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Topic Title: Is electric cable on block and beam floor OK?
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Created On: 20 August 2013 12:55 PM
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 20 August 2013 12:55 PM
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jonbey

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Joined: 20 August 2013

A builder has installed cable to a suspended block and beam floor, which is then covered with a waterproof membrane, then with celotex insulation, and screed will go on top.

Somebody on another forum said that this was not good. However, I am trying to find out if it is just not good, or terrible.

If I can post a photo I will





I understand it may not be perfect, but need to know if I am going to have to request that it is all changed, with conduit etc.

many thanks
 20 August 2013 01:13 PM
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OMS

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Well, it's as rough as a badgers to be honest - it's up to you to determine if the cable type and installation method are suitable that during installation and in operation the cable doesn't suffer damage.

Given every ***** in creation is walking on that cable and will soon be barrowing screed in there, over the cable, and said screed may also be caustic, then I suggest a bit of protection wouldn't go amiss. Personally speaking, conduit is the only realistic way - your choice if it's steel or PVC


Take a look at regulations

522.5.1

522.6.1

522.8.1

Regards

OMS

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Failure is always an option
 20 August 2013 01:19 PM
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AJJewsbury

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I'm not worried about the beam & block - but burying T&E cable in concrete screed I'm pretty sure is a no-no. It's OK in plaster but concrete is different (at least so says the On Site Guide). I'm presuming it's a conventional concrete screed, rather than a gypsum one.

Also any plans for underfloor heating?
 20 August 2013 01:21 PM
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Parsley

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522.8.7 A wiring system buried in a floor shall be sufficiently protected to prevent damage caused by the intended use of the floor.

Regards
 20 August 2013 01:23 PM
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normcall

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I suppose if the builder has designed and installed the installation exactly what is your role in the saga?

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Norman
 20 August 2013 01:27 PM
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AJJewsbury

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I can't help thinking it would be easier to go horizontally between the sockets (and then up & over the door at ceiling level).
- Andy.
 20 August 2013 01:50 PM
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jonbey

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Hi, my role is home owner - I am here for advice not as an electrician (hope that is allowed, your advice so far has greatly reduced my stress levels).

Above the block and beam is a water tight sheet and Celotex insulation, so screed will not be in direct contact with the cables.

Photo of floor at the moment:



I did not get a photo of the sheet, but it reminded me of pond liner - thick black waterproof membrane.

Edited: 20 August 2013 at 02:23 PM by jonbey
 20 August 2013 03:05 PM
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OMS

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So now the cables are covered on at least one side by thermal insulation and now exist right outside the "dry envelope" of the building - and actually penetrate the DPC

It's a rough as can be, to be honest, if they must be in the floor then they should, by any metric be in conduit, and above the DPC . Ideally they shouldn't be down there at all - what's above that precludes them going that way ?

Regards

OMS

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Failure is always an option
 20 August 2013 03:11 PM
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jonbey

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I do not know why the builder chose to do it the way he did. Above is a vaulted ceiling, no reason why they could not go up and over IMO, I guess it is just the way the builder does it.

I have contacted a local electrician who will look tonight after they leave. It's going to cost £70-£140 (depending on if they can inspect and advice in under and hour or under 2 hours) but I guess it needs to be done.

The builder will be getting a "Part P" he knows to sign it off. So I think I need somebody independent (and hopefully honest) to advise.

Should have been properly looked at before the walls were plastered really, but I am learning this as we go along - I was only alerted to a possible problem when I proudly posted a photo of the work done the internet!
 20 August 2013 03:21 PM
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AJJewsbury

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OK the celotex (presuming it's going to be properly sealed at the perimeter) should mitigate both the chemical action and mechanical damage during the screed lay. Thermally it's not ideal, but the cables should be able to loose heat into the beam/block so it's probably OK on that score too. Presuming they've not gone to the trouble of chasing out a groove on the underside of the Celotex for the cable, then the cable with be under a bit of compression from the weight of the floor - that I'd be a bit concerned about - both in terms of bits of debris (e.g. bit of grit from the blocks or edges of the beams) being pushed into the cable, so piercing the sheath and possibly insulation; also when the insulation/sheath softens when the cable is subject to fault currents, the weight distorting the overall cable cross section.

In terms of having evidence to wave about under people's noses - it's tricky as it's not a recognised 'normal' installation method. How about asking the cable manufacturer if they'd recommend their cable for such a use? I suspect they'd say they wouldn't.

- Andy.
 20 August 2013 03:35 PM
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jonbey

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I think there is some cable in the garage still, I will see if I can get the details.
 20 August 2013 03:39 PM
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perspicacious

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"The builder will be getting a "Part P" he knows to sign it off."

