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.
#119686 - 01/16/0510:59 AMRe: The Joys of a Maine Winter and Conduits
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.
#119688 - 01/16/0502:37 PMRe: The Joys of a Maine Winter and Conduits
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?
Mark Heller "Well - I oughta....." -Jackie Gleason
#119689 - 01/16/0504:19 PMRe: The Joys of a Maine Winter and Conduits
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.
#119690 - 01/16/0504:53 PMRe: The Joys of a Maine Winter and Conduits
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!
#119692 - 01/16/0506:08 PMRe: The Joys of a Maine Winter and Conduits
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.
#119693 - 01/16/0508:24 PMRe: The Joys of a Maine Winter and Conduits