help me sort out some VERY DANGEROUS electrics!

[Stephen H]

firstly the background stuff.

I've bought a house last December that has two single garages attached to the left hand side of the house. and the bedroom us on top of the twin garages.

the house was built in 1985.

One of the previous owners has seen fit to convert the garage nearest the house into a habitable room and knock through a new opening for a door from the hall. They also removed the garage door and put in a dwarf height brick wall and a new DG UPVC window.

In the mean time, the previous owner had free cavity insulation installed 2 year ago.

So far so good.

Now there is a consumer unit in this now converted garage.

as part of my efforts to update the house, i decided to update the CU unit and also move itto the hall.

This is because we want to make this room "flexible" accommodation. This may well include setting up a bedroom from time to time for putting up ill/dsiabled/elderly relatives. We would like to be able to reset any tripped RCD/MCB without disturbing the room occupants.

There was no switch isolator in the meter cupboard so I made the necessary contact with the local electricity board and they've called round and done the necessary works in order to make it safe for me to change the CU.

They have put in new 25mm tails from the cutout to the meter and also from the meter to the new 100A rated switch switch. (the old ones were 16mm)

As the old tails between the switch isolator and the old CU is 16mm, they have down-rated the original 80A cut out fuse down to 60A and put brown insulation tape on the cut out to mark this. Clearly the tails between the switch isolator and the old CU is my responsibility and I am upgrading this to 25mm and getting the board to come back and put in a

80A or even a 100A fuse.

See the link:

I have since discovered that the plaster has blown everywhere in the converted garage. The original "plasterer" has used render and then a plaster skim.

I started removing the old plaster so that I can get the room replastered. In doing so, I discovered that the meter tails had been brought through from the meter cupboard right into the room and surface mounted on the internal wall. Plastic trunking fitted and then skimmed over.....

I have also since discovered that the old metal CU is screwed directly to the breeze block wall and was just plastered around it.

The alarm panel that you see was installed only 5 years ago, which is below the current CU. The alarm installer was lucky he did not drill through the meter tails and electrocute himself when fitting the fused connection unit for the alarm panel, as there is no RCD or earth protection on these meter tails!

The link is:

some previous house owner had decided to hammer a picture nail into the wall.... *shudder*

Clearly I am going to rectify this horror.

Now having thought about this, I have three choices regarding the new meter tails.

1. Chase a channel into the breeze block walls, and then fit a length of

3mm thick 50mm wide steel plate to provide protection

1. use a steel round conduit to place meter tails through and countersink this into the wall.

2. somehow thread up via the cavity the new meter & earth tails to where the new CU will be. This is the most difficult option as I'd like to place the new CU in the hallway. There is also the issue of teh cavity insulation.

Are options 1 and two acceptable from 17th Ed wiring regs?

Surface mounting the new tails on top of the new plastering in the converted garage is *NOT* an option due to SWMBO.

Now, I know I need to fit a switch fuse within 3m of the cut out to protect the meter tails as the new CU would be in the hall, which is more than 3m away.

I prefer to not have this switch fuse present in the room. the nearest non-visible location would be next to where the CU is moving to, but that means the switch fuse is too far away from the cutout.

Now my next question is: Can I put the switch fuse in the meter cupboard or has it definitely got to be outside the meter cupboard? can the board disconnect me if they discover this or do they turn a blind eye? the network in question is Central Networks.

the least attractive alternative would be to put the switchfuse where the old CU unit is, and then I can run from there to where the new CU is going. at least the new switch fuse will be much smaller than the old CU.

The alarm panel is being relocated to the loft.

Fortunately for me, all the current T&E from the old CU location goes past the new proposed CU location so it will be a simple matter to shortening the cables and so no junction boxes will be needed for extending cables.

I am aware of my obligations under part p and will get my work inspected and tested.

All feedback welcome.

Regards,

Stephen

[jrwalliker]

How about using properly earthed SWA cable? That would be adequately protected, but it would be quite stiff. You would need a small metal box at each end to mount the termination glands.

Why would anyone object to this? It seems the ideal location.

John

[Tim Watts]

For 25mm2 SWA, "stiff" is an understatement.

OP: can you not run the tails in surface trunking?

Don't stuff them up the cavity - this is now frowned upon for more than one reason.

[Owain]

Well, yes, but it is right below a visible accessory!

Would SWMBO accept some nice chamfered dado trunking if painted to match the decor? Or even a shallow full height cupboard to enclose the CU and cables etc?

Owain

[Stephen H]

how bing are these boxes and are they direct burial type?

that will be a thick cable to chase a channel in the thermalite blockwork.

