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10Mm Cable Near Hw Pipe


wellconnected

Question

I'm in the process of doing a bathroom update and this necessitates running new water pipes along behind a plasterboard wall in the hallway then beneath the (concrete) hallway floor. Total distance is around 8 metres with 7 behind an uninsulated plasterboard wall and 1 metre under concrete.

 

I also have two 10mm T&E cables to run to the bathroom - one feeding a new shower and a second running below the bathroom floor and out to an external junction box where it continues in 10mm SWA to a shed and by far the easiest and shortest route for these cables would be along the same track as the pipes but I'm concerned the heat from the hot pipe will overheat the cables, despite their being generously specced for the intended loads.

 

Am I being over cautious? Any suggestions for shielding/insulating the hot pipe? I had planned running the pipes and cables in separate plastic ducts set in the concrete about 2" apart and insulating the pipes thoroughly where they run in the stud wall.

 

 

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Gland plates are availible

https://www.tlc-direct.co.uk/Products/WKEC308.html?source=adwords&kw=&gclid=CLHXs53NrscCFUzHtAodwrMJQA

quote name="steptoe" post="392951" timestamp="1439754407"]You have said you have TNCS earthing,

Is it PME? 

You WILL have problems with exporting that.

Second point, how have you terminated the SWA at the Wiska box? 

I have not yet seen a good method of terminating a SWA at a Wiska box,  the gland thread doesn't usually protrude inwards enough and usually means using a galv female coupler, with a locknut and male coupler

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Gland plates are availible

https://www.tlc-direct.co.uk/Products/WKEC308.html?source=adwords&kw=&gclid=CLHXs53NrscCFUzHtAodwrMJQA

quote name="steptoe" post="392951" timestamp="1439754407"]You have said you have TNCS earthing,

Is it PME? 

You WILL have problems with exporting that.

Second point, how have you terminated the SWA at the Wiska box? 

I have not yet seen a good method of terminating a SWA at a Wiska box,  the gland thread doesn't usually protrude inwards enough and usually means using a galv female coupler, with a locknut and male coupler

Yes

I've seen them, but maybe it's the glands I use, they don't seem to enter the box enough to get those on, or a piranha nut either, maybe it depends on the cable size Vs box size,,, 

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I am sure the thread on glands is getting smaller/shorter, same with brass bushes

Don't even mention Curly Wurlies, Wagon Wheels, Bounty, Mars Bars, size of tube inside a bog roll, motorway services Bog Roll size, Espresso.....it is like a damp cup now

Somebody should start a thread bout things we do not like

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The thread is getting longer, the glands are getting shorter.

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Must admit I have not tried to get a SWA into a Wiska box

Will the Wiska "thicker" threaded brass plates not work instead of the weary bit of tin thing with the spade terminals?

Just a thought

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Just measured a SWA branded CW20S gland,

Thread length 10mm

Wall thickness of a 3" Wiska box, 7mm

Hardly much to get an earth on, barely more than a thread. 

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Just measured a SWA branded CW20S gland,

Thread length 10mm

Wall thickness of a 3" Wiska box, 7mm

Hardly much to get an earth on, barely more than a thread. 

 

It is touch and go and as I say, the Wiska box I used had a 'raised' part in the moulding that prevented the nut getting a decent start on the gland threads. I cut it off flush with the actual wall of the box with a Bosch Multi Cutter and that was enough to get the nut on securely. It did take a bit of patience mind you and I wouldn't have wanted to encroach any further into the wall of the box for fear of weakening it.

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I would insulate pipe anyway, it will save centrally heating the mice and make big difference to you bills for a few quid. Beyond that you are overworrying in my opinion. Just keep cable put of direct contact with pipes, and make sure there is some air movement around cables/ pipes

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I would insulate pipe anyway, it will save centrally heating the mice and make big difference to you bills for a few quid. Beyond that you are overworrying in my opinion. Just keep cable put of direct contact with pipes, and make sure there is some air movement around cables/ pipes

That's reassuring - thanks. I was reckoning that I'd be safe enough with 10mm over that distance and considering the short time a shower is actually in use.

 

The feed to the shed is of course hugely over-specced but I wanted to have a decent sized third conductor that would allow for bonding if we decided to add a water supply to the shed at some future point. Our earthing is TNC-S and the shed is wooden with no structural metal or services to worry about at the moment so I'm using the SWA armour + third core as earth connection. If, however, services are added I would use the armour as earth and the third core as a bonding connection. Hope that sounds reasonable.

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Sounds fine, but you're still relying on the cpc in the FTE under the floor which is what size?...

You can't separate the earthing and bonding like that anyway in the SWA, you must ensure that both are sized adequately for the job individually.

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Sounds fine, but you're still relying on the cpc in the FTE under the floor which is what size?...

You can't separate the earthing and bonding like that anyway in the SWA, you must ensure that both are sized adequately for the job individually.

i am aware the CPC in the T&E would be inadequate for bonding so if bonding became necessary later by added services the plan would be to run an additional single core 10mm CPC in the 'house section' to ensure the bonding is consistent throughout. Although the SWA armour is of lower rating as a CPC it should be adequate for the intended load (4 fluorescents and a ring for maybe a 2kw heater, computer printer, kettle perhaps  and that's about it) I suppose I could use SWA throughout  of course from the word go with the added benefit of greater heat tolerance near the pipes. Would that be preferable? There would still be the shower feed though and SWA to that would present termination problems at the bathroom end (can't run straight to shower unit, can't hide a JB under a floor etc and it would be unsightly surface mounted.

