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

 

[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

 

[Pete999]

yeah ,to what ?

Er a plug!!!

 

[Midwest]

You bunch of b******s, you told be my 3' foot of cooker cable had to go on an RCD

Is the old CU a Memera 2000? If the mcb's are Eaton ALB, they have a rcd field kit to fit. They are big & bloody expensive mind.

 

[SparkyChick]

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

Just watched the video you posted... that looks to be just the ticket.

Going to have a word with one of my wholesalers this morning and see if they can get it.

Thanks

 

[SparkyChick]

You bunch of b******s, you told be my 3' foot of cooker cable had to go on an RCD

Is the old CU a Memera 2000? If the mcb's are Eaton ALB, they have a rcd field kit to fit. They are big & bloody expensive mind.

Yes, it's a Memera 2000.

Just looked for that field kit... holy cow!

Think I'll source some of that capping LSK recommended

 

[Octopus]

I see this sort of issue as a failure of the regs ............. at a time it seems more and more people don't have the regs, let alone apply them we are having a debate about a short length of cable from the ceiling down about 8 inches ...................... and there is a warning label.

Madness

A bit like the 18th suggesting that all lighting circuits must be RCD protected - even if its surface mounted cabling!

 

[Octopus]

Or fit a Wylex RCBO?





Saw this just yesterday!

 

[SparkyChick]

I see this sort of issue as a failure of the regs ............. at a time it seems more and more people don't have the regs, let alone apply them we are having a debate about a short length of cable from the ceiling down about 8 inches ...................... and there is a warning label.

Madness

A bit like the 18th suggesting that all lighting circuits must be RCD protected - even if its surface mounted cabling!

I completely agree.

 

[The Ghost]

So why can't you move the 50a supply to the RCD part. Sorry if I am misunderstanding here. Anyway what about a risk assessment to be filed with the EIC?

 

[SparkyChick]

So why can't you move the 50a supply to the RCD part. Sorry if I am misunderstanding here. Anyway what about a risk assessment to be filed with the EIC?

I've not checked yet, but my gut feeling is it won't have a sufficiently high current rating. If it does, then I probably will which opens the door for discrimination issues between the RCD in the main board and the sub-board (but I can live with that given they are both access from the same room of the house).

With regards to the risk assessment... this is where I was going in my OP. It could just be my choice of 'Departure' as the description of how I would approach it sent the discussion in the wrong direction.

My thoughts are that due to the location, the fact it is highlighted with a yellow danger label, it is unlikely to present a significant risk with regards to penetration of the cable... primarily due to the fact that you're not going to hang a picture there or fix anything there because of it's inaccessibility during normal use.

 

[The Ghost]

I think in planning an installation it is wise if not even required to take into account the life of the installation. So it could be there some years. They may sell the house and someone new comes in to refurbish the kitchen. What are views in that scenario as the cupboard/label will be gone?

 

[davesparks]

What are views in that scenario as the cupboard/label will be gone?

To remove the cupboard they will have had to isolate and remove the CU which is mounted in the cupboard, therefore they will be aware of there being a cable there and have isolated it.

 

[SparkyChick]

So, an update...

The issue of capping... none of my local wholesalers had anything resembling the capping LSK has suggested and I would go so far as to say they didn't understand why standard capping wasn't good enough until I explained it was a requirement for avoiding RCD protection on cables buried less than 50mm from the surface. If I want it I'm going to have to purchase directly or find someone who can ship it.

I ran the numbers on the board and initially concluded that the main switch (100A) and the RCD (100A) (which upon closer inspection had spare ways) would be pushed over the edge, so I picked up another board, henley block, new tails etc. But I also picked up my OSG and then re-ran the numbers and my initial view was a little off.

The existing board and the RCD had sufficient headroom to allow me to utilise a spare way so the cable is protected by an RCD at the origin, so everyone's happy

I was a bit concerned about the overall load on the CU but I think on reflection I was more concerned than I should have been as what's actually happened is a 32A cooker circuit has been replaced by two cooking appliances (rated 15A and 16A), the stand alone microwave is going (one of the new appliances is a fitted microwave) so all that's been added is the hob.

And to boot, it appears based on the test in GN8, with a resistance to the MET of 52k ohm, the water doesn't need it's bonding reconnecting which begs the question... why was it bonded in the first place?

So all in all, not too bad a day despite my concerns about this.

Thanks for all your input chaps.

 

[Octopus]

What does your scheme suggest?

 

[SparkyChick]

What does your scheme suggest?

About the capping?

 

[Octopus]

About the capping?

Yes - or omission of it!

 

[Midwest]

And to boot, it appears based on the test in GN8, with a resistance to the MET of 52k ohm, the water doesn't need it's bonding reconnecting which begs the question... why was it bonded in the first place?

That's because its the way its always been done, rightly & wrongly. Not withstanding the merits & correct procedure, will continue to be the case.

 

[The Ghost]

I remember a time when you were in danger of getting the cutlery bonded if you weren't careful. A very contentious and misunderstood area for a lot of electricians. I use that word advisedly!

 

[SparkyChick]

Yes - or omission of it!

I haven't spoken to them about it.

The simplest solution was RCD protection at the origin. Which I was able to achieve despite my belief to the contrary last night.

 

[westward10]

I haven't spoken to them about it.

Wise move.

 

[SparkyChick]

Wise move.

They are my last resort... I prefer to use the collective wisdom of you chaps. Far more reliable source of honest constructive feedback (for the most part )