Re-wiring and Part P etc

[Brett Jackson]

Hi All,

I've not done any serious wiring now for a few years the last time being when I re-wired by previous house prior to all this Part P business, anyway now I've moved and I need to do it all again...

First thing to go is the fuse box. I can't seem to find any clear guidance as to how I should utilise the 2 RCD's that you get with a '17th edition' CU. There also seems to be some conflicting info (or more probably some misunderstanding on my part) on the uk.d-i-y wiki regarding what circuits should be RCD protected. It reads like 17th ed. introduces some more stringent directives as to the protection of circuits by RCD where T&E and other unprotected cables are buried in walls below a certain depth, yet there is a suggestion that lighting and some other circuits should remain unprotected. So, how would I arrange my CU wrt the 2 RCD's and un-RCD'd circuits? I'm going to do the re-wire stage by stage as I re-decorate each room, so I'll probably end up with a couple of lighting circuits and half a dozen radial circuits (one per room) for the sockets, plus a ring for the kitchen, CH, oven, hob, garage etc.

I guess I need to read up and understand the full extent of the applicable differences between 16th ed and 17th. Are there any recommendations for a good book to cover the subject that doesn't me to call in an electrician at every other turn?

There seems to be quite an emphasis on testing circuits after installation, but I'm unsure whether this is necessary where I know my workmanship is good and the circuits are simple, and there is simple continuity testing I can do with a multimeter. Anyway I'm keen to do things properly so I'd be interested to hear what people's views are on this and assuming I really do need to do proper testing (I think I do) how can I do this without forking out hundreds for testing kit?

Finally what's the current state of play with Part P and building control? I've had a good look through recent posts and there doesn't seem to be much discussion on the subject so I'm not sure where the DIY'er currently stands with this? My local authority is Leeds if anyone's familiar with their processes...

Apologies for the long post, and thanks in advance...

[Owain]

You don't have any un-RCD'd circuits. The CU is split into two halves, and each half has an RCD. The idea is the whole house doesn't go off when an RCD trips. It's still a bit of an kludge compared with having individual RCBOs (combined MCB + RCD) for each individual circuit.

Try to split the lighting circuits over the 2 RCDs so you don't lose all lights at once.

A radial for each room and you will need either a large CU or have some rooms without sockets! And you have a choice of using 2.5mm cable and only having 20A on a circuit, or having to use 4mm cable to get

32A on a circuit.

Hob will usually require a dedicated cooker circuit. Single oven might be less than 13A, but better placed on a cooker circuit IMO.

Not *much* difference apart from RCDing everything unless you use a limited range of cable methods, and if you do RCD everything you no longer need equipotential bonding in bathrooms. You still do need main equipotential bonding though.

A multimeter will not test insulation or continuity to the required standard, but you can hire a 17th edition tester for a week/weekend fairly cheaply (~=A3100)

If you are DIYing it you are supposed to make a building regs application for the work. The local authority is then supposed to do any inspection and testing they want to do, and not charge you extra for this. However, not all authorities are as co-operative as others.

Owain

[Dave Liquorice]

Might be wise to have the downstairs lights fed via the RCD that protects the upstairs ring and vice versa. So if some one does do somthing to trip the RCD they don't get plunged into darkness as well. Of course some one somewhere else does... 6 of one half a dozen of the other. RCBO's avoid this...

[Andrew Gabriel]

If you are doing this yourself, look at using some of the money you're saving to provide RCBO's rather than the 17th ed kludge.

[mick]

If you check out part P then you'll find that there is very little that you *can* legally do now without being registered. You can't install any new circuits. You can't modify or change the CU. You *can* change a socket - even from single to double! :-) You can't change or install a light fitting in a shower. ...and lots of other stuff.

You're right. There is a lot of emphasis on testing. In order to get a test certificate this has to be carried out - and you are very unlikely to find any 'leccy who will test and issue an Electrical Installation Certificate (the one that you need) where someone else has done the work. Nowadays you should really have that certificate if you come to sell the house. :-(

Without the right (calibrated) gear there is no way that you can test an installation and issue a test certificate. Even the test certs are serial numbered and traceable back to the issuer so you can't scrounge a blank. They won't photocopy either! (Just in case anyone wonders how I know this, I type up test certs for an electrical contracting firm as part of my job.)

[Mike Harrison]

If you are using all new parts/cable and are competent at wiring, the probablility of a fault that would only be detectable by a 'proper' tester is negligible.

For a makeshift insulation test, a low-range AC current meter across an open breaker should show up anything serious.. Continuity test at high currents could also be improvised with a little imagination.

