17th Edition, RCD's and Cable routes

Hi,

I can't seem to see anywhere that is selling the new onsite guide yet - maybe it hasn't been printed yet!? (Where is the best (cheapest!) place to get a copy of the regs?)

I understand that all circuits that are not proved to be mechanically protected need 30mA RCD protection.

The house I have just bought has old breakers in a rewritable fuse box (Plug in replacements to the fuses, a bit like this

formatting link
But with two buttons on the front (trip and reset)) I plan to replace it with a 3 way unit, with two RCD's and a non protected section, so I can RCD the lights separately from the sockets, have the fridge and freezer on the non protected side, and have a feed to the garage in SWA off the unprotected side.

I assume the SWA is ok, as it is protected "out of the box" so does not need to be connected to an RCD in the house (It will go into a RCD or RCBO protected consumer unit in the garage, so the circuits there will be protected, and as the garage is very close to the house, the TN-S earth will be exported (I assume it is still OK to use the steel wire as earth, so I only need 2 core cable?))

If I were to run twin and earth from the unprotected side in the house, can this just be clipped to the sides of the joists under the floor, or will it need protecting even under there to be compliant?

If buried in a wall, I assume it needs steel capping, I assume this needs earthing too - if so, where to, am I supposed to cut into the CPC of the cable I am protecting, or do I need to run a separate earth cable back to the CU (if so, what size?)?

How about running it through a hole the wall to the back of an IP66 box (to then connect the SWA to, feeding the garage?), do I need any other protection here, like a short length of metal conduit?

Many thanks!

Toby...

Reply to
Toby
Loading thread data ...

==================================

formatting link
- listed as 'forthcoming - discounted by 11% to £17-80p. They take advance orders and will deliver when available. Very reliable bookseller.

Cic.

Reply to
Cicero

Not out yet. Soon (i.e. September) IIRC.

Yup. Mechanical, including burying deep enough.

Yup sounds ok so far.

Yup. Short distance exporting of a TN-S earth is usually fine. Using the armour of the cable is the best way to do it.

If it is out of reach of nails etc, then it is fine.

The more typical solution would be metal conduit (and you could use singles rather than T&E in it), or MICC, or there is a new type of earth shielded cable designed with this sort of application in mind - but I forget the source or its name). For that matter you could run SWA if the routing and bending is not going to be a problem.

If its out of reach on the side of a joist then that sounds ok.

Reply to
John Rumm

Should have also said you can surface run T&E and not need RCD protection since it is not concealed.

Reply to
John Rumm

What if it's under capping, or boxed in under plywood under the CU?

Reply to
<me9

Thanks John, all sounds sensible to me, the fact I can run surface, and not have to protect or RCD is good for the runs to the ovens, hob, fridge and alarm - will save hassle!

The new installation I am thinking of (just written it out tonight, so it may need tweaking), is as follows...(It's in a 3 bed semi)

Cable lengths are approximate, I haven't measured properly, they are probably over estimated if anything!

60A Cut-Out, earthing provided by suppliers cable sheath (TN-S)

Earth connected, via 16mm cable, to earthing block Gas main bonded to earthing block (10mm) Water main bonded to earthing block (10mm) Consumer Unit 1 connected to earthing block (16mm)

(Do these cable sizes sound OK, there are already 10mm runs to the gas and water)

Consumer Unit 1 - House

15 module, triple way, two RCD's and 1 main switch.

