Domestic remodel - Sanity check on a couple of things

[SparkyChick]

Hi all,

Currently quoting for a fairly extensive remodel of a kitchen diner, and I have a couple of things I'd appreciate a sanity check on.

1. Structural steel bonding - My brain is telling me based on what I've read and understood that I don't need to bond the new structural steels. They aren't in contact with the ground, but my heart is telling me that just seems wrong somehow. One of the beams is going to have it's cavity acting as trunking effectively since it's the path of least resistance from one side of the room to the other and so my thinking is, I should bond it to ensure a good earth path in fault conditions.

2. Sanity check on a cable size - New oven, 22.2A (max, no diversity factored in at all). 6mm can handle it, but obviously running a 20A breaker at that is not great long term, so 32A breaker required. Since 6mm can only handle 27A when in a ceiling with insulation (ref method I'm going to be encountering), my only choice is 10mm. Voltage drop is fine either way, it's just the potential overload situation. So 10mm is the correct choice as far as I'm concerned.

3. There is going to be some under cabinet lighting. To future proof, I am going to suggest that the supply for this (coming from a 6A lighting circuit) is exposed in the cupboards as 13A unswitched outlets since then the customer can change the lighting to their hearts content. My concern though is if they stick something other than lighting on it. 1.5mm is fine generally, and can handle 13A in the ceiling with insulation. So my brain is saying this is fine, but for some reason it just feels wrong. For that reason I was considering providing the supply by 5A round pin outlets, but that raises the issue of the 6A breaker. I have very limited experience of round pin outlets. 5A is obviously the continuous rating, try as I might, I can't find any information about overload characteristics, so I'm wondering what you guys think?

Whilst it's a fairly big job (by my standards so far), the rest of it is straight forward, it's just these three niggles I could do with a bit of feedback on.

Comments and thoughts welcome

 

[LankyWill]

1. i wouldn't bother bonding the steel
2. 20A should be fine with diversity but remember hager do a 25A breaker
3. Terminate on top of the cupboards into a j501- kitchen cupboards have a slight cavity down the back anyway.

 

[Deleted member 72666]

I wouldn't bond the steel work if it's not extraneous but I would earth the one that would be acting as a trunking by carrying cables.

 

[Midwest]

Terminations for under cupboard lighting on top of wall units, keeps all the old lengths of manufacturers leads, drivers/transformers out of the way of prying hands. They look a right mess, underneath wall units, generally visible to someone sat down at the table in a kitchen diner.

PS Wall units do have a small service void behind them, but you'll have to get the kitchen fitter to cut a small notch at the top of the unit, and the bottom brace to allow for the lead/supply cable through. PPS supply the leads to the kitchen fitter, to install them when the wall unit is put up, securing top an bottom temporarily with duct tape.

I use Click Flow CT102c, if supplying drivers/transformers.

Re the cooker supply, from Table 4D5, reference method 100 gives 6mm ccc of 34a, and 101 of 27amps (Table 4A2 flat cable installation methods). I've read before, that a ceiling void without any insulation, should be treated as rm A, because of the lack air circulation and heating pipes etc. Which gives 6mm ccc of 32amps. What sort of property is it?

 

[Wilko]

Agree 6mm and 32A OCPD seem appropriate. Where insulation has been a worry I deploy a batten and get it away

 

[David M]

I wouldn't bond the steel unless it tests out to be extraneous.

In my opinion 10mm2 for the cooker is overkill in this situation.
Though this said, its your design and you should go with what you feel is right. So long as the installation complies with the current regs, there is nothing stopping you doing the cooker circuit and the lighting circuit your own way.

 

[Selfmade]

Why all the talk of diversity? This is a single load so diversity is not applicable - not like a cooker with 4 hobs, oven and grill, which will never all be on at the same time. If this is on, it's on, and drawing 22A. As others have said, overload is not an issue so I'd go with 6.0mm2 and 32A breaker.

You can get 13A non-standard sockets (with a different shaped earth pin). Scolmore make them and I believe MK do as well. Maybe a bit pricer than 5A though.

 

[SparkyChick]

The job is nearly completed, just some switches on the first floor and a socket to move and I'm done... apart from second fix once the kitchen is installed.

I actually went with 10mm for both oven and hob in the end. The hob needs it, the oven to give some headroom for the future (based on how much a of a pain in the a$$ it is with the cable runs around steels etc.) and because of insulation present in the voids.

