Domestic Departure from BS7671 - Advice

[SparkyChick]

Hi all,

As the title suggests, I'm looking for a little bit of guidance.

Long story short... kitchen remodel, was asked to install a heavy duty supply for an induction hob on short timescales as ceiling was going to be closed.

Only sizeable cable I had to hand was 10mm.

Now, in a happy turn of events, it turns out that the induction hob isn't that hungry and only needs to plug in, but the oven and microwave also require supplies. None of them are over 16A.

So my original plan was to install a BG shower CU, switch out the breakers for 16A (one for each appliance) and supply this using the 10mm on a 50A breaker from the main DB. The new CU was to be mounted on the wall, making an obvious accessory safety zone.

However, due to the construction of the kitchen units, I felt it better to have the CU inside a cupboard rather than cut a portion of the backboard away.

Where I'm seeking guidance is that this now means the 10mm is concealed in the wall, from ceiling to just below the top of the cupboard. Along the rest of it's run, it is installed in a manner (i.e. it's not at risk of damage and it's not concealed in a wall) that means it's fine to be connected to the non-RCD side of the board (the new CU has RCD protection in it).

So I have a length of cable about 10-12" buried in the wall. Due to it's location I don't believe it is at risk of being damaged by screws as it is unlikely anyone will want to hang anything there because it's effectively behind the cupboard.

I have placed a warning sticker on the top of the cupboard (Danger Concealed Cable - This includes an arrow aligned with the vertical drop of the cable). I'm going to record full details on the certificate of the location of the cable and my reasoning as to why this is acceptable.

Acceptable or not? Is this kind of departure allowed in domestic and if so is it sufficient to include your reasoning in the certificate or is there a template risk assessment I would need to use?

Your comments and thoughts are most welcome

 

[SparkyChick]

I'd look at more substantial methods of protection to satisfy the requirements of the regs.

Any suggestions? Short of hacksawing some 25mm conduit in half lengthwise, I'm a little short of ideas. I have out of interest learnt how easy it is to drill through the capping without really trying, so yes, I know where you're coming from.

 

[SparkyChick]

what about putting a big f**k off big arrow on the wall for that then ,unless to have a head like a giraffe.

The cable runs about 10-12" in the wall... from the ceiling to just under the top of the cupboard... if you're up there to drill a hole, I think a yellow warning sticker will stand out (at least until it's covered with 10+ years a grime).

 

[Andy78]

Any suggestions? Short of hacksawing some 25mm conduit in half lengthwise, I'm a little short of ideas. I have out of interest learnt how easy it is to drill through the capping without really trying, so yes, I know where you're coming from.

Either fully enclosed in earthed conduit or I know there are companies that sell substantial
shields/capping for buried cable, mostly employed for buried tails where RCD protection is not desirable.

 

[Strima]

To answer your specific question Strima... no it cannot be exposed. Client's wife is a bit OCD about cables and holes in walls.

Part of the reason the unit was moved into the cupboard was because it was there with three lengths of T+E hanging out of it ready for the terminations and it freaked her out a little, so all the cabling has to be hidden once the kitchen is finished.

Lovely couple, just a little crazy

What about some anti-vandal guard, you'd have trouble sticking a nail through that...

RONBAR FACTORS LTD UK Manufacturing supply for electrical wholesalers - Anti Vandal Guard - http://s413652122.initial-website.co.uk/products-1/anti-vandal-guard/

 

[buzzlightyear]

The cable runs about 10-12" in the wall... from the ceiling to just under the top of the cupboard... if you're up there to drill a hole, I think a yellow warning sticker will stand out (at least until it's covered with 10+ years a

so that will be a rcd then !

 

[buzzlightyear]

What about some anti-vandal guard, you'd have trouble sticking a nail through that...

and anti climb paint ,well she many has well go the full hog then .

 

[Richard Burns]

A short section of 3mm thick steel C section over the cable and plastered over would obviate the need for an RCD, since it is a variation you can clearly charge the extra for this protection.
It would however be up to the installer to assess the level of safety as meeting the requirements for a departure if you were not to do this.

 

[PEG]

It's either metal-detection gear,at each door to the kitchen,to prevent drilling equipment being brought in...

...or upstream protection. If you are concerned about this situation,i would aim for the latter

 

[SparkyChick]

I think I'm going to cut a length of 25mm conduit and slice it open with my grinder, cutting a slot big enough to slip over the cable. Drill a small hole and earth it with a crimp and self tapper to some 2.5mm earthing cable. Being sure to file off the end of the screw.

Thanks for the advice guys, much appreciated.

 

[SparkyChick]

Either fully enclosed in earthed conduit or I know there are companies that sell substantial
shields/capping for buried cable, mostly employed for buried tails where RCD protection is not desirable.

Is this the sort of thing you were thinking of Andy?

16mm Galvanised Cable Protectors Sheathing - http://www.directchannel.uk.com/gs9-tail-cable-protectors/16mm-cable-protectors-Sheathing

 

[Andy78]

Is this the sort of thing you were thinking of Andy?

16mm Galvanised Cable Protectors Sheathing - http://www.directchannel.uk.com/gs9-tail-cable-protectors/16mm-cable-protectors-Sheathing

Not personally used any but that's the sort of thing. Others might know better as to specific products. I do notice that one is 1.5mm thick where the regs use 3mm steel as an example of suitable penetration protection.

 

[Richard Burns]

I think I'm going to cut a length of 25mm conduit and slice it open with my grinder, cutting a slot big enough to slip over the cable. Drill a small hole and earth it with a crimp and self tapper to some 2.5mm earthing cable. Being sure to file off the end of the screw.

Thanks for the advice guys, much appreciated.

Remember a 2.5mm² protective conductor not part of a cable would need to be protected against mechanical damage, 4mm² otherwise.

 

[SparkyChick]

Remember a 2.5mm² protective conductor not part of a cable would need to be protected against mechanical damage, 4mm² otherwise.

Good point... I have a reel of 4mm for just such occasions

 

[Gavin John Hyde]

A bit out there and not considered in the regs!! but have you considered kevlar or composite sheets? they come in thicknesses of a couple mm, you can take back the top layer of plaster around the cable then apply the small sheet over the chase... using expoxy resin/adhesive affix to wall over cable and either side. a bit of epoxy over top its like steel and bullet proof! a drill wont go through that easily... then apply pva to the top, its then good for a skim of plaster to bring flush with rest of wall, Its what is used in forces to repair holes from things that go bang! so clearly strong enough, the sheets are a bit of a bugger to cut to size though but a small one is about a tenner online and epoxy is everywhere in shops.
I used it once upon a time to protect a wiring loom on some equipment, wrapped it up in the kevlar sheet, applied the 2 part epoxy and was good for use. idea being to protect it from potential damage in event of a explosion or blast damage.

 

[Leesparkykent]

PRODUCTS | TridentSections - http://www.tridentsections.co.uk/press/products/

My local electric centre/eddies orders it in for me. There is a video off the stuff on the link below.

Meter tails & Protection - https://www.electriciansforums.co.uk/threads/meter-tails-protection.124385/page-2