Large Project

[SGL]

I'm close to completing a large double extension to my property that has almost tripled it's size. The main service has been moved from the centre of the property to a box on the external wall of the integral garage. A local electrician fitted a new 17-way Wylex CU, which is currently (but temporarily) supplying the old circuits. 1 ring, 2 light, 1 Oven etc etc - very basic!
The next stage is to re-wire the entire property and ultimately switch over to the new circuits leaving the existing redundant.
The problem; the property is 22 mtrs wide by 10 mtrs deep and the CU is no longer central. I had a quick walk around with the electrician (mentioned above) and he pointed out that taking a straight run from the CU to the opposite side of the house (and back) will use 44 mtrs of cable -a length he believes would easily double with the loops & drops. His quick opinion was that only 2 rings to support the ground and first floor is not feasible. I asked him how he would approach the problem to which he responded with a lot of uncertainty. He said possibly 4 rings, perhaps an additional CU, heavier cable etc etc...and finished this by saying that he would need to bring along his colleague to do a full survey. His parting shot was; it's not going to be a cheap job!
In summary; I acknowledge his points (since his visit I've read lots about cable lengths and Zs) but I have the uneasy feeling from his comments that it's going to be difficult sorting the good quotes from the "bad" - this is a little more complicated than comparing quotes from bricklayers & roofers! What I'm hoping for is some practical information that will help me to talk informatively to the next guy that quotes.

Before I spoke to the first electrician I put together a wish list of circuits that I wanted based on advise from this forum and other sources; 3x ring for sockets (ground & 1st floor, plus dedicated kitchen ring). 3x lights (Ground & 1st Floor, plus Hall & Landing), Fridge/Freezer, Shower, Hob/Oven, Garage, Outside Lights, Outside Power. All internal circuits (excluding fridge) would be served by RCBO's, Garage & External Lights/Power - MCB's protected by a single RCD. I didn't specify fuse size & cabling as this I believe is beyond my remit so-to-speak!
I showed this to the electrician and he frowned and said; "well it'll have to be a lot more complicated than that!".

So, OK....point taken. It's a big house, but I drive past bigger ones every day! Can anybody advise as to how large re-wires such as this are approached. What boxes should I be looking to tick when I speak to the next guy, what should I listen for, what questions should I ask? No disrespect to the trade, but every stage of the build I've had to deal with people who have attempted to up sell or over state the complexity of the job and this is normally followed by a huge quote. It may well be a very complex task (as the first guy said) but it would be good to get some assurance that my requirements certainly are outside the norm and thus I should be expecting to pay a premium.

My apologies for being cynical, but managing a build from start to finish has taken its toll!

Any advice will be much appreciated.

 

[1john]

Why don't you just make a concise list of what you want in which rooms and then have a list of proposed circuits and present that to electricians as they come to quote, get plenty of quotes and don't reference any previous comments to each electrician, treat each person that quotes as the first person to quote.

 

[flameport]

He said possibly 4 rings, perhaps an additional CU, heavier cable etc etc...and finished this by saying that he would need to bring along his colleague to do a full survey.

Or in other words, they had no idea what they were doing.

While a house 22x10 metres is certainly larger than some, it isn't that big.
32A ring circuits can typically be up to around 100m long in most cases, even with 2.5mm cables. Larger cables will allow much longer lengths.
There is the alternative of radial circuits, and length isn't likely to be a issue with those either - even for lighting circuits in 1.0mm

Multiple consumer units would be a ridiculous option, given that the whole place is being rewired. It isn't the size of the property which matters - it is the expected electrical load. For most rooms (other than the kitchen), the total load is likely to be very small.

Your original plan of 3 rings etc. is certainly a likely solution, although not the only one.

Some suggestions:
- If having RCBOs for the internal circuits, you may as well have the external ones on RCBOs as well - the cost difference will be minimal.
- There is no need to have a fridge or freezer on it's own circuit. Contrary to what some people believe, properly designed and installed installations will trip out approximately never. However, putting the freezer on it's own circuit does mean that if something goes wrong with it, you probably won't notice until it's too late.
- Hall/landing lights on their own circuit isn't necessary. Neither is an upstairs/downstairs split, they could be split left/right or in various other ways. If you are concerned about people falling down stairs in the dark, fit some emergency lighting.
- In your situation, radial circuits will use significantly less cable than rings.

 

[ericmark]

Under the 17th Edition I think it works out at 106 meters of 2.5mm cable max because of volt drop. i.e. A drum. That's a fair bit of cable.

