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#204154 - 11/17/11 09:16 AM Expansion Fittings in PVC  
George Little  Offline
Member
Joined: Jan 2004
Posts: 1,489
Michigan USA
This came up at a meeting of inspectors and contractors: If a environment is expected to have a change in temperature of 110° F. over the seasons and we are installing expansion fittings to compensate for this per 353.44 (2008 NEC), how do we set the fittings if we are installing conduit that has been in a warm storage area and we take it into a colder area and start installing it? For example— Warm truck or warehouse is 60° F ambient and the conduit is taken outside to a 10° ambient. Should there be a waiting time for the conduit to get tempered to the colder area? If so how long is this time? Sounds like an obvious simple answer but I don't know how to answer it. Temperature over the seasons will range from -10° F to 100° F .


George Little

2017 / 2014 NEC & Related Books and Study Guides

#204155 - 11/17/11 10:28 AM Re: Expansion Fittings in PVC [Re: George Little]  
HotLine1  Online Content


Member
Joined: Apr 2002
Posts: 6,872
Brick, NJ USA
George:
Interesting. Perhaps one should follow the installation instructions for 3/4" oak flooring. Allow the materials to acclimate to the ambient temp where it is being installed for xx hours/days.

If the install is outside, leave it lay out there for a while, and then adjust expansion joints according to install temp.



John

#204157 - 11/17/11 02:00 PM Re: Expansion Fittings in PVC [Re: George Little]  
gfretwell  Offline


Member
Joined: Jul 2004
Posts: 9,123
Estero,Fl,usa
These days a non-contact thermometer is not cost prohibitive so you could analyze the temperature of he pipe but if you cut the bundles open and start laying them out I doubt they will stay warm very long. You don't have much thermal mass there.

This sounds like a place for a controlled experiment I guess but it doesn't really get cold enough here to do it. You could get some pieces of PVC in a couple of appropriate sizes, leave it in the house/office for a day or so to be sure it is warm, then take it outside on a cold day and see how long it takes to get to the same length (temperature) as samples that were stored outside.


Greg Fretwell

#204158 - 11/17/11 02:46 PM Re: Expansion Fittings in PVC [Re: George Little]  
KJay  Offline
Member
Joined: Nov 2007
Posts: 763
MA, USA
This is what Carlon says about it. I think this seems pretty much how most of us would install them anyway.

Setting Expansion Fittings

Setting Position of Piston
If an expansion fitting was installed completely closed with
the piston bottomed on a cool day, there would be no travel
available when the conduit warmed up and expanded. If it
was installed in a maximum open position on a hot day, the
expansion fitting would pull apart when cooled. Thus, “setting”
the expansion fitting is very important.
In addition to the proper number and sizes of expansion fittings
chosen, they must also be installed so they can accommodate
the expected length change. This requires proper “setting” of
the expansion fitting. Most will be installed at a temperature
halfway between maximum and minimum; for example,
installation at 65°F with an anticipated maximum temperature
of 125°F and a minimum of 5°F. In this case, the expansion
fitting would be installed or set with the inner piston halfway
out. Expansion fittings are marked with a mid-point. If it was
a colder day, for example 35°F with the same expected
temperature change range, the inner piston would be set with
1/4 of its maximum travel out. If the temperature was hot
(95°F), it would be set with the inner piston only 3/4 way out.




#204162 - 11/17/11 03:44 PM Re: Expansion Fittings in PVC [Re: George Little]  
gfretwell  Offline


Member
Joined: Jul 2004
Posts: 9,123
Estero,Fl,usa
George's question refers to how long it will take a PVC pipe to adjust to the ambient air temperature when coming out of another environment.
I doubt you could drive very far with it in a pipe rack on the roof of the truck before it was brought down to air temperature. The problem would arise when it was stored on site and inside a heated building.


Greg Fretwell

#204164 - 11/17/11 04:42 PM Re: Expansion Fittings in PVC [Re: gfretwell]  
Vindiceptor  Offline
Member
Joined: Mar 2011
Posts: 98
San Diego
Do I have to assume that this PVC is exposed to the environment and not underground?

Other than temp power I've never allowed PVC to be used above ground.

Seen too many examples of why NOT to use it to even consider using it.


#204169 - 11/17/11 08:04 PM Re: Expansion Fittings in PVC [Re: George Little]  
gfretwell  Offline


Member
Joined: Jul 2004
Posts: 9,123
Estero,Fl,usa
I am surprised you don't see a lot of PVC in San Diego with the ocean being right there. Salt air will eat up galvanized pipe pretty fast.


Greg Fretwell

#204170 - 11/17/11 08:23 PM Re: Expansion Fittings in PVC [Re: gfretwell]  
Vindiceptor  Offline
Member
Joined: Mar 2011
Posts: 98
San Diego
Not really an issue here to speak of unless you're close to the water.

Ocal is fairly common where the environment is an issue.

I've seen and heard horror stories in the bay area though (SF) from the use of PVC, especially on roofs. Lots of fires and lawsuits over the use of PVC.

It's done, just not a common practice here from what I've seen.





#204172 - 11/17/11 09:20 PM Re: Expansion Fittings in PVC [Re: gfretwell]  
KJay  Offline
Member
Joined: Nov 2007
Posts: 763
MA, USA
Originally Posted by gfretwell
George's question refers to how long it will take a PVC pipe to adjust to the ambient air temperature when coming out of another environment.
I doubt you could drive very far with it in a pipe rack on the roof of the truck before it was brought down to air temperature. The problem would arise when it was stored on site and inside a heated building.


I can’t seem to find any official data on the subject, but based on how fast something like Schedule 40 seems to cool off on a cold winter day after I have heated it in a blanket to bend it, I can’t imagine it would take too long for PVC stored indoors at a warmer temp to acclimate to a colder outdoor ambient.



#204517 - 12/16/11 02:51 PM Re: Expansion Fittings in PVC [Re: George Little]  
mikesh  Offline
Member
Joined: Jun 2006
Posts: 613
Victoria, BC, Canada
I walked down a street in Montreal and saw many PVC services where the pipe had crumbled leaving the wires out in the open. I don't like PVC outdoors. trouble is it is cheap, easy to install and never rusts so it should be the perfect outdoor material. The Sun kills plastic and I just don't believe it lasts 40 years or more outdoors.



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