Welcome jonbey

Is:
1) the builder doing the electrical work and he is a "member" of one of the schemes
2) the builder doing the work and getting a "mate" who is a scheme member to sign it off for him
3) the builder is subcontracting the electrical work to a scheme member or
4) the builder is getting a non scheme member to do the work and getting a mate who is a scheme member to sign it off?

There may be more combinations but you get the idea

I'd find out which scheme will be on the "certificate" and forward your photos to that scheme and ask them to pass comment on one of their member's work.......

Regards

BOD
 20 August 2013 03:50 PM
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jonbey

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No. 2.

The builder has been doing extensions for about 20 years and always does the electrics. He actually said that he chose not to do the course to get properly qualified due to the time and cost - he prefers to pay somebody else to test and sign it off.

However, the building inspector did say (on the phone) that she would have expected an inspection to take place before the insulation was placed down. The inspector will now only be able to check that the cables are operating properly, but not inspect how they are laid (which seems important to me!).

Once I have the certificate I will do what you say - who are the bodies are there in the UK which provides these Part Ps? I will get all their details together in preparation to contacting one of them.
 20 August 2013 04:09 PM
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perspicacious

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I'd find out which scheme will be on the "certificate"

"he prefers to pay somebody else to test and sign it off."

"Once I have the certificate I will do what you say "

Too late, that's why I posted will be ie in the future not after the work "can't" be corrected without major upheaval........

I've got to go out now but a quick "google" will list the schemes and I recall only one of the schemes condones its member's signing off work that isn't their's on the proviso that the member is activily involved at all stages of the work.

Bare wires can pass all intrument tests and one forum contributer who I dare say will be posting on this topic this evening, uses the expression "Mk 1 eyeball" as the first "test"....

Regards

BOD
 20 August 2013 04:15 PM
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rocknroll

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Brushing aside all the techno bull that is starting to appear the simple answer is the cables will probably be ok installed this way for donkeys years to come, but it is not 'good practice' to install cables in the floor which is likely to be covered in concrete etc without some form of covering like plastic conduit etc;

regards

-------------------------
"Take nothing but a picture,
leave nothing but footprints!"
-------------------------
"Oh! The drama of it all."
-------------------------
"You can throw all the philosophy you like at the problem, but at the end of the day it's just basic electrical theory!"
-------------------------
 20 August 2013 04:18 PM
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AJJewsbury

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Would you really want U shaped conduit passing through the thermal envelope? Sounds to me like an ideal place to accumulate condensation - and PVC cables don't like being immersed in water long term.

- Andy.
 20 August 2013 04:33 PM
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OMS

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Originally posted by: rocknroll

Brushing aside all the techno bull that is starting to appear the simple answer is the cables will probably be ok installed this way for donkeys years to come, but it is not 'good practice' to install cables in the floor which is likely to be covered in concrete etc without some form of covering like plastic conduit etc;

regards


Come on, Rock - you know, and I know you know, that what you've just looked at in those photo's is about as rough as it gets - you wouldn't put it in that way and I'd be pretty certain you wouldn't have put up with that in your recent new build.

Regards

OMS

-------------------------
Failure is always an option
 20 August 2013 04:58 PM
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rocknroll

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I am not disagreeing that it is rough just making a point that cables in far worse conditions than that still give years of service, true a few years ago if I was looking at that I would want the cables protected or re-routed above.

We dont know what is the stage of the build these may be early pictures and the floor is down.

regards

-------------------------
"Take nothing but a picture,
leave nothing but footprints!"
-------------------------
"Oh! The drama of it all."
-------------------------
"You can throw all the philosophy you like at the problem, but at the end of the day it's just basic electrical theory!"
-------------------------
 20 August 2013 05:35 PM
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peteTLM

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Its rough as hell, and 'his mate' who will be signing off should have his head tested and his eyesight, and he knows bloody well he shouldnt be signing off someone elses work.

Conduit would be the way to go.

Ive had to replace a few cables installed like this over the years done by others. 20 years is usually enough time for the concrete to get through the cable.

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Lack of planning on your part doesn't make it an emergency on mine....

Every man has to know his limitations- Dirty Harry
 20 August 2013 07:06 PM
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jonbey

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OK, I had some electricians come and check the work. They're opinion was that the work was acceptable, but recommended that I get soem 25mm capping and put that over the cable that is under the insulation / screed so that any pressure over time is reduced. They said that once screeded the will be no movement, the only real concern is the weight of the screed floor on the cables.

So I am off to find some myself and put it under the insulation on top of the cables.
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