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Rewiring questions. (Read 7889 times)
david daytona
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Rewiring questions.
Mar 5th, 2010, 9:28pm
 
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I'm about to do a rewire on a house that's about 80 years old (all legit, having Building Control's leccy inspecting it Smiley ) and I wasn't certain on this:

1) Is it necessary (or just optional) to fit a mains powered smoke alarm(s)?

2) I understand that as it's a rewire the current positions of the wall outlet sockets can be used (too low for a new build), is this correct?

3) Max/min height of consumer unit from the floor and from where would it be measured (top/bottom/trip switches)? As it's a rewire, would they apply? Could I simply position the new one in the current position if it falls outside the suggested placing in the latest regs? The consumer unit is at about chest level under the stairs, immediately behind the door, so easy to reach.



There maybe additional questions later. Grin
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The_Trician
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Re: Rewiring questions.
Reply #1 - Mar 5th, 2010, 10:59pm
 


Quote:
1) Is it necessary (or just optional) to fit a mains powered smoke alarm(s)?


No mention of it as a requirement of the wiring regulations.
Building regs might be different, but since it's a rewire & not a new-build, I suspect it is merely a recommendation rather than an actual requirement.

Quote:
2) I understand that as it's a rewire the current positions of the wall outlet sockets can be used (too low for a new build), is this correct?


Yes, that is correct - put them where you like within common sense reasoning!

Quote:
3) Max/min height of consumer unit from the floor and from where would it be measured (top/bottom/trip switches)? As it's a rewire, would they apply? Could I simply position the new one in the current position if it falls outside the suggested placing in the latest regs? The consumer unit is at about chest level under the stairs, immediately behind the door, so easy to reach.


As per your second question.
Joined-up DuffGov thinking changed this and suggested that consumer units in new builds be placed in a position such that it is accessible to someone reaching from a wheelchair. What they didn't think off was that this would also make the consumer unit accessible to the curious fingers of a small child, but hey, That's NuLabour Nanny for you!

Basically, fit it where the cover can easily be opened or removed for future upgrades/additional ccts/ repairs & testing. Don't box the damned thing in!

Ensure that it is not placed in the proximity of things like pipework which may leak onto it, or might make it difficult for someone from another trade to carry out any work which may be required.

Once again common sense is the route to follow. Don't listen to Nanny, use your noddle!

TT
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david daytona
Re: Rewiring questions.
Reply #2 - Mar 6th, 2010, 7:42am
 
Many thanks.  Smiley
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Re: Rewiring questions.
Reply #3 - Mar 6th, 2010, 8:31am
 
I'd fit mains powered smoke alarms anyway if it's easy. The (backup)batteries seem to last longer.
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Re: Rewiring questions.
Reply #4 - Mar 6th, 2010, 9:28am
 
I'd agree with the guys.

I'd also instal two mains powered alarms - interconnected. You might as well do it as you're going to be hacking into walls etc, I'm assuming.  You need a different types for the kitchen and upstairs landing...which are the recommended placings in a typically sized house.

Don't expect Building Control to send out an electrician.  When I did my rewire the only thing they asked was whether I was using a 17th edition CU.  Don't forget to ask them to come and inspect the cable runs at first fix stage....although again don't be surprised if the bloke who turns up knows less than you.
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Re: Rewiring questions.
Reply #5 - Mar 6th, 2010, 9:45am
 
Heat in the kitchen, smoke within 3m of every bedroom door and 7m of every habitable room.  (need to double check that).

I would install them for the cost of little bit of 3c+e cable and a few detectors.  The Aico Easyfits are compact, neat, easy to fit and surprisingly well priced.
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Re: Rewiring questions.
Reply #6 - Mar 6th, 2010, 9:42pm
 
Thanks for all the replies. Smiley

Round 2:

1) I rewired my last house (around 5 years ago) and in the kitchen I put DP switches for the fridge and freezer (under worktop models) and washing machine above the worktop, these switched the sockets below the worktop for the 3 machines. At the time a local electrician told me to do it this way as it enabled the machines to be turned on/off without have to drag the machines out. He said I was required to do this. Is this the case? It seemed reasonable to me, but I don't know if it is compulsory.