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How do you make it that the SWA is of a lower rating?

What rating, I'm confused by your post/terminology.

 

As far as a single cable right through, that would be my choice, I would never add a connection/joint unless I had to, IMHO it's bad design, why would you design in a potential failure point/reliably issue unless you HAD to?

 

Don't worry about the shower in FTE.

 

If you haven't bought the cable yet and you are buying SWA then it will be 90 deg. rated, whilst you can't use this for the current load rating, it could help you with the external influences on the circuit as the designer of the installation.

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probably easier / cheaper to TT the shed.

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How do you make it that the SWA is of a lower rating?

What rating, I'm confused by your post/terminology.

 

As far as a single cable right through, that would be my choice, I would never add a connection/joint unless I had to, IMHO it's bad design, why would you design in a potential failure point/reliably issue unless you HAD to?

 

Don't worry about the shower in FTE.

 

If you haven't bought the cable yet and you are buying SWA then it will be 90 deg. rated, whilst you can't use this for the current load rating, it could help you with the external influences on the circuit as the designer of the installation.

Sorry - I meant the steel armour of SWA is lower rated than one of the copper cores so wouldn't necessarily cope with an extreme fault current if used as a bonding CPC and less than 10mm. At this stage the SWA has been laid and terminates (with appropriate glands) at a Wiska JB on the outside wall of the property. The stage I am at now is continuing the feed back through the house to the consumer unit  in 10mm T&E. The possibility of extending the equipotential bonding is academic at the moment but the third conductor in the 10mm SWA would 'future proof' me in that respect. Obviously beefing up the bonding conductor from the MET to the Wiska box would also be needed but that would be relatively easy compared to upgrading a buried cable. Running SWA right through to the consumer unit would possibly have been more reliable but it would have proved rather unwieldy to install in this situation. Hope that makes some sense!

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Ok, the SWA is not "lower rated" it is merely a different type of conductor.

That is all.

The whole point of designing the installation correctly would be that the SWA WOULD carry the fault current.

Thus no different from the copper core.

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probably easier / cheaper to TT the shed.

Agreed - but I probably wouldn't trust it! That's just me though! 

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Why?

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Ok, the SWA is not "lower rated" it is merely a different type of conductor.

That is all.

The whole point of designing the installation correctly would be that the SWA WOULD carry the fault current.

Thus no different from the copper core.

Yes - absolutely. So I was sizing cable on the assumption that at some point in the future the armour would be the CPC and the third core MPB. At the moment the armour and third core are working in tandem as CPC (belt and braces!) Have I boobed there?

Why?

Oh just an irrational notion that ground conditions might be variable!

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If you look into BS7430 then you will begin to understand about how to ensure that earth electrodes are correctly installed and their performance verified.

TBH, I don't really see how you can design & install the means of earthing for an installation without the relevant guidance on how this should be undertaken.

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You have said you have TNCS earthing,

Is it PME? 

You WILL have problems with exporting that.

Second point, how have you terminated the SWA at the Wiska box? 

I have not yet seen a good method of terminating a SWA at a Wiska box,  the gland thread doesn't usually protrude inwards enough and usually means using a galv female coupler, with a locknut and male coupler

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If you look into BS7430 then you will begin to understand about how to ensure that earth electrodes are correctly installed and their performance verified.

TBH, I don't really see how you can design & install the means of earthing for an installation without the relevant guidance on how this should be undertaken.

No - well aware of issues with installation and verifying TT but as I say it would still leave me a bit uneasy about ongoing reliability (short of re-testing every few months!) and with there being no services or extraneous conductive parts at the moment I'm happy enough to export the earth. As I say, pretty much an irrational thing on my part!

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So why would you be so worried that you would feel it necessary to re-test your work every few months if it was designed and installed correctly?

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You have said you have TNCS earthing,

Is it PME? 

You WILL have problems with exporting that.

Second point, how have you terminated the SWA at the Wiska box? 

I have not yet seen a good method of terminating a SWA at a Wiska box,  the gland thread doesn't usually protrude inwards enough and usually means using a galv female coupler, with a locknut and male coupler

Yes PME - what might cause problems?

 

The gland at the Wiska box was indeed on the short side due to a raised moulding on the inside. I cut this out to get the thickness down to the rest of the box and used the optional Wiska plate with spade terminal and flylead. That got a good secure grip and termination.

So why would you be so worried that you would feel it necessary to re-test your work every few months if it was designed and installed correctly?

 

Possibility of changing ground conditions I suppose!

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However, if you have taken into account the requirements for the correct design of an earthing system, and correctly done your design FMEA's as required under statute law then what can go wrong, if the earthing system is installed in accordance with the design parameters & specification?

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However, if you have taken into account the requirements for the correct design of an earthing system, and correctly done your design FMEA's as required under statute law then what can go wrong, if the earthing system is installed in accordance with the design parameters & specification?

You're right of course!

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