How to fix expansion joint onto 20mm PVC conduit

[DIYknot]

I'm planning to run some 20mm PVC conduit along an external wall to supply power to an outbuilding.
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?

(I've heard of non setting conduit glue but can't seem to find any)

If it's a hassle then I'll just use metal conduit.

 

[SUNRAY]

I'm planning to run some 20mm PVC conduit along an external wall to supply power to an outbuilding.
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?

(I've heard of non setting conduit glue but can't seem to find any)

If it's a hassle then I'll just use metal conduit.

How long is the run? if 30ft/10m then steel causes more issues.
I don't expect to keep water out, but to mitigate any issues that arise.
When I have any expansion position I try to make it at a lowest point, for example slope the tube downhill towards the joint.

 

[DIYknot]

About 25 m horizontal (ish) in total with a horizontal right angle bend about half way. One leg will be on a wall with half of that covered by ivy. So I could have a couple of 10m runs.

Why do you say steel causes more issues?

 

[ericmark]

(I've heard of non setting conduit glue but can't seem to find any)

I got some in error, sorry gone now, but the couplers are also extra long, I would think petroleum jelly would likely work on the long side.

 

[DIYknot]

Yes, that's exactly what I was thinking.
In the past when I wanted a more or less waterproof but sliding fitment for another application I coated the pipe in petroleum jelly and put silicone sealant in the socket. That way the sealant stuck to the socket but not to the pipe and created a perfect tight fitting yet sliding joint.

However my question was really related to the many regulations that exists (like the almost unworkable part P regs) and I couldn't believe that in one place someone had dictated that outdoor fittings must be glued to prevent water ingress and in another place someone had dictated that a sliding expansion joint must be fitted to outdoor conduit to avoid sagging but nobody had put the two together and realised they were contradictory statements.

So I was wondering if there was some magic solution that part P adhering electricians used.

 

[EFLImpudence]

Part P of The Building Regulations:

That's it; there is no more.

 

[jj4091]

https://carlonsales.com/techinfo/installationtraining/IT-NEMAEXJTA.pdf

20mm conduit expansion joints uk - Google Search

 

[DIYknot]

Yes, I have the regs books, hence my comment about P . Section 2.5 quotes Reg 12(6A) and says that the 'installation of a new circuit' is notifiable but the definition of 'a new circuit' rather depends upon where you look and nowhere does it define "reasonable provision"

But with regards to my question, the 16th Ed regs section 4.5.1, para 3, says

"Conduit systems must be designed and erected so as to exclude moisture, dust and dirt. This means that they must be completely closed, with box lids fitted"​

yet para 8 says

"Allowance must be made, in the form of expansion loops, for the thermal expansion of long runs of metal or plastic conduit."

Expansion joints cannot be completely closed and can't exclude moisture.

 

[DIYknot]

https://carlonsales.com/techinfo/installationtraining/IT-NEMAEXJTA.pdf

20mm conduit expansion joints uk - Google Search

That's an American standard though. This work is in the peak district in the UK. We have far more jobworths over here

 

[jj4091]

That's an American standard though. This work is in the peak district in the UK. We have far more jobworths over here

It will still expand and contract the same as in the UK, it was to give you an idea of how much and how to construct the run to allow for exp/cont. The second link is the expansion joints you were looking for.

 

[SUNRAY]

Steel expands with heat, I've known long runs pull screws out. Also I'll use the word buckle but that's really too strong a work, I've seen steel look like a sine wave ie up and down between fixings without, but expansion joints always seem to rust badly and I've encountered damaged wires nore than once. I don't know wheather that's due to rough edges (possibly due to rust?) or simply the movement. Of course bear in mind copper expands too and the expansion joints take out that of the steel tube.

 

[bernardgreen]

expansion loops are a way to deal with expansion

 

[DIYknot]

True, but the coefficient of expansion for PVC is much more than for steel so it expands more for a given temperature rise.
For steel the coefficient is 12E-6 so for a 10m length changing in temperature from say 0 deg C to 40 deg C that 10m would expand by just over 4 mm if allowed to. For PVC the coefficient is 7E-5 so the same 10m length would expand by 2.4 cm, nearly 6 times as much.

 

[SUNRAY]

True, but the coefficient of expansion for PVC is much more than for steel so it expands more for a given temperature rise.
For steel the coefficient is 12E-6 so for a 10m length changing in temperature from say 0 deg C to 40 deg C that 10m would expand by just over 4 mm if allowed to. For PVC the coefficient is 7E-5 so the same 10m length would expand by 2.4 cm, nearly 6 times as much.

of nice smooth plastic Vs a rough metal tube containing shards of swarf and potentially razor sharp rusty saw cuts scraping back and forth every time the clouds cast a shadow.

 

[DIYknot]

@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'.

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.