I don't want to stuff them up the cavity either for several reasons

a) thermal cavity insulation and thermal de-rating of the cable b) there will be wall ties obstructing a straight route c) the new tails would need to go up to the cieling - floor void to go across to the hall. d) the plastic cabling could act as a condensation/moisture route between inner and outer leafs e) the rough ceramic brick/block surfaces could tear the tails insulation f) with all that cavity wall insulation in the way for pushing three tails through......

It appears to be the local electricity grid that makes a song and dance about this. apparently if they find stuff that shoudl not be in a meter cupboard, then can disconnect you from their network.

incidentally i have one of the those energy monitor clamps and transmitter around the live meter tail.... they don't object to that being in the meter cupboard....

[Stephen H]

thanks for the suggestion of surface mount trunking.

Considering its normal practice to bury T&E cables for either lighting, sockets or cookers or showers or immersions in plastic with RCD protection or in galvanised metal trunking in plaster, this begs the question of why we can't do the same for meter tails and earth tail provided either suitable mechanical protection such as 3mm sheet steel to cover said tails or electrical protection such as 100mA RCDs* is employed

*Assuming CU unit has 30mA RCDs and discrimination is required between circuits.

[Stephen H]

after some more searching,

I came across this:

lays down the requirements for burying cable in plaster.

It makes no reference to the type of cable used, i.e. meter tails or T&E.

There is also no mention of using SWA.

So it appears that if I use one of the following (for a ordinary person, not a trained or an instructed person environment):

earthed metal cover earthed metal conduit earthed trunking/ducting mechanical protection bury in the safe zones & use S type 30mA RCD (not to be used as personal protection which is OK as the new CU will use nothing but RCBO's for max discrimination. (this RCD is for where

so an earthed 3mm steel plate would appear to satisfy two of the above to more than satisfy the regs.

I quite like the idea of using an S type 30mA 100A RCBO in place of a switch fuse but probably too big for meter cupboard or hard to buy.

comment welcome.

Stephen.

[dom]

I'm wondering how your meter tails ended up in the state they are in.

I could believe a gormless plasterer might just skim over exposed wires. But the tails should never have been surface mounted and unprotected in the first place.

Clearly fixing this is your most urgent issue.

Regarding moving the consumer unit though, is it really worth it? How often do you realistically have to access the consumer unit to reset a tripped circuit?

[Tim Watts]

The 100mA RCDs you speak of are usually Type S time delayed - which makes them unsuitable for the protection of buried cables (by the book).

If you used a 40mS 100mA RCD, it would almost certainly trip when any 30mA

40mS RCD downstream did. Therein lies the problem.

However, mechanical protection does solve the problem - the only issue with DIY bits of iron is getting into a debate with the DNO or an installation tester about whether a particular method meets the regs.

Heavy wall (ie any modern) steel conduit does - but bending it will not be fun and neither will jointing it.

I am not sure if metal trunking, buried, meets the regs. I think it probably does, but wait for Adam or someone to comment. The advantage would be - easier to joint (hacksaw and corner pieces); could be skimmed over; easier to lay the tails in, then fit the lid.

I would earth both of the above. Tail are double insulated - but if an SDS drill dies puncture either, it will blow the cutout fuse when it hits live.

[Andy Burns]

When it was a garage, I suppose they were just surface mounted and nobody cared, they seem to be covered by plastic capping which might have been there all along, or added before plastering when it was made into a habitable room

That's allowable isn't it? Plenty of tails run exposed and self-supported rather than fixed in any way.

[Andy Burns]

Better state than these ...

[ARW]

Split concentric cable (BS7870) may be a better option.

[ARW]

Hi Stephen

I'll try and clear a few things up for you.

Look again at your link.

522.6.6 i) Please note that this lists "the types of cable with earthed metallic sheathing" suitable for burying in plaster at less than 50mm depth. This is NOT the same thing as an earth metal cover shoved over a PVC cable. It only applies to the BS cables listed in that part of the regs. The BS 5467 cable is SWA cable. So just to be sure - the earthed matallic covering ONLY applies to the BS cables listed in that reg - it's the cables earthed metallic covering that provides the protection and NOTHING else.

parts ii) and iii) cover the way to used earthed coverings that are not a part of the cable as in part i). I would suggest that you forget parts ii) and iii).

Now part iv) This is where 3mm steel may be of use to you. 3mm steel (and there is no requirement to earth it) is often deemed to be sufficient protection against mechanical damage. You could cover 25mm tails with 3mm steel and have the tails less than 50mm below the surface.

Now you need to read 522.6.7 in the link for the full picture.

Post back if you are not sure.

And I would forget about installing a RCD at the head end of your supply.

Cheers