[JimK]

be creative - do most of it yourself but e.g. "forget" the main equipot. bonding. or someat.

Then play dumb, get a sparks to quote - say you've recently bought it and you'd like a full Perodic Inspection (with tests etc) doing please.....

cheers JimK

[Owain]

but you can, legally, if you put in a Building Regulations application.

But the Installation and Test certificate format is (was) in the back of the Regs and AFAIK nothing to stop someone typing up their own.

Owain

[Tim W]

Mike Harrison wibbled on Monday 04 January 2010 09:47

Yes, but don't read this as "no need to test at all".

First ring circuit I put in 2 weeks ago showed up a broken neutral on the end-end test. This is with 35mm back boxes, all new parts, care when assembling etc. I reckon it was the screw bit the cable too hard (my personal faults is I tend to over tighten rather than under tighten things). Just weakened it enough to cause the wire to snap when plate replaced.

So testing is important. But you could have found that with a multimeter. Ditto a multimeter will find functional wiring errors on the figure-8 tests, but it will not tell you if you have a bad connection or have damaged the insulation. You'd probably get away without an IR test but I strongly rate having a loop impedance meter.

It's also a good idea to prove the RCDs are in spec, though one could hash this up with a carefully chosen resistor if you're prepared to not test the trip time aspect.

But if you are doing a new installation, I think it is well worth the money to aquire a second hand multifunction tester or single function meters) or borrow/rent one for a day.

No argument there.

[Tim W]

mick wibbled on Monday 04 January 2010 09:43

Not correct. You can do it all under Building Control.

The electrician will be more than happy to do a PIR though (and charge for it) and a PIR is the usual mechanism by which Building Control validate your work.

Not fully correct. You use IEE/IET modal forms freely downloadable from from

The serial numbered ones you are thinking of are the ones on NICEIC (et al) pads.

But yes, you "properly" complete an EIC (that Building Control will believe) you need calibrated test instruments.

Cheers

Tim

[Andrew Gabriel]

Also, this is the first time you've used a new roll of cable. Although I've never had a faulty roll, I would not simply assume there are never any conductor breaks.

Last few complete ring circuits I've installed, I managed to get the cable and sockets installed without a single cut in the conductors. That does reduce the chance of an open-circuit ring.

Another simple check you can do - using something like a 2kW heater or 3kW kettle, check the voltage drop at one or two places around the ring as you switch it on and off, and make sure it's roughly what you expect.

I made my own 20+ years ago. IME, RCD trip is so instant (i.e. vastly shorter than the allowed times) that you have no difficulty seeing this without time measuring equipment. (One day, I must add the DC test to it though;-)

Yikes. May well show up as a test meter blowing up in your face if there's a fault, or you accidentally touch the probe on the wrong place..

[Tim W]

Andrew Gabriel wibbled on Monday 04 January 2010 11:10

That's certainly bomb proof :)

Sadly, for me it would mean feeding 20-25m of cable effectively through every conduit drop and up again as all mine come down from the ceiling.

I *do* wish they'd use captive terminals in accessory plates though. In this day and age, one *really* should not have to be worrying about whether the

3rd CPC went up the side of the screw and is about to fall out...

[Andy Dingley]

Yes you can, you just can't sign them off.

There's still the BCO route, and if you're looking at a full re-wire, that can make sense.

[Tim W]

Andy Dingley wibbled on Monday 04 January 2010 12:36

It can make enormous sense. If a pro rewire is 3-5k and you can do a very nice job with

[Nutkey]

I created a new kitchen ring and changed the main, garage, and shed CU. The BCO accepted my EIC (and was pretty happy to, his first question was "can you test it for us"). I bought a megger and did it all properly.

I priced it for the purposes of the BNA, but underestimated the number of hours quite substantially :) I learned lots though...

45 quid I think, and he came to my house.

The guy who gave me the most hassle was from Siemens. I booked a disconnect and reconnect for the mains as I didn't have an isolating switch. So I screwed an isolator to the wall ran some tails out of it, and when he turned up wondering why he had to do a disconnect and reconnect *at the same time* I explained I wanted the old tails disconnected and the new ones connected.

He didn't like that at all. He did it, but he came back at the end of the day when I had things more or less done. He wanted to make sure I had N and L the right way round, which he tested with a socket tester... It beeped, he was happy.

[Tim W]

Nutkey wibbled on Monday 04 January 2010 16:17

EDF did that to me too - only he waved a voltstick over the wires in the CU. Looks like arse-covering to me...

The trick for me was (as I had the main fuse out all day) to make an exceedingly neat job of the wires in the meter box (including the isolator I wasn't supposed to put there- ha) and I ran the tails into the CU in Kopex pliable plastic 32mm conduit (seemed the best way to protect them going up the soffit and over the wall leafs) with nice chunky IP65 glands into the meter box.