Section 1 - 80A/30mA RCD

32A - MCB - Ring - 2.5mm T&E - 30M - Downstairs Sockets 32A - MCB - Ring - 2.5mm T&E - 40M - Upstairs sockets 32A - MCB - Ring - 2.5mm T&E - 25M - Kitchen Sockets Spare (Blanked)

Section 2 - 80A/30mA RCD

06A - MCB - Radial - 1.5mm T&E - 20m - Downstairs lighting 06A - MCB - Radial - 1.5mm T&E - 25m - Upstairs lighting Spare (Blanked)

Section 3 - 100A Switch

32A - MCB - Radial - 4.0mm XPLE SWA 2core - 20m - Garage Sub main, Earth exported via steel wire. 16A - MCB - Radial - 2.5mm T&E - 10m - Built in Oven 16A - MCB - Radial - 2.5mm T&E - 10m - Built in Microwave/Oven 16A - MCB - Radial - 2.5mm T&E - 10m - Induction Hob 16A - MCB - Radial - 2.5mm T&E - 10m - Kitchen Fridge 10A - RCBO - Radial - 1.5mm T&E - 20m - Exterior Lights 06A - MCB - Radial - 1.5mm T&E - 05m - Alarm System Spare (Blanked)

-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-

Consumer Unit 2 - Garage (From 32A RCD in Consumer Unit 1)

5 way consumer unit - 1 Section with 100A switch, earth exported from house (TN-S) 16A - RCD - Radial - 2.5mm T&E Single Socket for freezer only (Positioned and marked accordingly) 06A - RCBO - Radial - 1.0mm T&E - Lights 20A - RCBO - Radial - 2.5mm T&E - Sockets 20A - RCBO - Radial - 2.5mm T&E - Outside stuff (Connected through various fused spurs) Spare (Blanked)

-----------------

The consumer units I propose to get are from the Wylex NH Range

formatting link
I am going OTT with the amount of ways I am using (the existing only has 5!) but does it matter / would it be better done differently, or while I am at it, why not!

I plan to document and photograph everything, to build a manual for the house too.

Thanks for any comments!

Reply to
Toby

I think you can put them in surface trunking as well if required, since there is little chance of drilling into that and not noticing!

Yup sounds ok. If more convenient you can do the main equipotential bond to both services with a single wire as long as it is unbroken (i.e. loop through the clamp on the first, and run on to the second). Obviously depends on layout if that is helpful or not.

You have not mentioned tails size. FOr a 60A supply, you could go as low as 16mm^2, however using 25mm^2 may be prudent to allow for an easy supply upgrade in the future.

Yup sounds ok, although beware there are a couple of schools of thought on how to split out the lighting. The way you have it there is very little chance of getting a nuisance trip of the lighting RCD, however if it does trip you lose all lights in one go. You could for example mix the upstairs ring and downstairs lighting, on one RCD and kitchen + downstairs ring and upstairs lighting on the other. More chance of getting a nuisance trip on a lighting circuit, but you only lose one at a time.

The posh solution would be lighting on individual RCBOs on the non RCD section. (lower trip current RCBOs (i.e. 6A) now seem to be getting more common as well)

Personally I would add an emergency light in the proximity of the CU anyway.

Yup, sounds good. Also keeps the outside stuff (higher risk of nuisance trips) on its own RCD(s).

Indeed the time and effort is much the same regardless, and a nicely segmented system is easier to maintain and test anyway.

More than you will usually get from a pro sparks! ;-)

Reply to
John Rumm

Would you ot be better splitting the lighting/power between the boards:

section 1

Downstairs Sockets Upstairs lighting Kitchen Sockets

Section 2 Upstairs sockets Downstairs lighting

So that some lighting is available if an RCD trips.

Reply to
<me9

Exclent, makes sense!

These are already installed, singally, so I don't need to bother (other than th check them, obviously!)

If it was being one in one run, if the cable was cut, can it be soldered/crimped, and still be OK?

Iam not sure acutally, I think they are 16mm, but will check, do you know the normal external diameter of 16mm cables?

Sounds very sensible, then I can just have a 2 way split board too, gaining another 2 modules (where the seconds RCD was) - not that I really need any more ways!)

I was thinking of putting one of these in the celing, over the front door, and at the top of the stairs (the front door is very near the bottom of the stairs)

formatting link
consumer unit will be in a cupboard next to the front door. (This is where the cut-out is)

I also plan to put the boiler above this, is that OK? I assume I will need to put a shelf between the boiler and the electrics, to minimise the risk of a leaking boiler dripping onto the consumer unit and cut-out?