Been a nightmare job, longer than I expected due largely to finding cable runs that fit safety zones etc., and the need to extract some cables from the dot'n'dab gunge so they were long enough for junction boxes/re-termination. Thankfully, didn't have to run an entirely new ring because the existing downstairs ring just served the ground floor (and yes, ordinarily you'd expect that, but it's a three storey house so downstairs is a little ambiguous).

Thanks for all your insight chaps, much appreciated.

 

[Midwest]

Why all the talk of diversity? This is a single load so diversity is not applicable - not like a cooker with 4 hobs, oven and grill, which will never all be on at the same time. .

Disagree, most electric ovens and hobs can have diversity applied.

 

[Midwest]

The job is nearly completed, just some switches on the first floor and a socket to move and I'm done... apart from second fix once the kitchen is installed.

I actually went with 10mm for both oven and hob in the end. The hob needs it, the oven to give some headroom for the future (based on how much a of a pain in the a$$ it is with the cable runs around steels etc.) and because of insulation present in the voids.

Been a nightmare job, longer than I expected due largely to finding cable runs that fit safety zones etc., and the need to extract some cables from the dot'n'dab gunge so they were long enough for junction boxes/re-termination. Thankfully, didn't have to run an entirely new ring because the existing downstairs ring just served the ground floor (and yes, ordinarily you'd expect that, but it's a three storey house so downstairs is a little ambiguous).

Thanks for all your insight chaps, much appreciated.

Yep kitchen refurbs aren't so easy, but done properly are not problematically, at least not for the next electrician who comes along in ten years time. Unless your are a kitchen fitter/bodger, who doesn't care less

 

[SparkyChick]

Well, I hope I've done alright. Much of it is labelled, the ring runs logically around the room, shame the cables can't. The only thing that does ruffle some feathers I think is some cables just pass through back boxes, mainly to keep them in safety zones and to keep the ring sequence logical. There are quite a few lighting cables, but the wiring concentrates in one place (a nest of Wago boxes secured to a joist which provide the wiring centre for the lighting).

Customer is going to get some annotated plans showing junction box locations and the safety zones being utilised. There is one place I'm a bit concerned about cable location where I think a dot'n'dab blob pushes the cable slightly out of the zone created by the accessory. Been thinking about the long drop for the hob supply which runs in the zone created by the window edge... when that edge finishes, the zone ends, so am going to pop a single gang back box and cable outlet face plate on to create a zone.

Unfortunately, couldn't get enough length on the existing ring connections in and out of the kitchen, so have had to use Wagos, lever not push, to connect the ring. Would have preferred not to, but just couldn't recover enough cable from the clutches of the dot'n'dab.

Some pics from a couple of days ago, constructive criticism is welcomed

Since these were taken, the lighting circuit has had all accessories connected, junction boxes connected to the ends of the floating cables (awaiting instruction from the client for locations) and it's been tested. All major cable runs for the ring and cooking appliance supplies have been IR tested and confirmed good.

 

[Wilko]

Nice

 

[Specialist]

I'll second that. But Black cable ties on White trunking. I mean really what were you thinking ?

 

[David M]

Looks ok to me,

Did you intend the accessories to be so close together? I assume you set the back boxes at a distance apart that would enable the face plates to be almost touching? this is fine provided that any future face plate is of the same size. I know some decorative ones can be larger.
I do quite a lot of kitchen re-furbs and often do the whole job including - electrics, plumbing, joinery and tiling. In my experience generally its easier for the tiler or profile glass cutter, if there is a slightly larger gap between accessories. It also tends to make for a neater job of the tiling or splash back, without much, if any detriment to the electrical accessory appearance. (obviously assuming there is going to be some sort of splash back/up stand)

 

[SparkyChick]

Thanks for the advice on the spacing, personally I wouldn't want to be filling in the gaps. The central cluster next to the window is a real mess as it practically fell apart during cutting.

Personally I would have spaced them out a bit more, but it's what the client wanted. Pairs of double gang sockets, sounds like they want them to be mostly hidden behind things.

 

[Midwest]

Re spacing of back boxes, I use these Home - http://www.spacerconnect.com/index.php/en/

They come in two sizes, one for accessories to be sit nest to each other, another so there is a decorative gap between them. Tend to use two to join back boxes, so there's no likelihood of movement. I also learnt to use laser level, to ensure the boxes line up with tiles & upstands, as long as the kitchen fitter does the same with his floor units!

I did see you used some oval conduit, is that for u/c lighting?

Only real question I have, is the main switch in the new CU with RCD supplying two MCB?