PVC electrical conduit vs. PVC for plumbing

Question

What's the difference between PVC electrical conduit vs. PVC plumbing? Can they be used interchangeably?

Answer 1

Plumbing PVC and Electrical Conduit PVC are manufactured and tested for different applications. They are both "PVC", but additives adapt them for higher temperature & pressure ratings for plumbing use, and provide UV hardness for electrical use:

• PVC pipes are pressure tested and PVC conduit isn’t
• The wall of plumbing PVC pipe is typically thicker than the wall of PVC conduit.
• PVC is tested and rated for UV exposure, which means that it is suitable for outdoor waterproofing applications in which electrical cables need to be run across rooftops or up the sides of buildings

In terms of colour: Grey schedule 80 is a plumbing pipe, similar to the white Schedule 40 PVC piping. Schedule 80 pipes should not be used as an electrical conduit.

More:

https://www.commercial-industrial-supply.com/resource-center/difference-between-plumbing-pvc-and-electrical-pvc/

Answer 2

Actually, it's about fire

The people who write the Code want you to have enough time to escape your house before you are incapacitated by toxic fumes. "Smoke inhalation", meaning incapacitation by toxic fumes, is the #1 cause of death in fires. You are doing your best to tell your legs to "get me out of here" but your legs are all missing the timing and going sideways and falling down, because those nerve signals are being disrupted by chemicals in the smoke. You try to get back up, but your control of muscles is just getting worse and worse. You crawl a few more feet, your body is found there, and is written off as "smoke inhalation".

Plastics make this much, much worse because of the particular fumes emitted when plastics burn. This, plus the fact that they're literally made of petroleum, have dramatically shortened escape times from 17 minutes to 3.

Thanks, plastics!

So. Fire is burning, clock is ticking, what's up with PVC pipe?

With PVC water pipe, we get a mulligan because it's full of pressurized water (or vanishingly unlikely to be an ignition source, in the case of PVC sewer pipe). However, with PVC electrical pipe, good chance the source of the fire is inside the pipe.

Now let's talk about what fire is

because there's a lot of false propaganda out there. They say solid PVC doesn't burn, but by that same measure neither does liquid diesel fuel ... or solid wood! So what's burning here? The orange juice???

Full credit to Thanks to the Tribune-Star, sorry but their news page here wouldn't load the image for some reason, so I had to borrow it from Google Images.

What's actually happening here is a bit of a conceit. Diesel and PVC, and wood actually, will emit vapors when exposed to heat - and the vapors burn. These vapors burning emit more heat which releases more vapors and we have the vicious cycle that reduced this truck to ash from nothing but the diesel.

So you can call diesel and PVC "non-flammable" if you really want to.

In a house fire, it'll be an overlay of several materials burning - the wire arcing that started the show, the PVC pipe, the wood in the immediate area. Since "declaring them non-flammable" is poppycock, we really want to know "Does it burn?" The word for this is exothermic. Exothermic means if you expose them to heat + oxygen, will you get more heat than you started with? Obviously not with fire brick - all you'll get is a hot brick. But wood, definitely - we know that. Well, petroleum is one of the most exothermic materials known - that's why we use it for fuel. PVC is made of petroleum.

So in a fire, PVC will make things worse.

How do we manage/contain that?

By adding anti-fire additives to slow it down. Right off the bat, the chlorine inherently in PVC (the "C") helps. (also, makes for "interesting" combustion products).

PVC electrical conduits add further fire retardants to increase its ability to resist ignition from wires, and contain it long enough for the breaker to hopefully trip.

This field experiment doesn't contain any PVC pipe, but it does contain a PVC electrical junction box. What happens at 13:00 is amazing, no sign remains of the box at the end.

The view of the PVC industry is very firmly that PVC does not burn or emit toxins any worse than other common building materials. But what I take away from the links above is: "that's a really low bar."

Metal is better in every way

Clearly from the last video, if you think spray foam is the bee's knees, PVC conduit isn't going to make anything worse. But honestly, if I can make my house have 17 minutes to conflagration instead of 3 minutes, I'll take that, thanks.

And here's where I make the case for metal conduit. Last time I priced conduits, EMT was comparable to Schedule 40 - astonishing but true. Yet it's tougher than Schedule 80 and is superior for all purposes except burial.

As far as containing fires, obviously steel is incapable of burning nor accelerating a fire, and it definitely won't emit toxic smoke. Being grounded, it has a unique ability to deal with arc fires - it can shunt them to ground and trip the breaker! With individual wire (THHN) work, EMT serves as the ground, which saves wire and money. (it might actually be the cheapest option, surprise!)

But for novices, its best feature is everything is reusable - nothing is glued and it comes apart like an Erector Set. So there's never a worry of wasting material. You're free to "try stuff" and ask for feedback and make adjustments - you might waste a little pipe at most. (works best with compression fittings, so you don't have little setscrew dimples).

I realize the appeal of PVC is that people are familiar with it from plumbing projects, and they think metal conduit will be horrible the way metal plumbing pipe is. It's really not. Also I find PVC kit to be needlessly costly - no reason plastic boxes should cost that much. And expansion joints, no need for those in EMT.