I gess sloping the shelf slightly forward, will mean any water will run away, towards the front of the cuupboard too.

While I am doing it, it seems silly not to spend an extra few minutes taking photos, then writing it up later!

As for Part P....I assume I really do need to do this properly, as it will be a complete rewire - what is the procedure here, will it cost me loads to jump through their hoops?!

Toby...

Reply to
Toby

Trouble is with that a "fault" on the downstairs ring will turn of the lights upstairs. Plungeing anyone up there into sudden and unexpected darkness...

Personally I'd rather the lighting was not on an RCD but it appears that

17th Ed won't allow that.

Having three rings on a single 30mA trip might start to push things these days with so many devices having SMPUs and "leaky" supression components across the mains. IIRC the recomendation is for no more that 10 such devices per 30mA trip...

Reply to
Dave Liquorice

Yes, sounds like a better idea, but as John said, I can just get a two way board, and put them on RCBO's - that's even better :-)

Thanks for the reply though!

Toby...

Reply to
Toby

Okay, so I started with a three way CU, then decided 2 way, now I think I should have a single way, with a 100A switch, and use more RCBO's!

Here is the revised plan for the house CU

Consumer Unit 1 - House

14 module, 100A switch

32A - RCBO - Ring - 2.5mm T&E - 30M - Downstairs Sockets

32A - RCBO - Ring - 2.5mm T&E - 40M - Upstairs sockets 32A - RCBO - Ring - 2.5mm T&E - 25M - Kitchen Sockets 32A - MCB - Radial - 4.0mm XPLE SWA 2core - 15m - Garage Sub main, Earth exported via steel wire. 16A - MCB - Radial - 2.5mm T&E - 10m - Built in Oven 16A - MCB - Radial - 2.5mm T&E - 10m - Built in Microwave/Oven 16A - MCB - Radial - 2.5mm T&E - 10m - Induction Hob 16A - MCB - Radial - 2.5mm T&E - 10m - Kitchen Fridge 10A - RCBO - Radial - 1.5mm T&E - 20m - Exterior Lights 06A - RCBO - Radial - 1.5mm T&E - 20m - Downstairs lighting 06A - RCBO - Radial - 1.5mm T&E - 25m - Upstairs lighting 06A - MCB - Radial - 1.5mm T&E - 05m - Alarm System Spare (Blanked) Spare (Blanked)
Reply to
Toby

IIRC the regs make reference to "unbroken" connections - so this may be a case where a join is not acceptable.

about 9.1mm IIRC. (11mm for 25mm^2)

saving. Ones showing the exit routes however can certainly be in the latter category. (again depends a bit on the location and the amount of ambient light about)

Depends on your local authority and how they want to play it. In theory, you submit a building notice (

Reply to
John Rumm

The style of the printed lable has that 20's/30's look about it as well. When was this house built?

I'm not overly convinced about the braided conductor between the earth block and the incoming cable either.

Reply to
Dave Liquorice

late 30's!

Me neither!

However, I don't really want to risk disturbing it!

I will call the DNO on Monday, to ask for an isolator to be fitted, with a bit of luck, they will see how old the cut out is, and change it!

Toby...

Reply to
Toby

There we go then, orginal equipment.

They might, it maybe old but still looks pretty servicable, now if the cover was cracked, or the hinge broken. Bear in mind that changing it will almost certainly involve live working for who ever does it and the incomer is no doubt 80 years old as well and might not take kindly to being messed about with...

Reply to
Dave Liquorice

The other clue is on the patent applied for dates in the small print of the label - 1921 and 1923!

Reply to
John Rumm

These are all run with some form of protection or are >50mm from any surface?

AIUI 17th Ed says *all* circuits must be RCD protected unless physically protected or >50mm from a surface.

Reply to
Dave Liquorice

Yes, I think I can achieve this!

Reply to
Toby

What if they are clipped to the surface, and thus visible?

Reply to
<me9

HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.