The rules as to using thicker cable for all of the run are OK and with 4mm cable then around 180 meters are allowed however it would be hard to later spur off any sockets if 4mm is used.

As to using thicker cable for part of the run this does not strictly comply with the rules. 433.2.1 says you should fit an overload where a reduction occurs. As long as the device for protection against overload is rated less than all the cable in circuit I can't see a problem but many electricians will go by the big red book.

Sub-Mains are an option and for the kitchen likely a good option it is handy to have sub main in kitchen easy to turn off cooker etc should a fire start.

However every electrician will consider a different approach. Some good and some bad. For example if the fridge/freezer was supplied with Ali-tube cable it would not need RCD protection and would be less likely to fail while on holiday.

Using RBCO's will reduce tripping as would sub-mains with their own RCD so house has three or more RCD's.

The supply type will also alter likely tripping of RCD and it all has to be considered.

So one electrician may want to build you a Roles Royce and another a Mini so price is not only consideration.

Telephone, Lan, Alarm, even door bells can change the price so much and with a quality house no one wants to see Alarm wiring however neat so it can be quite a problem. Especially if you want alarms monitoring and you need that part doing by registered firm. Something like nacoss and unless approved by them getting the alarm monitored can be a pain.

As already suggested you need some quotes. But do be careful and try to see a sample of their work before selecting.

 

[LoveRocket]

Tell your spark to abandon his obsession with ring circuits.

You house may be a bit bigger than average, but it ain't huge - there should be no problems.

What is your earthing arrangement? (TT, TNS or TNC-S)

 

[ricicle]

Tell your spark to abandon his obsession with ring circuits.

Why give advice like that when the OP is already a bit mystified.

To the OP:-
This job will be bread and butter to any competent Electrician. Can you not get some recommendations from friends/family/workmates for a trustworthy, competant sort who gives you confidence with his proposal ?

 

[SGL]

I can't quite believe the time & effort you guys have spent replying. It's refreshing to find people passionate about their subject and also willing to help & advise. These comments are really helpful as it appears my gut feeling was correct; in that there's nothing remarkable or challenging about the size of my house.
I'll proceed as advised and draw up a list of requirements per room, including extras such as alarm, fire protection etc, which frankly I'd completely overlooked! In terms of the type of circuits, your advise underlines the phrase "a little knowledge is dangerous" so I'll leave these decisions to the electrician and simply concentrate on what I need delivered functionally. I also didn't consider checking out the standard of their work before hand. I've done this with all other trades but assumed competency in this respect on the basis that if 'legally' they have to be qualified to do the job, their work will be up to standard. In hindsight that's clearly not the brightest assumption, so looking for recommendations sounds like a good place to start.
Again many thanks for the replies, and to answer the earth question, it was TN-S but was (somehow) changed to TN-C-S (PME) in the course of moving the service.

 

[1john]

Yes, get many quotes, always check references! leave the design side to the electrician, the cheapest quote isnt always the best, although sometimes it can be. If you want MK sockets or what ever then spec that to him / her.

I would imagine that any other electrician would welcome working for someone who has put alot of planning and thaught into a job, but would probibaly prefere that the customer didn't interfere to much on the design specifics.

Good luck with the project, and keep us posted on how you get on finding an electrician, remember, as well as the price and references being right, you also need to be able to get on well with the guy / woman too as you will spend a bit of time together one way or another. You need to feel that you are going to be able to discuss issues with them as you go along should they occur.

 

[securespark]

As the regs advise individual circuits for appliances over 2.5kW, you may want to connect all major appliances in the kitchen and utility rooms via 16A radials. Then for the remaining sockets in the kitchen a 20A radial should suffice.

Two main lighting circuits may well not be enough. It depends on what sort of lighting you are considering. A couple of large rooms chock-full of GU10 downlighters may well need at least one circuit to themselves.

Whatever you do, plan for the future to allow expansion without need for deconstruction!

For example, with a cooker or shower circuit, use 10mm² cable. If you have two electric cooking appliances, put a circuit in for each. This way, you can upgrade appliances in the future without having to worry about the need to upgrade the circuit.

Same with sockets, install them in all places you may need them. If you don't need them that's OK, but how frustrating would it be to suddenly discover you need an extra socket once everything is finished?

Leave extra room for expansion in the CU, too. If cost is not an issue, I would put every circuit that requires RCD protection on RCBO's. If there's a fault, it limits power loss to that circuit, whereas if it were a split-board, you'd lose the whole bank.