Bet you guys in warmer climes wish you had to deal with frozen conduits . We started this job in december. About the time the concrete work was done it got cold. They kept the ground from freezing with a ground heater but that all went away with the holidays. Went there last week to pull in the cables, tugged on the pull string and no movement. Oops. The conduit was completely buried under concrete so out we first tried steaming it out but with the pull string in there it didn't work well so a welder it was.

Did you say you thawed it out with a "welder"? I quess thats what it appears to be, completeing the circuit of a welder with an underground conduit. Does the welder have a thaw setting?

That can not be good. What kind of ground continuity is left after this?

Not sure why the ground continuity of the conduit would be affected? If the continuity was affected the welder wouldn't heat up the pipe. No thaw setting although they do make dedicated pipe thawing equipment. Not sure why but older welders can handle this with no problem, newer ones burn up. We pulled the string out with ice still attached to the string so the conduit didn't get very hot. Thawing pipes in Maine like this is a very common thing. Thawing conduits like this isn't. I've only done it a couple of times in my 25 years.

Now, I should say I'm not a welder, although it would be an interesting carrer change, as it's everything in reverse from our current occupations. Essentialy controled short circuits....

However, I have looked into buying some welding equipment as it wouldn't be a bad hobby. And from what I understand, newer welding equipment is rated for certain duty cycles. Like a few minutes in certain pulsing AC/DC cycles and durations, all controled by some electronics. I would assume, if you drasticaly abused a welder like that, creating a long term dead short, the welder might not survive....

As for the conduit... A long term dead short used to melt frozen water in the conduit? I would figure any couplings on that run would be arching at the threads, and would cause some damage, if not failure.

Now don't get me wrong, I have heard about this technique before. But it does not sound right.

Now I have to think up some solution this....

Invent a heated tipped fish tape. (Could be a $ maker!)

De-icing fluid, or hot anti-freeze, and then flushing and drying the conduit afterwards.

Wait for Spring.... (Nope!)

OK here it is....

Push a steam pressure washer hose down the conduit, until it blows through!

Oh wait.. did you say you tried that?

I've used methanol before, it will clear a short section of ice. I've used hot water and steam before, both work if you can get a hose thru the pipe but we had a pull string already in there, so when we pushed the hose thru it balled the string up and got stuck. So a welder was used. We're not talking a homeowners welder here. Its an industrial job fired by a 4 cylinder gas motor. Not sure why couplings would arc, I just put it in the ground a month ago and I can assure you the couplings are wrench tight. The conduit isn't being used for AC anyway. All circuits are intrinsically safe as probes and sensors are submerged in heating oil in this case.

Even considering duty cycle many welders can handle this.

The lower the current setting the more on time you can have.

I don't imagine Walrus is setting the welder to 250 amps.

I have installed units that basically do the same thing continuously to keep process piping warm.

The real trick is trying to free up a frozen PVC raceway.

This is a little off-topic, but kind of related.

I know that on the above-ground sections of the London Underground (subway system) they adopt a similar technique to get ice off the rails before the first trains of the day in cold conditions: Dead short across the tracks at one end and apply a controlled heavy current to warm the rails enough to clear them (before traction power is connected, of course). Not that even the coldest winter in London compares with Maine!

I have heard many extol the virtues of thawing pipes this way. I have also heard of the current goint "the other way," and backfeeding into a panel and causing damage.

So, what to do? I cannot discount the hazards that might be created- remember that current takes ALL paths, not just the easiest.

I suppose that, if this was a recurring problem, I might consider oversizing the pipe, and running a length of self-regulating Raychem ice melt cable inside the pipe. This might be a way to free the wires without creating a hazard, or damaging the wire insulation.

Walrus, what part of maine are you in? I live in corinna.

John there was an article in an old trade magazine that told the story of a water company doing this to thaw their water lines and burning down a few houses in the neighbor hood.