After that he stopped complaining and became very helpful...

[js.b1]

Read SI 2006 on ODPM. There are notifiable & non-notifiable works.

Notifiable works...

- New final circuit

- New SWA to shed or garage

- Extending final circuit in kitchen & bathroom

- Changing a CU re enclosure and protective devices (CPD)

- etc

NON-Notifiable...

- Maintenance operations even in special locations or connected with them

- Extending any circuit not in a special location (extending power circuits, light circuits)

- Replacing a RCD, RCBO (eg, no trip on test button)

- Replacing a shower

- Replacing a SWA cable to a shed

- Replacing any circuit cable (circuit defined as supplied by a CPD)

- Changing an enclosure (including a CU enclosure, but not all CPD)

- Extending a porch, shed, garage circuit is not a special location

- etc

So a "rewire" may not require much notification at all. Probably the CU, but unless you are gutting the house you can do bit by bit - 20A radials per room are a good thing here because you can do a room at a time re mess / time / cost.

MK Grid is fiddly to work with - but useful where you have a space problem such as 300mm from sink on one side, wall on another side, and

4 switches or whatever to fit in.

Hall lights on dedicated or downstairs light circuit is a good idea - most people put them on the upstairs circuit so when a (usually) incandescent bulb pops the stairs and upstairs are plunged into darkness.

Dedicated smoke alarm circuit, with heat alarm for kitchen.

Whatever you do, plan everything now if it is not easy to add stuff later (solid floors, can't access ceilings re sprawling outhouses and extensions, floors & ceilings on different levels). Alternatively leave a few bits of conduit in place to ease replacement. Use a large CU and put spare 20A radial circuits to a 20A DP switch which you can extend later should the need arise :-)

[js.b1]

It is very common, and down to the wiring accessory.

- RCBO & MCB use a T-bar off a screw to clamp multiple cores

- Wiring accessories use a bare screw and hope the cores grip equally, don't stack, don't dislodge

The most common damage is 1mm lighting being squashed to nothing, bit of flexion putting it back and it breaks (1.5mm FTE doesn't help much as the CPC is 1mm also). This is one area where T-bar terminals would help.

I have an SFCU irritatingly located close to the ceiling & close to a wall which makes access difficult. The SFCU goes on to supply a Class-1 outside light and a temporary outside socket, so integrity of the earth is rather important (it does have RCBO protection). This morning at 2:21am, with the wall open to repair plaster around an architrave, I decided to change the backbox to 47mm from 35mm and use a 5-way Wago Lever connector to link the earths - and a 6491X earth to the SFCU. That way I know the earth remains perfect rather than one coming out, twisted-together breaking etc.

The most important tester is an RCD tester. You can get decent ones for about =A3125 on Ebay occasionally (whoever electrical factor relabelled megger RCDT320), or used for less/more depending on spec.

An IR (Insulation Resistance) tester is good, but over-rated. Many types of cable deteriorate at the ends - TRS (& lead covered TRS) suffers insulation falling off by rotting, Polyethylene suffers severe insulation cracking if overheated, butyl suffers UV degradation, post- WWII PVC suffering green goo can cause tracking at exposed ends. In all those cases an IR test will often say "fine" so someone walks away, in the first two of those cases a fire is quite possible particularly if rewireable fuses provide OC protection.

Continuity & Polarity are critical - especially polarity w.r.t. lighting with ES lamp holders. RCD testers usually check polarity (they will not do a test on a LN reversal for starters, not uncommon if something wired in low light re BL/BR colour rendering).

A reminder is to check smoke alarm are all wired correctly because otherwise the cost is a whole set of new ones (=A3200+).

[Brett Jackson]

If I were to use RCBO's for the lighting circuits, would I still be required to have 2 RCD's? It would seem to me that in using RCBO's I would have exceeded the original requirement, albeit in a slightly different manner to the accepted norm. I'm thinking that I can buy a

17th ed CU, use RCBO's as explained then use the second RCD in the garage...

I'm looking at at least a 15 way CU, or maybe even 20+. The radials would be 2.5mm T&E protected by 16 amp MCB's as I have no appliances outside the kitchen that come close to needing even 13 amps.

Oven and hob will be on their own MCB's

[ARWadsworth]

The words "17th editon CU" actually means "the basic minimum compliance of the 17th edition regs".

I am still not sure that a dual RCD CU meets that requirement where mains smoke alarms are fitted.

I now offer customers a choice of consumer units and explain the options and price differences.

Adam