PVC conduit

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bensonelectric

bensonelectric

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Why is it that electrical PVC conduit almost never seems to keep out leaks, when plumbing PVC (Sch 40) can prove able to hold in pressures of 150+ PSI?

I only ask this because I had to dig up some conduit the other day, and when I finally got it out of the ground the whole thing was filled with water. I asked the guy who installed it, and he said he glued each joint, and even twisted the pipe a 1/4 turn after inserting according to the directions. I wouldn't be so concerned if it wasn't for the fact that I just built a pneumatic air cannon out of 2" Sch 40 PVC, and it holds a pressure of 150PSI without a problem. The only difference I could see was that I used primer, and he had not, so is primer really worth the extra effort when doing PVC conduit jobs?
 
Re: PVC conduit

I thought I remembered a post on this a while back. After doing a couple searches I found this. PVC glueing Hope it helps.
I know what you mean. Seems like you bury the pipe and if you dig it up the next week its full.

Mike
 
Re: PVC conduit

Most mfr require a primer during the glue prep process.

There are several other factors at play here.
Condensation of the pipe, but it should not be enough to fill it up.

You said he gave it a 1/4 inch turn, but there are other steps to take that are just as important as the other.


Let me run down a list of procedures from a mfr.

Was the glue stored in excess to the mfr labeling?
(If the glue sat in a toolbox or van during the summer for an extended amount of time, the temperatures would exceed that of the label. 110F is targeted.)

Was the expiration date checked? (Usually on the bottom of the can.)

Did he clean and thoroughly dry each end to be glued? (Cleaning and drying, then laying the pipe back down on the ground defeats this purpose, using a piece of cardboard or paper under the cleaned end would prevent this.)

Was the applicator more than 1/2 the size of the pipe, in diameter?

Did he apply a primer, if recommended? (Most do.)

Did he apply even layers and prevent a puddling effect of the excess?(Usually during colder temps puddling will occur.)

Did he hold the joint for atleast 30seconds before releasing? (May require longer times during colder temps, to prevent a "push out" effect.)

Did he throw it in the ditch immediately? (Handling time is around 5 minutes after gluing, where pressurized piping would be about 1/2 hour, longer times apply with lower temps.)

Edit: Sorry poolboy, I didn't see any links to that and I was already chipping away at the stone. :cool:

[ January 28, 2006, 10:20 PM: Message edited by: throttlebody ]
 
Re: PVC conduit

I have seen many electricians assemble PVC conduit with a minimum of glue, which would allow moisture to enter the conduit providing there was enough ground water. When you took your PVC out of the hole/trench, was the hole full of water? If not, what makes you think the conduit leaked?
Think condensation. Air within a conduit that is kept at a cool temperature due to burial in the earth and is then warmed by current carrying conductors.
 
Re: PVC conduit

There's also the very real possibility that the water is getting into the conduit from the above-ground ends. 100% water-proofing is not easy.

Ever have a service cable channel rain into an interior panel from the top of the meter base?
 
Re: PVC conduit

I used to use just rigid conduit at gas stations. When I switch to PVC underground, I noticed they were always filled with water when the steel conduits were not. I've had PVC that fit together so loose that I was nervous about it staying together. I've also had it where it fit so tight that I would have felt comfortable pushing it together and dropping it in the ditch with no glue.

I think a lot of it has to do with the manufacturing.
 
Re: PVC conduit

Originally posted by hardworkingstiff:
I used to use just rigid conduit at gas stations. When I switch to PVC underground, I noticed they were always filled with water when the steel conduits were not. I've had PVC that fit together so loose that I was nervous about it staying together. I've also had it where it fit so tight that I would have felt comfortable pushing it together and dropping it in the ditch with no glue.

I think a lot of it has to do with the manufacturing.
Click to expand...
I have found that Carlon gray glue sucks. I use extra-strength PVC (plumbing) glue.
 
