Conduit drains?
Conduit drains?
(OP)
As is often the case, we had a little problem and I got asked a question.
We had a low voltage circuit catch fire and burn at one of my sites. The wiring in question was in conduit, installed in a Class I Div. I area and was contained except for some smoke which unfortunately triggered smoke and flame detection and killed some equipment. Naturally management got excited.
Upon opening the conduit in question, they found evidence of some rather small amount of water in the conduit. Normally these conduit systems have drains and vents installed.
The management question is: "Are we supposed to be inspecting these drains?" I've been around this stuff for thirty years and never have had that question asked of me. My quick answer is "Nobody does that."
So, do any of you have programs to periodically inspect drains on conduit installations?
We had a low voltage circuit catch fire and burn at one of my sites. The wiring in question was in conduit, installed in a Class I Div. I area and was contained except for some smoke which unfortunately triggered smoke and flame detection and killed some equipment. Naturally management got excited.
Upon opening the conduit in question, they found evidence of some rather small amount of water in the conduit. Normally these conduit systems have drains and vents installed.
The management question is: "Are we supposed to be inspecting these drains?" I've been around this stuff for thirty years and never have had that question asked of me. My quick answer is "Nobody does that."
So, do any of you have programs to periodically inspect drains on conduit installations?
old field guy






RE: Conduit drains?
Seriously, good question and I agree with your first response - no one does it. In the refinery and the aluminum plants I worked at we never inspected the drains unless there was some reason or evidence to do so. Except for causing rust on the equipment, there was not a big perceived hazard if the drains did not work. I guess if the drain is to remove accumulated hydrocarbons it would be a hazard to have gasoline in the conduit.
RE: Conduit drains?
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Conduit drains?
Are you channeling my boss or what?
He saw the pictures and knew immediately that we should Do Something. He's a mechanical engineer. He lives and dies for PM's and such on large reciprocating engines and gas turbines.
That water differential relay, though, I'm thinking that would be just the thing. Let's see... My congressman can talk to OSHA, making the relays mandatory, and I could get rich.
My controls techs don't have time to pick up another task walking around inspecting conduit drains. Maybe it's time for a contract drain inspector...
old field guy
RE: Conduit drains?
Waross,
You drill small holes in buried conduit? If there is ground water it's an invitation for water to get in, low point or not. We slope them to a vault or pullbox if they are site conduit. I have never seen anything but a fully sealed conduit system in a Class I, Div I area.
Regards,
EEJaime
RE: Conduit drains?
RE: Conduit drains?
The drains look like a pipe plug with a hole in the middle and have bug screens and other features.
Typical use is at the bottom of long vertical runs to prevent condensation build up. Or they are used on NEMA 7 motor starters and control panels to prevent condensation.
I don't know how you would inspect them except by removing them, blowing them out and then putting them back wrench tight.
RE: Conduit drains?
And to follow up my original post, I got a phone call on the way home. Apparently the investigation at the site uncovered that a fire was started by grease and oil under the engine base when a spark plug blew out and dropped hot debris. The resulting fire set off the building flame detectors, shutting down several thousand horsepower of reciprocating engines. The fire also roasted this poor little conduit and melted the insulation off the wires inside.
Had those incidents not taken place, nobody would have ever known about the 100 cc's of water inside one fitting and everybody would have been sleeping peacefully.
old field guy
RE: Conduit drains?
Conduit couplings have straight threads and do not provide a seal that will keep water out. If you install conduit vertically in a wet location, it will fill with water. The water runs down the conduit and sits on top of the coupling and works it way around the threads and over time will fill the conduit unless there is some provision to permit the water to drain out.
I too have never heard of the drains being checked, but have seen conductors damaged when the water in the conduit froze and damaged the insulation. In one case, a 3/4" conduit was split and the #14 wire pushed out the split. When the water was frozen the circuit worked, but went it warmed up the ice melted and the conduit closed tight on the conductor causing a short and blowing the control fuse.
RE: Conduit drains?
I have done many underground conduit and duct runs where the specs called for tees to be installed at the low point and turned down. In some instances a rock pit was dug beneath the tees, in some instances no pit was used. It depended on the ground conditions and the designers personal preferences.
The last time I did it, we had about 1000 feet from the sub station to the risers up the poles where the connection to the overhead distribution lines was made. The profile of the conduits was such that over 500 feet was at a higher elevation than the weatherheads up the poles. We felt that any amount of water entering the conduits would eventually exit through the weatherheads. This may not be an electrical problem but would certainly be an aesthetic issue. Add to that the possibility of freeze up and splitting. This issue was identified after the conduits were installed. The conduits were 5 inch sched 40 PVC. A worker was sent to the lowest locations with a 1/2 inch drill. We had 1/2 inch holes drilled through the conduits from the top down and out the bottom. There have been no problems related to water.
In regards to the ice issues;
Water and glass share an interesting property:
Both impure water and molten glass are conductors.
Both are insulators in the solid phase.
Water has a very high capacitive constant, ice has a very low capacitive constant.
An instance; in lumber mills, lumber with a high moisture content will appear to be dry when frozen. This will happen with either a resistance type moisture meter or a capacitive type moisture meter.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Conduit drains?
Steve
RE: Conduit drains?
Properly installed modern RGS systems are very well resistant to moisture. There is always minor amounts either from condensation or entrainment that occurs, but we are not talking about flowing water quantities. Be that as it may, would you build in fittings with unsealed openings to the atmosphere? Such as occurs with drain fittings?
SteveWag
Can you pressurize a conduit section with drain seals installed in it?
RE: Conduit drains?
I think you will find that the opposite is true. About 20 years ago the conduit couplings used in Canada had tapered threads, but under pressure from the manufacturers they changed the rules to permit the use of straight thread couplings. The conduit threads in both countries are tapered.
PS, I am in Illinois.
RE: Conduit drains?
I don't agree. Even when properly installed, vertical conduit will fill up with water via leakage at the couplings unless some type of drain is provided. The use of straight thread couplings with tapered thread conduit does not provide a watertight seal.
In non-classified areas, it is very common to find a small hole drilled in a conduit body at the low point in the run. In classified areas, drains listed for the purpose would be used. I have even seen the holes drilled in the conduit itself for underground, as Bill said in his post.
RE: Conduit drains?
You can really get conduit to hold 6 PSI?
RE: Conduit drains?
Take your boss to some water filled manholes with 25 kV cables in them!
Rafiq Bulsara
http://www.srengineersct.com
RE: Conduit drains?
I thought about that. It would scare him to death. Fortunately our water-filled manholes are not within his area of responsibility. Not only are they water-filled, but being next to a salt-water ship channel, I'm pretty sure that it's salt water in the manholes.
Let's see: We could put in a filtration and desalinization unit to process the manhole water. that's what I need...
old field guy
RE: Conduit drains?
Just a suggestion,
Regards,
EEJaime
RE: Conduit drains?
When are you guys going to learn?
Armoured cable is the way to go!
RE: Conduit drains?
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Conduit drains?
RE: Conduit drains?
Seriously, though, we're talking about a couple of spoonfuls of water in a conduit fitting that has no splices inside. I didn't get excited about the water, but my non-electrical boss did.
Roy--
If this was a box, I'd have installed a vent at the top and a drain at the bottom, both rated for Class I Div I. And i make sure that conduit never enters the top of a box unless it's completely unavoidable. No use in having whatever condensate in the conduit dripping down into the middle of the box. Side and bottom entries mitigate that.
old field guy
RE: Conduit drains?
Merry Christmas and a Happy New Year!
EEJaime
SoCal,USA