2) I have seen cooker sockets fitted to both the wall and to the carcass of the cooker housing, is this acceptable practice or a lazy kitchen fitter?

3) Am I right in deciphering the 17th regs regarding upstairs hallway lighting in that they should be on the downstairs lighting circuit so that if the upstairs lighting circuit RCD trips you're not left totally in the dark?

4) Earthing, I have read so many conflicting opinions I don't know what is right and wrong now.
a) Do you still form a 'daisy chain' of earth cables between all the boiler pipes?
b) Do you still need to bring an earth cable to the radiators and any metal sinks? If so what cable sizes should be used. Presumably water and gas pipes still have to have earth cables brought to them and again what size cable should they be. (It is a small 2 bedroom house, to give you an idea of the likely power consumption, not sure what fuse is in the service head).

5) Cable sizes for standard electric single oven and electric shower (<10kw) 6mm or 10mm to each? Any special earthing requirements for the shower (it be on an RCD naturally)?

Ta. Smiley
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Re: Rewiring questions.
Reply #7 - Mar 7th, 2010, 1:00am
 
Quote:
1) I rewired my last house (around 5 years ago) and in the kitchen I put DP switches for the fridge and freezer (under worktop models) and washing machine above the worktop, these switched the sockets below the worktop for the 3 machines. At the time a local electrician told me to do it this way as it enabled the machines to be turned on/off without have to drag the machines out. He said I was required to do this. Is this the case? It seemed reasonable to me, but I don't know if it is compulsory.


It's a confusing area!

a) It seems a good idea.

b) Rumour has it that any kitchen appliance engineer will refuse to work on an appliance which is not capable of being 'isolated'.

Now, whether you use a switched single socket and the appliance plug to isolate, or you use a socket which can be switched 'off' via a double pole 20A switch is a vague area. The regs just call for a satisfactory means of isolation.

c) from a technical point of view, a Ring final cct is protected by a 32A mcb. 2.5mm twin and earth is rated at around 30A when configured as such. Trouble is; the dp switch is only rated at 20A. Not only this, but 2.5 is only rated at around 21A when wired as a radial cct, or in this case a radial spur off a ring final. Now the load (appliance) most likely won't take 20A on the switched side of the switch, but the live side which is connected as part of the ring. Clarification has regularly been sought from people like MK as to what their dp grid switches are actually rated at, but not a single manufacturer has been forthcoming with this information.

In practise, you'll most likely have no problems, and it is a common method of switching and isolating under-worktop and built-in kitchen appliances, but for a definitive answer as to whether or not it fully complies with the regs, please let us know if you find one!

Quote:
2) I have seen cooker sockets fitted to both the wall and to the carcass of the cooker housing, is this acceptable practice or a lazy kitchen fitter?


Good practise and workmanship is that any electrical accessory serving as part of the fixed wiring in an installation means that the accessory should be affixed to part of the fabric of the building.

Now we can become all lawyer-like and argue the toss as to whether or not a fitted kitchen can ever be truly defined as part of the fixed fabric of the building.

For me, the fixed fabric bit starts at the finished plastered face of a wall period. Anything else doesn't count - but hey - that's just my view.

Quote:
3) Am I right in deciphering the 17th regs regarding upstairs hallway lighting in that they should be on the downstairs lighting circuit so that if the upstairs lighting circuit RCD trips you're not left totally in the dark?


Not sure if it's a specifically mentioned reg, but there is a reg which states that a cct should be designed in such a way that it does not pose a risk or inconvenience to the user, so I would say yes.

