When I had the piping of my house redone, they left most of the old pipe for cold water in the wall. This is a 18mm steel pipe which runs vertically through (almost) three storeys.

Currently, I am redoing the top storey and strongly believe it is a good idea to have electricity, ethernet and TV up there. Laying cables inside the wall is tedious and now I'm looking at this old unused pipe, which could fit a couple of cables easily.

However, I have sort of a bad feeling at the idea of putting a 230V AC power cable inside a (roughly) 5m long straight steel pipe. School was a long time ago, but I still think I would be building a quite formidable electromagnet, wouldn't I?

In this case I think it would be better to ground (add ground to?) the pipe, put only ethernet and TV inside the pipe and have the power cable outside of the pipe.

How correct or incorrect am I with my assessments? Is it at all wise to use a steel pipe to house any sort of cables?

  • 1- Running a power cable inside a steel pipe does not make an effective electromagnet so don't worry about that. 2- Have you looked at the inside of the pipe? Is it not corroded to death - making the inside surface very rough and likely to damage the insulation on any cable you try to pull through it? – brhans Aug 15 '16 at 19:17
  • @brhans: For its 40 years the pipe is in a very good shape ... according to the plumber who took a close look at a piece of the part they took out. I still was going to pull a bit of steel wool up and down a few times before the actual cable. I will only pull one cable through with a diameter of 11mm (outside) so I hope it will not scratch against the pipe that much in any case. – user1129682 Aug 15 '16 at 20:01
  • Can you just run your electric cables in the wall next to the pipe? Perhaps you could access the same cavity but avoid the risks and confusion that go with trying to run power through a water pipe. – Shimon Rura Aug 15 '16 at 20:10
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    Could you remove the water pipe and replace it with plastic conduit of a close outside diameter? Maybe not depending on how it's attached inside the wall, but if you could use the old pipe to guide the conduit as you pull it out it might work – Drew Aug 15 '16 at 21:52
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    FWIW, if you could fit a PVC or similar pipe with smaller diameter into your steel pipe (and can verify that it hasn't got damaged by pulling it out, and re-inserting it), I'd say it'd be 99% safe to use it as a conduit then. A rubber hose with a proper diameter could work too. Alternatively, remove the stell pipe and replace it with PVC one. If that's not an option - that pipe is certainly safe enough for low voltages/amperages (i.e. ethernet/TV), especially if you add some external insulation to them (e.g. put them in rubber hose themselves). Still, DON'T use the pipe for mains directly! – vaxquis Aug 15 '16 at 23:38

Wires are routinely run in steel conduit, NOT pipe. Old water pipes would be rough and may have standing seams that can cut the insulation. The electrical code in the U.S. would not allow this because the water pipe is not listed for wiring purposes. Used water pipe for a wire way is asking for problems. Added: I currently work in a lumber mill. A few months ago the owner bought almost 1k' of used conduit big stuff. We cut off most of the rusty threads and tossed the rusted conduit. To make a tough week+ of pulling 500kcm 3 phase we had a short in the pipe on the first pull then 2 on the second . This was only ~200' after the 2nd pull and close to 600' of 500 being damaged. We now don't use rusty conduit. This has happened in just the last few years with used conduit. Water pipe is much worse.

  • Hm, is that stuff that tough? I thought a bit of steel wool can take care of that problem. I have a left over brand new stainless steel pipe with a smaller diameter, I think. If I can put the stainless steel pipe inside the old pipe and run the cable through the inner stainless steel pipe, I can eliminate that problem. Still probably outside of any applicable regulation, but safer. I was wondering what I should do with the leftover pipe. – user1129682 Aug 15 '16 at 20:05
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    Steel wool isn't going to do much. It might clean out some of the dirt but it's not like you're sandblasting everything smooth. Could this work? Sure. Is it a good idea? No. – Shimon Rura Aug 15 '16 at 20:21
  • Can you run a conduit inside the pipe? That might be the best approach here if you don't need to run that much wiring -- ENT aka "smurf tube" would work well here as a protective inner-layer for the pipe, if you can get an equivalent product where you're at... – ThreePhaseEel Aug 16 '16 at 2:05
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    As for structured cabling, it is unlikely that the pipe corner radius would be wide enough to allow the cables to turn comfortably. There is nothing as frustrating as an Ethernet link that is intermittently working. – Aron Aug 16 '16 at 2:15
  • @Aron -- this could very well be a straight pipe (where corner radius isn't a concern), and ENT or equivalents can be used for mains branch circuits (at least over here). – ThreePhaseEel Aug 16 '16 at 3:30

Running wires or non-metallic sheathed cables down the inside of a rough pipe (vs. a smooth-walled conduit) is inadvisable for the snagging/shorting reasons Ed Beal already mentioned in his answer; however, there are a couple of options available -- a flexible conduit (FMC/"greenfield", ENT/"smurf tube") can be run down the pipe and the mains wires can be run through it, or a metal-clad/armored cable (AC/BX, MC(I-A)) can be run through it without fear of damage. Either way, using it directly as a chase for the Ethernet and TV cabling is fine provided there aren't bends in the way -- insulation damage isn't a major concern for the low voltage cables, but neither Cat5/6 UTP nor coax (nor AC/MC, FMC, or ENT, either) tolerates pipe-elbow-radius bends well at all.

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