How to fix expansion joint onto 20mm PVC conduit

[JohnW2]

I appreciate that when run externally the various conduit fittings should be glued on to prevent water getting inside the conduit (this is in the peak district so there could be a lot of water coming down from the sky!). ... However, I need an expansion joint as I have a long horizontal run. By its very nature you can't glue that on at both ends or it won't work. .... How do I make the expansion joint water tight? - Or don't people bother?

As far as I can make out,no-one seems to have commented on your last question there ("Or don'tr people bother").

If one puts an outdoor cable inside conduit, it's for aesthetic reasons and/or to protect UV-sensitive cable from sunlight (or maybe to protect from 'mechanical damage'). Otherwise, it would/could just be clipped to the wall, since no acceptable cable would care about getting wet (or even being submerged in water..

It follows that it doesn't matter a jot even if the conduit 'fills up with water' - so simple (not water-tight) 'sliding' expansion joints' would b fine'. I don't know whether any people 'bother' about the 'non-water tight' issue, but they certainly don't need to !

Kind Regards, John

 

[SUNRAY]

@SUNRAY I'm not sure what your point is. You say you've seen steel conduit pull screws out on long runs, which is understandable if the runs were very long and the screws on the fixing brackets were too tight against the conduit, so preventing it from moving. However, this is a situation that would be much worse for PVC unless you are prepared for it to sag between fixing points. Also that you've seen damaged wires, also understandable if suitable precautions such as bushes hadn't been taken at the tube ends of steel conduit.

So what are you saying? PVC is better than steel? I don't mind one way or the other except that PVC is easier to fit but needs expansion joints.

So my original question was related to how professionals manage to abide by the rule that exterior PVC conduit must be 'completely closed' with the additional rule that expansion joints 'must be fitted', when by definition expansion joints cannot be 'completely closed'.

I think you'll find the opposite is true and most provide the means for the inevitable water to escape.

If I did use steel for a short 10m run it would avoid the use of expansion joints, so enabling me to make it 'completely closed' and the small 4mm expansion between 0 and 40 deg C could easily be accommodated by a slight movement at the corner (so long as the saddles / spacer bars allowed for a little movement). However, I appreciate that it's more of a job to fit to a high standard.

@bernardgreen
Yes, that is a solution but maybe a bit OTT fo a short 10m run that will only expand by 0.4cm for steel or 2.4cm for PVC. Simpler to just have slightly loose conduit saddles / spacer bars and let it expand into free space at the end.

One job was exactly 4 lengths of steel conduit, back entry through box in the middle going through the wall to a stop end back entry box, at each end a 3 way tee, up going about 2m to a stop end box carrying a bulkhed fitting and down about 1m to a galve outdoor rotary switch. Whole thing was done in the winter with lots of snow and ice (reason they were fitted) and done with only 2 cuts and 4 threads, simple and quick job. I'll say a couple of years later, time flies and may have been 4 or 5, on a scorching hot day I was on the job to replace the lights which had changed from crystal clear to dark manky brown. The whole lot was in a horrible state with lots of internal environmental damage and the decision made to refurbish including rewire. Removing the tee box lids found the single screw through the back into a red wall plug not doing their job one screw laying in the tee box, the other had slipped down into the switch backbox, both were bent. Attempting to replace with a new screw meant drilling another hole in the brick as the existing was nowhere to be seen through the hole in the box.

Another job a long straight run of stainless steel tube with a tee every other contrete upright ~30ft/10m running up to a light. 6 or 8 of them. Every tee box fixed with a concrete screw. Most of the screws has snapped and very obvious wear as the ss boxes had been grining against the concrete and a farir few saddles missing too.

 

[Murdochcat]

Why run in conduit at all?

 

[JohnW2]

Why run in conduit at all?

Valid question but,as I wrote ...

If one puts an outdoor cable inside conduit, it's for aesthetic reasons and/or to protect UV-sensitive cable from sunlight (or maybe to protect from 'mechanical damage').