I can not remember what the actual cause was but it turned out there was a wiring problem that did not show up until they applied some current to the water lines.

I was working in Augusta but I live in Bucksport.

Wasn't worried about back feeding anything as its a bulk plant in the middle of a field. The building you see is 7 by 20, actually built around a 4 posted steel canopy like you'd see in a gas staion. The building will be unheated and only houses a sub panel, a couple of 4 ft lights, a tank moniter and 4 5hp pumps. The loading rack ( for home heating oil trucks) is on the roof of the building. If we could have thawed the pie with steam thats how we would have done it. It was a welder or a jack hammer.

I have a friend who made a very good suplametal income thawing water pipes this way in the foothills west of Denver. Wore out one engine driven welder and bought another best suited for just that job. Otherwise, he was a professional welder by trade.

They do make a machine to do just this.... amazing thing is..... it looks JUST like a welder

e57 - Heated fish tape.. no problem, tie a wire to the head (leave plenty of lead hanging out of the pipe), tie the lead on the head to the + and the rear of the pipe to the - of the welder and viola, heated fish tape.

We don't normally have to use this method for conduits in Virginia, but I have very often used it for plumbing pipes.

Once when I worked at the Prison, we had a 2" water line going up into a tower. I was at the tower for another reason when the plumber came by to see what he could do with the water. As we are checking outside, the welder rides by, we flag him down.

No biggy, we hook up one lead up top, one lead down below. This tower was near one of our farm offices, "Hey guys, I've got coffee in here" said one particularly friendly farm guy. Figuring it will take this 2" pipe a long time to thaw, we proceed OUT of the cold into warm java.

Yeah, seeeeee, THAT'S a mistake. Yup, melted all the joints.... but the water was flowing

Good thing we had plenty of inmates looking for something to do that day. Unfortunately, you can only let them so close to the head of the tower.

Hey, how do you thaw a PVC pipe?????

Aw, c'mon George...... Everybody knows you just connect it to the welder with plastic conductors!

Thawing a plastic pie with wires in it, would require waiting till spring or digging.Without wires, I'd use a wallpaper steamer and plastic tubing. Push it up the pipe, vac out the water. Slow but it works.

"Yup, melted all the joints.... "
Seen a transmitter aerial/antenna made from copper plumbing by a radio amateur. When high power was put into it, the solder melted. It seems solder has a much higher resistance than copper.

Submitted for TwinCitySparky





Thanks for sending them in, looks like a nice rig.

Bob

I'm sure I have in my collection of old books one from the earliest decades of the 20th century explaining how to thaw fire hydrants using I^2R. There is also a detailed description of how to dry out flooded xfmr and motor windings by the same method.

Of course, you do hazard the unpredictable effects of stray currents this way. Some of these same publications recommend using one's tongue to test the polarity of DC circuits, or dangling a candle at the end of a length of solid #12 to explore hollow walls...

We have learned a great deal about safety since then.

Now, the closed-loop hot water deal, that's clever. It makes me so glad I live in central Texas where I don't have to be that clever!

BTW since this OP I have purchaced a welder - a wire feed.

On the water method how do you get the water out? Swab and vaccum?

Swab & vacuum, or go get the ingersol/rand air compressor.

TwinCitySparky that is a neat idea.

You can even stay warm. Maybe a hot dog or 2 and some corn on the cobe in that pan and your all set.

Back in my hometown they would make the fire plugs glow cherry red trying to thaw water pipes for its customers. During one of the coldest winters on record they actually destroyed a lot of them trying to thaw them.

The real threat was burning the house down. If the grounds weren't properly removed/isolated and the welder could find an alternate ground path to/from the house wiring it would start fires. With no water to put out the fire alot of houses burned to the ground that year.

If you don't know what you are doing it can be very dangerous to thaw pipes with a welder.

RSlater,
RSmike

LOL!
My wife wishes that I had stuck with that plan alone.