the person involved in gauging the market for this potential new product. I was able to see one and felt it was worth sharing a photo with my friends at Mike Holt's forum.
 
From the 2011 NEC

352.44 Expansion Fittings. Expansion fittings for PVC
conduit shall be provided to compensate for thermal expansion
and contraction where the length change, in accordance
with Table 352.44, is expected to be 6 mm (1?4 in.) or greater in
a straight run between securely mounted items such as boxes,
cabinets, elbows, or other conduit terminations.
Click to expand...

Table 352.44 Expansion Characteristics of PVC Rigid Nonmetallic Conduit Coefficient of
Thermal Expansion = 6.084? 10?5 mm/mm/?C (3.38 ? 10?5 in./in./?F)
Click to expand...

So even if the table is wrong, it is what we have to use.
 
Status
Not open for further replies.
Top