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Post Time: 09/02/2009 21:47:11 |
elle66
Total Forum Posts: 15 |
Hi there
I'm buying a house which needs complete renovation including rewiring. Have just read the document on rewiring a house and whilst I feel that any competent electrician should be able to read this and then rewire using screened cabling and the radial method, I wondered if anyone has actually had anyone do this kind of work for them. I had three electricians out last week to quote (before I'd seen the article) and whilst a couple of them seemed open to suggestions, they'd never actually done this kind of work before. I'm wondering if it would be better to get an electrician who works on public/commercial buildings as they seem to be used to working with metal conduits?
I desperately want to get this right as my little girl had cancer several years ago and obviously I want to be extra cautious when it comes to her health.
Also, just a query on the cost. I've been told that it will cost about 50% more than a standard rewire so I'm a bit confused to read in the document that the 2007 SAGE report estimates that it would only cost about £20 more.
I'd really appreciate any advice.
Many thanks
Elle |
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Post Time: 10/02/2009 18:25:35 |
alasdairP
Total Forum Posts: 173 |
Elle
You have certainly been doing some careful quality reading to notice these things. It can be very confusing.
(i) The SAGE additional average cost of £20 was for new houses, not for re-wiring. For new builds, it works out less expensive (especially multiple builds on new developments). Also (ii), more importantly, this was just for radial wiring and the RCD to minimise magnetic fields, not for screened cable to reduce the electric electric fields.
Using screened cable about increases the CABLE cost by 3 or 4-fold (which is only a part of the whole cost of all the fittings plus labour). That would probably add a couple of hundred pounds to the cost. More difficult to cost is the fact that few electricians have worked with screened cable and so they greatly increase their estimate of the time needed to do the work. That would probably add more than the extra cost of the cable.
Is using screened cable really important? If I were to have a house re-wired now I would use it, but I haven't bothered to have my existing house rewired using screened cable (too expensive for me for the possible benefit). I have changed the lighting circuits so that the 230 volts goes to the switch before the central room light fittings (it is often/usually wired the other way around) as that means when the light is switched off there are no 230 volt cables winding their way across the ceilings/under the upstairs floorboards. The downstairs lighting wiring is usually the main source of electric fields upstairs.
If you ask them to wire that way (it usually requires more junction boxes - which are cheap), then just doing the radial wiring using ordinary cable would be a much cheaper option. Also, ask them to try to keep most cables along the room edges and not run across the middle of rooms greatly helps to minimise electric fields. Also, try not to have electric sockets behind beds. About a metre to either side of likely bed positions is probably best.
If you do still go for screened cable, then Prysmian FP-200 Gold cable is OK to use. That is cheaper than the top of the range BS 8436 cables that are "officially" recommended, but is just as good at screening the electric fields. It is still about 3-fold more expensive than standard twin and Earth PVC cable.
Please feel free to ask more questions if I haven't answered all your points.
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Post Time: 10/02/2009 19:05:30 |
elle66
Total Forum Posts: 15 |
Thanks Alasdair,these suggestions are really, really useful - I found that the hardest part was conveying my requirements to the electricians but I can go back to them with confidence now. I've also had a very quick look at the document about safe lighting so I probably will come back to you later with a few questions on this.
Many thanks
Elle |
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Post Time: 12/02/2009 10:13:31 |
neuroki
Total Forum Posts: 13 |
Alasdair: can you explain a little more about how you have wired the lighting circuits ie "the 230V goes to the switch before the central light fitting". Are you using a double pole switch or are you just putting the junction boxes somewhere out of the way like at the side of the room or chased into the wall?? or using the light switches as junction boxes??
Most if not all electricians should have experience with working with pyro (micc) cable. Although again it will be expensive, is it not also an option to surface re-wire a house in pyro for example - although admittedly it may not be aesthetically pleasing! Depending on the house it can be tastefully done (so long as the sleeving is not used). |
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Post Time: 12/02/2009 21:31:39 |
alasdairP
Total Forum Posts: 173 |
Pyro is excellent but very expensive. Much more so than screened cable.
I should really do a diagram, but can't just here at present. So, here is my explanation.
Normally (in the UK) the lighting circuit main feed cable goes around the house zig-zag to reach every light fitting. Most are still in the centre of rooms. The light fitting backplate has a 4-wire screw terminal block, so the cable is looped from light to light using three of the connections. Another twin (phase and neutral) and Earth cable goes to the light switch (or a special 4-wire cable if there are two switches for the same light) - this cable carries the phase (230 volts) out and the switched line back to the bulb. When "off", there is still 230 volts to the light fitting and also a long 230 run to the switch. These greatly increase the electric fields in a house.
