On Nov 14, 1:59*pm, David Nebenzahl wrote:
On 11/14/2009 12:07 PM RBM spake thus:





"David Nebenzahl" wrote in message
s.com...

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.)

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

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

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

--
Who needs a junta or a dictatorship when you have a Congress
blowing Wall Street, using the media as a condom?

- harvested from Usenet

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