Gray vs White PVC

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FionaZuppa

Senior Member
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AZ
quick Q, why is the gray sch40 direct burial "electrical" PVC pipe about 40% less $$ than white "plumbing" sch40 PVC? any reason why the gray PVC cant carry pressurized water (residential for backyard water)...?
 

GoldDigger

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Location
Placerville, CA, USA
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quick Q, why is the gray sch40 direct burial "electrical" PVC pipe about 40% less $$ than white "plumbing" sch40 PVC? any reason why the gray PVC cant carry pressurized water (residential for backyard water)...?

If the gray PVC is also Schedule 40 (and for some purposes the NEC requires that) then it could also withstand the pressure and temperature needs for domestic water, both hot and cold.
There may be an issue with the adhesive used. Electrical PVC joints can be made using only the adhesive, without using primer first, but pipe joints subject to high internal pressure (more than just a few PSI) requires the use of primer or a combined primer/adhesive product.

There might also be an issue with the chemical composition of the electrical PVC for domestic water use.

Around here Sch40 electrical PVC costs more than the Sch40 white stuff. But you can also get Category 200 white PVC which is thinner and cannot be used for pressurized water either.
 

iwire

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Location
Massachusetts
I would be willing to bet that plumbing codes require plumbing pipe be used not electrical conduit.

Beyond that there is no reason to assume that the PVC used for each is identical. Conduit is not designed with pressure in mind nor potable water nor heat.

IMO 'schedule' 20, 40, 80 etc only indicates a wall thickness not a strength or pressure rating.
 

GoldDigger

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Location
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IMO 'schedule' 20, 40, 80 etc only indicates a wall thickness not a strength or pressure rating.

YO is correct. :) The wall thickness of Sch40 steel pipe and Sch40 PVC pipe is identical for a given pipe size but the pressure limit is very different.
That said, for any given range of sizes and for a specific material you can associate a maximum pressure with Sch40, Sch80, etc.

BTW, in my earlier post I mentioned Category 200. That should have been Class 200 FWIW.
 

FionaZuppa

Senior Member
Location
AZ
i thought the glues were different for PVC vs CPVC ??

gray or white "PVC" should use same primers / glues ??

this Q has been posted a zillion times online, seems like the responses are 50/50 to use it or to discount its use for water.
for me its just cold water to some spigots and a outdoor sink, underground piping.
 

480sparky

Senior Member
Location
Iowegia
The larger [1-1/4 and up] white pipes used by plumbers are not designed for water pressure. They're for drain & venting only. If you look at the cut end, you'll see what is meant by "cellular core".
 

GoldDigger

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Retired PV System Designer
gray or white "PVC" should use same primers / glues ??
Yes, but the instructions for using them and for using or not using primer is different depending on the application pressure.

Also, just FWIW, if you ever wondered why air pressure testing is prohibited, it is because the solvent is flammable and the higher oxygen pressure could cause an explosion in the pipe.
 
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iwire

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Location
Massachusetts
The larger [1-1/4 and up] white pipes used by plumbers are not designed for water pressure. They're for drain & venting only. If you look at the cut end, you'll see what is meant by "cellular core".

We don't have that out here, I ran new 4" white PVC sanitary lines in my home and the PVC walls are solid.
 

K8MHZ

Senior Member
Location
Michigan. It's a beautiful peninsula, I've looked
Occupation
Electrician
i thought the glues were different for PVC vs CPVC ??

gray or white "PVC" should use same primers / glues ??

this Q has been posted a zillion times online, seems like the responses are 50/50 to use it or to discount its use for water.
for me its just cold water to some spigots and a outdoor sink, underground piping.

Yes. A friend of mine learned that the hard way. He used PVC glue on CPVC and it leaked at just about every joint. He tore it out, got new CPVC and CPVC glue and it held perfectly water tight the first time.
 

FionaZuppa

Senior Member
Location
AZ
is this info correct

"PVC is fine to use outdoors. The pressure is also fine. Schedule 40 is good for a working pressure of 200 psi+ all the way to 1-1/2" size.
It's mandated by ASTM D1785. All PVC must meet this code.
"
 

K8MHZ

Senior Member
Location
Michigan. It's a beautiful peninsula, I've looked
Occupation
Electrician
Electrical conduit is not designed to provide a water tight seal. It is not pressure rated. The inside of the conduit has debris (plastic dust) that pipe made for water does not.

Using the correct material for the application is just the way to go here.
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
is this info correct

"PVC is fine to use outdoors. The pressure is also fine. Schedule 40 is good for a working pressure of 200 psi+ all the way to 1-1/2" size.
It's mandated by ASTM D1785. All PVC must meet this code.
"
The pressure rating may or may not be directly mandated, but it is a logical consequence of the thickness and the material.
Cellular core PVC is not the same material and so not subject to the same requirements. I suspect that it does not carry the Sch40 label either.

I would be cautious about the details of PVC outdoors. I have left a couple of pieces of white PVC out in full sunlight for a couple of years and it turned very black where the sun hit it. Maybe the decomposition is just a surface phenomenon and is protecting the plastic under it, but it does not make me confident. On the other hand vertical runs of white PVC and PVC down in the weeds for sun protection seems to be doing just fine.
 

FionaZuppa

Senior Member
Location
AZ
Yes. A friend of mine learned that the hard way. He used PVC glue on CPVC and it leaked at just about every joint. He tore it out, got new CPVC and CPVC glue and it held perfectly water tight the first time.

right. but gray and white "PVC" is PVC. hot water plumbing with "pvc" should be "CPVC".
for outdoor use, the gray PVC is UV resistant.

was just checking in the electric world what others have seen, etc.
 
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