The better way, to minimise electric fields, is to run the feed around the walls (with the power cables) and to use a junction box to connect the drop cable to the switch and the cable to the light. This way reduces the lengths of cables with 230 volts on when the lights are switched off. It is surprising just how much using this technique can reduce the electric fields, especially in bedrooms on the floor above. So, at night, there are no underfloor cables to the centre of the room with 230 volts on them.
I hope you can follow my explanation.
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Post Time: 13/02/2009 09:07:34 |
neuroki
Total Forum Posts: 13 |
Yes I think I follow that. Although there will be a live cable to the switch at all times, it's only when you switch the light on that you will produce an electric field (via the switch wire)that will run into the middle of the room.
Where would you put the junction box? I suspect that it still must be under the floor boards (in which case the wire to the switch will not be a "drop cable" but a "rising cable" )and the switch wire and neutral from the junction box still needs to run up the wall and across to the ceiling.
Such a shame that you can't do a workshop for electricians or DIY ers... hint, hint!!! |
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Post Time: 14/02/2009 18:13:58 |
alasdairP
Total Forum Posts: 173 |
Yes, you have followed it correctly.
Generally, lighting wiring runs above the ceiling, so the cables usually drop down from above. If it comes up from below then you would need to cable the whole height of the wall (from below to supply the power and to the ceiling to supply the light). Often one junction box can supply at least two switches in adjoining rooms - depending on the building construction.
We have often thought about seminars. It is difficult to do them cost effectively. Suitable venues are costly and finding dates that a reasonable number of people could attend is surprisingly difficult. When the Ministers' respond to SAGE (shortly, hopefully), then there may be some support for training/ information giving meetings as there is quite a lot of support for "better practical information". One possibility is to write a more practical guide, but these things take a lot of time and effort and we have to pay our bills so it isn't a realistic priority for us.
Don't forget about "demand switches" (EMFields sell one). They are quite expensive, but they do disconnect the 230v AC when everything on the circuit is turned off (and automatically re-connect when someone turns a switch on). They can be a more cost effective way (c.f. re-wiring) on achieving significantly lower electric fields upstairs at night when installed on the lighting circuit(s).
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Post Time: 16/02/2009 11:11:08 |
neuroki
Total Forum Posts: 13 |
Yes I've seen the "demand switches". They are a good idea and politically correct re: saving energy!
My only reservation about them is that under Part P of the building regs, it is notify-able work to fit them in the consumer unit. Also I suspect it may require installing a new consumer unit if there are not any spare ways left in the old one, which will make it much more expensive. Still, like you say a lot cheaper then re-wiring the entire house.
Is there any way of connecting the "demand switch" outside of the distribution board? I suspect that will still fall within the scope of Part P, but should save money on not having to buy and install a new distribution board! |
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Post Time: 16/02/2009 14:53:40 |
elle66
Total Forum Posts: 15 |
Hi Alasdair, I'm going back to the electricians with my exact specifications and I'd just like to run it by you first to make sure I'm on the right track.
We've decided to go for the recommendations in your House Electrical Installations and EMF's document (Page 17, section 3.3 - from the SAGE report). In addition to this we'll also make sure it's a metal consumer unit (which is located high up on the garage wall underneath my child's bedroom - should I move this towards the bottom of the wall?). And regards the wiring, am I right in thinking that screened cabling is INSTEAD OF metal conduits?
I think these recommendations mean that it will be less complicated to do, i.e. cables can be run anywhere, not just around the edges of the rooms, the distance from the bed positions won't matter and the lighting wiring that you and neuroki have been discussing won't be applicable?
I also have some queries with regards to lighting. My kid's bedrooms are on top of the garage/kitchen where I plan to install 2 spotlight ceiling bars in each. Each bar contains 4 GU10 halogen lights which I will substitute with Enviro-Light LED GU10 3 Watt 220-240V. Will this have the desired effect of cutting out the magnetic emissions in the bedrooms above? Also is it ok to have LED wall lights wired to either side/above my beds?
Look forward to hearing from you.
Many thanks, Elle |
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Post Time: 02/03/2009 18:03:25 |
alasdairP
Total Forum Posts: 173 |
Now answered on your newer posting. |
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Post Time: 06/01/2010 16:23:18 |
krishna
Total Forum Posts: 9 |
It took me several goes to find an electrician willing to take on board what I was asking for. The house needed a complete rewire anyway. So following advice from here, I got him to use FP200, run cables round the edge of rooms, looped ring or radials for the power points. He thought I was mad but at least he understood what I was asking for and more than happy to oblige. Charge me an extra £200 for the cables. Total cost £2500. That was about 18 months ago. |
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Post Time: 06/01/2010 21:51:24 |
elle66
Total Forum Posts: 15 |
Sounds like you got a good deal Krishna. I did get the work done but ended up having to use an electrical contracting company. The sting in the tail though was that it cost £6k to rewire a 4 bed semi! |
