Making outdoor conduit watertight

[David Nebenzahl]

Did a small job yesterday making a short run of outdoor conduit watertight; homeowner gave me the connectors (elbows and compression fittings) and had me replace the existing ones.

The compression connectors were labeled "concrete tight", and when I asked him if that meant they were truly watertight, he said he was told they were by someone where he bought them (which I think was a big orange store).

So what's the recommended practice to make metal conduit watertight? Yes, I know one can use plastic, but I'm interested in how to make the steel stuff withstand weather.

I have seen wiring failures in outdoor conduit caused by the ingress of water; in one case, a nick in a wire caused by pulling it caused corrosion to the point that the wire actually broke in two.

(This installation is mostly under an eave, so watertightness isn't super-critical, but keeping water out is a Good Thing.)

[RBM]

If you're using EMT, use rain-tite fittings. If your wires are THWN, it doesn't matter if they get wet

[David Nebenzahl]

On 11/14/2009 12:07 PM RBM spake thus:

... as long as there are no breaks in the insulation.

So what's the diff betwixt raintight and "concrete tight"?

[RBM]

One is designed to keep out rain, the other concrete. Some concrete tight fittings are also rain tight, but not all.

[John Grabowski]

*Under the eave is considered a damp location, not a wet location. I don't recall seeing watertight connectors for EMT. The compression connectors are considered rain tight. Use conductors rated for wet locations and be careful not to nick them and they should be fine. Use weatherproof boxes with weatherproof covers.

When I did conduit jobs in concrete decks and such I always wrapped the connectors with duct or gaffers tape. Even if they were considered concrete tight, without the tape wrap some concrete juice would always seep in and harden in the conduit.

PVC and liquid tight conduits are waterproof with proper fittings.

[DD_BobK]

Concrete tight connectors are designed for use where emt, connectors & boxes are to embedded in concrete. Concrete, while semi-fluid when placed, is a far cry from water. Most concrete mixes (ideally) have very little excess water, so unless excessively wet or excessively vibrated, will not "bleed" a lot. Concrete forms only needed to be failrly tight, not water tight.

Concrete just cannot leak into small but visible cracks the way water can.

Rain is......well..... water but a rain condition is not the same as full continuously submerged condtion...... so rain tight is not water tight.

There are electrical enclosures (& this is getting out of my area of experience) that are for indoor use, ones for outdoor that are rated rain tight, ones for washdown, ones for industrial environment, ones that are fully submersible.

Fittings & enclosures give increasing levels of service.

Kinda like clothing for a person; dry weather clothes, rain gear (rain coat or umbrella) , wet suit, dry suit, NBC suit.

So if fittings are rated concrete tight, they're definitely fin for indoor or under an eave but I wouldnt use them exposed to the elements....I switch to the compression style that I believe are rain tight.

cheers Bob

[David Nebenzahl]

On 11/14/2009 4:06 PM DD_BobK spake thus:

The concrete-tight connectors *are* compression fittings. They look pretty watertight, but who knows? (Certainly better than the screw-tightened connectors that were there before.)

[BillGill]

Ok, I have no expertise in any of this, BUT. I figure that water can get into any place that is below grade, and a lot of places that are above grade. Trying to make something impervious to water is pretty much not possible. So I would go ahead and use quality conduit, and then use conductors that can be immersed in water, figuring that at some time they will be.

Bill

[Wayne Whitney]

Compression fittings come in various flavors, e.g. concrete tight or rain-tight. I think they may all be concrete tight, but they definitely are not all rain tight.

Cheers, Wayne

[Wayne Whitney]

I think this is the wrong emphasis. The wiring failure was caused by the nick in the wire; water in exterior conduit is a given, from rain or just from condensation.

Cheers, Wayne

[gfretwell]

225.22 Raceways on Exterior Surfaces of Buildings or Other Structures. Raceways on exteriors of buildings or other structures shall be arranged to drain and shall be raintight in wet locations.

Note they say it must be "arranged to drain", so they know you will accumulate water, no matter how careful you are. I also recommend you keep all wirenuts toward the top of the boxes and pointing up. That helps with GFCIs

[David Nebenzahl]

On 11/15/2009 9:35 AM Wayne Whitney spake thus:

So are you saying the ones I coulda/shoulda used would say "RAIN TIGHT" on the package? These ones said "CONCRETE TIGHT".

[David Nebenzahl]

On 11/15/2009 9:39 AM Wayne Whitney spake thus:

Yes. I guess the take-away here is to be extra careful fishing and bending wires in outdoor conduit so as not to nick them.

The little job I had to do revealed one stranded and one solid wire in the existing conduit. It really is a bitch to re-pull solid wire without nicking it.

[DD_BobK]

The concrete light ones that I have used were not compression style.....slip on w/ a set....concrete tight per the carton labeling.

I was actually pretty surprised that the slip on type were rated "concrete tight" but my subsequent experience with concrete showed that for something to perform "concrete tight" isn't all that hard.

cheers Bob

[DD_BobK]

Use wire lube, it really helps.

cheers Bob

[David Nebenzahl]

On 11/15/2009 10:04 PM DD_BobK spake thus:

Thanks. Next time I will.