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Outside Steel Conduit Joints.
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3856 Posts
Question

We must maintain mechanical and electrical continuity of steel conduit, so can't use P.T.F.E tape or Loctite 55 at screwed joints to keep them watertight. Has anyone ever had water ingress at screwed conduit joints outside? 543.3.6.

15 Replies
broadgage
878 Posts

Are BARE COPPER CPCs still allowed ? I suspect not but am not aware of what regulation prohibits them.

It would seem to me that a BARE CPC pulled into conduit would be preferable since long runs would be earthed throughout by fortuitous contact. Joints could then be made with PTFE tape to ensure water resistance in exposed locations.

Install the galvanised conduit as normal, ensure all joints are properly tight and spray all joints with galv spray. (much easier than painting it on by hand) 

On the conduit boxes use a rubber gasket. 

mapj1
4166 Posts

The over painting of joints that are dry but gorilla tight , and in extreme locations over-taping with self-amalgamating insulation of screwed joints as well after assembly is normal in the Mil Spec world. Usually khaki or sand coloured paint though.  (If you can pick it up, walk around with it, if it moves salute it, if it is not moving then paint it…  the joke is not quite true but almost)

To be honest, with liquid sealants, if you actually do the conduit joints tight, so they really cannot be undone, rather than finger tight and rely on the goo, then the joint will almost always be electrically conductive.

Liquid conductive silver paint or even silver flake loaded epoxy is sometimes blathered about on some RF connectors. In my experience it's over-rated and nothing beats solder, or a good mechanical joint with lots of force and then encapsulated. You will also come across positive pressurized conduits in places where it really matters, where dry air or nitrogen is pushed in to drive anything else out.. 

In other cases you may ask whether it matters if the conduit is full of water - that rather depends on the cable inside it and what happens at the joints.

Mike.

Chris Pearson
3072 Posts

If in doubt, use something like Galvazinc after degreasing thoroughly. You are going to need it for running couplings in any event. Good electrical continuity will be maintained by the flanks of the threads coming together once screwed tight. It's not like a water or gas pipe where the contents are under pressure - there is nothing forcing the rain in. It might even be that surface tension helps too.

543.3.6 says nothing about being water-tight.

Tomgunn
230 Posts

I've installed 1000's of bundles of metal tubing, over the years', and never had any problems.

Why would anyone apply any PTFE??? 

The only advice I would offer is that when I fit bessa boxes, outside, I always drilled a hole, in the bottom of them, to allow any ingress to escape. IF you damage any areas, (and you shouldn't really - if you're careful), then apply some red lead paint.

 

regards…

The assumption that Locktite or tape prevents metal-metal contact is false unless the joints are not mechanically tight. The pressure between tight threads is very high, much more than is needed to break down the film or PTFE tape. This force acts hydraulically, forcing the sealant into the unloaded side of the thread, which is why they work. You may easily prove this for yourself with some plumbing and a meter, typically between a threaded item like a tap and the matching threaded socket. 

Red lead is banned now Tom, except on ships!

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3856 Posts

 

The only advice I would offer is that when I fit bessa boxes, outside, I always drilled a hole, in the bottom of them, to allow any ingress to escape. 

A draining point like this perhaps…………

 

Sparkingchip
4625 Posts

3. - 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. To ensure that condensed moisture does not accumulate, small drainage holes must be provided at the lowest parts of the system.

https://www.tlc-direct.co.uk/Book/4.5.1.htm

mapj1
4166 Posts

Advice that is not so useful if the lowest point is below the water table though. 

Tomgunn
230 Posts

Zoomup: 
 

 

The only advice I would offer is that when I fit bessa boxes, outside, I always drilled a hole, in the bottom of them, to allow any ingress to escape. 

A draining point like this perhaps…………

 

 

Hahaha, SPOT on!!! 

regards… 

Chris Pearson
3072 Posts

Even though we have discussed it twice recently, I am still struggling with the concept of forming a reasonably sealed system and then drilling holes in it.

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3856 Posts

Chris Pearson: 
 

Even though we have discussed it twice recently, I am still struggling with the concept of forming a reasonably sealed system and then drilling holes in it.

Like a bath tub Chris, the holes are only at the lowest point for drainage.

Z.

Sparkingchip
4625 Posts

Chris Pearson: 
 

Even though we have discussed it twice recently, I am still struggling with the concept of forming a reasonably sealed system and then drilling holes in it.

It will partly fill with water without the drainage holes as they also equalise the pressure avoiding water being sucked in.

Chris Pearson
3072 Posts

Sparkingchip: 
It will partly fill with water without the drainage holes as they also equalise the pressure avoiding water being sucked in.

I can understand an IP65 socket at one end being sealed (assuming no drain holes breaching the IP rating), but it would be an odd DB that was outdoors; so wouldn't the supply end be at atmospheric pressure?

Tomgunn
230 Posts

Chris Pearson: 
 

Even though we have discussed it twice recently, I am still struggling with the concept of forming a reasonably sealed system and then drilling holes in it.

 

It's what I, sparks, used to do… condensation etc - too much pressure has to be released BUT… as per usual, I could be wrong!

regards…

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