Re: PVC conduit

Originally posted by LarryFine:

Ever have a service cable channel rain into an interior panel from the top of the meter base?
Click to expand...
HAHA! Now that you mention this, I have. I had to service a kitchen circuit in a multicircuit box for lighting and recptacles. I had a coworker shut off those circuits and was still getting a reading from my pen. He insisted it was a "phantom voltage" ( common amongst 3 wire applications). BUZZZZ! I got lit up, I was mad at him and made some remarks, went down and looked. I thought he shut off the wrong circuits, being mad at the time, I shut off the entire main. I walked upstairs and proceeded to fix the circuit and BUZZZ! Again! I pulled the covers to the panels and low and behold. Water was running into the panel at a very low rate. Just enough to connect the main to 1/2 of the bus. The sprinklers were activated outside and one had been place in front of the meter. DOH! :eek:
 
Re: PVC conduit

The fact that PVC conduit gets water in it, while regrettable, is of no real conseqence. If it's being buried, we're required to use conductors rated for a wet location anyhow.
 
Re: PVC conduit

Originally posted by bensonelectric:
I just built a pneumatic air cannon ....
Click to expand...
Cool. :cool:

Mine looks like this:

m3aphoto.gif


Does yours shoot potatoes too?
 
Re: PVC conduit

Originally posted by mdshunk:
The fact that PVC conduit gets water in it, while regrettable, is of no real conseqence. If it's being buried, we're required to use conductors rated for a wet location anyhow.
Click to expand...
Yes, you are right; and have you ever seen what happens to the wire and conduit when the water freezes?
:)
 
Re: PVC conduit

I used to use just rigid conduit at gas stations. When I switch to PVC underground, I noticed they were always filled with water when the steel conduits were not
Click to expand...
My guess is that rigid conduit is not watertight, but PVC when glued properly is. Therefore, if water were to accumulate in the rigid it would eventually drain out on its own through the couplings. Water in the PVC has no where to go.
 
Re: PVC conduit

Not a pvc expert but I did work on hydo systems for 12 years. and high pressure leaks are easier to seal than than?low pressure ones. Under pressure the pvc expands against the fitting increasing the seal. hydraulic pressure in the ground is compacting the pipe decreasing the seal. I would think that pluming pvc under the same conditions might be prone to leaks.
 
Re: PVC conduit

If pvc is glued correctly, electrical or plumbing, it will not leak no matter what the pressure is as long as you don't exceed the pressure rating of the pipe. Now if it is a vacuum (negative pressure) I don't know. Have you ever cut apart a properly made glue joint, the two pieces are literally one.
 
Re: PVC conduit

Originally posted by Paul B:
If pvc is glued correctly, electrical or plumbing, it will not leak no matter what the pressure is as long as you don't exceed the pressure rating of the pipe. Now if it is a vacuum (negative pressure) I don't know. Have you ever cut apart a properly made glue joint, the two pieces are literally one.
Click to expand...
I disagree.
As a master electrican and certified water distribution manager, I've installed and maintained a lot of piping systems. PCV water piping has a harder finish, has to be assebled with primer, and the fittings are tapered (the pipe will push back out due to the hydraulic pressure)
PVC conduit is a softer plastic and no primer is used.
Often a PVC conduit fitting can be broken by hand.
PVC conduit will always leak.
 
Re: PVC conduit

Tom, Do you mean the glue joint can be broken or the fitting? I have wasted a lot of conduit changing thing around if you can take them apart by hand.
 
Re: PVC conduit

Very little, if any, of the water entry into PVC conduits is a result of leaks at the joints. It is a result of the moisture in the air condensating out over time and filling the pipe with water. Threaded conduits do not have water tight couplings and the condensate that forms can leak out. Ground water can also leak in, but the code says that all of the conductors in underground raceways must be suitable for wet locations.
Don
 
Re: PVC conduit

Yes, you are right; and have you ever seen what happens to the wire and conduit when the water freezes?
Click to expand...
I have never seen this cause damage to the condutors when the raceway was PVC, but have seen damage when the raceway was metallic.
Don
 
Re: PVC conduit

Originally posted by don_resqcapt19:
. . the code says that all of the conductors in underground raceways must be suitable for wet locations.
Click to expand...
Don, I just had this conversation, but I couldn't find the entire concept expressed in one place. Can you please dig me up an article?
 
Re: PVC conduit

Take a look at 300.5(B) Listing. Cables and insulated conductors installed in enclosures or raceways in underground installations shall be listed for wet locations.

This is from the 2005 NEC

Chris
 
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