Quote:
4) Earthing, I have read so many conflicting opinions I don't know what is right and wrong now.
a) Do you still form a 'daisy chain' of earth cables between all the boiler pipes?
b) Do you still need to bring an earth cable to the radiators and any metal sinks? If so what cable sizes should be used. Presumably water and gas pipes still have to have earth cables brought to them and again what size cable should they be. (It is a small 2 bedroom house, to give you an idea of the likely power consumption, not sure what fuse is in the service head).


Right, I get the impression that you are confusing earthing with bonding.

Earthing first.

We won't go into the technicalities of supply characteristics since you haven't given enough information.

So here's the form for a PME supply only.

Note: if the supply is TNS or TT, then the following cables sizes will comply generously!

The main earthing conductor shall not be less than half the size of the live conductor, so for 25mm L&N tails from the meter, you would choose a 16mm main earthing conductor.

The main equipotential bonding conductors to the main gas and water intakes should each be 10.00mm. The bonding connections to both gas and water should be made to the pipework within 600mm of where the main supply pipes enter the building and before any pipe branches.

Daisy chaining at the boiler. Sometimes needed, sometimes not needed, but a belt & braces approach.
This may happen if it is convenient to bond everything in one place.
A boiler usually has a gas supply and a water supply.
The boiler is usually a Class 1 appliance, so the (cpc) earth wire in the 3 core flex which supplies the boiler is also effectively a bonding conductor. the flow & return to the radiators can be bonded together here too. It doesn't do any harm, but make sure that the main 10mm equipotential bonding conductors, if present at the boiler pipework, are also present at the mains water and gas pipe intakes first.

Quote:
5) Cable sizes for standard electric single oven and electric shower (<10kw) 6mm or 10mm to each? Any special earthing requirements for the shower (it be on an RCD naturally)?


Up to 8KW, 6.00mm is usually fine, so long as it hasn't been run through loft insulation and the like. Above 8KW and you move to 10.00mm or even 16mm if the cable run is through loft insulation or any form of wall insulation.

The shower should be bonded to any exposed metalwork in the bathroom and to any other electrical accessories.
Yes, RCD protection is now required.


I haven't covered everything here because it's silly O:clock in the morning!

TT
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david daytona
Re: Rewiring questions.
Reply #8 - Mar 7th, 2010, 8:03am
 
Thanks again, do you not sleep? Grin
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Re: Rewiring questions.
Reply #9 - Mar 7th, 2010, 9:18am
 
TT has given excellent advice.

DD...you clearly sound as if you know what you're doing and are coming at this with the right mental outlook!

I myself went through virtually the same set of questions when I refurbished a cottage and rewired it myself.  If you do a search on my username then that might help you find some fleshing out of any answers 'cos we've been there already most like  Grin

re bonding...I was able to gloriously raise two fingers since (a) I had no gas and (b) the incoming water pipe was plastic as was all the plumbing that I put into the house.

I did everything according to the book or as close as one could given the 'grey' areas ...which you've already touched on  eg kitchen carcasses.  When my first fix inspection came, the BC guy turned up and said 'I've come to look at your insulation'..gazing at the Kingspan in the roof.  'Oh no, you're not' says I 'it's a first-fix cabling inspection'.

A look of panic crossed his face. As we walked around and I bullshitted my way about safe areas and trench depths he said 'You know more than I do'...so go figure  Roll Eyes

When it came to the final inspection, as I mentioned earlier, they did not send out an electrician. Their approach is to come out and have a look. If you've got a 17th edition CU then that gets a big tick...quote 'they make our job so much easier'....which is a bit concerning as you could have wired it in bellwire for all they knew.

The only time they send out an electrician is if they think you don't know what you're talking about. The electrician then does a report which goes to BC. BC then tell you what you need to fix.  At no time do you get to see the electricians' report and at no time will you get an electrical test certificate unless you pay for an electrician to do it.

As far as selling the house goes in the future, you might get an antsy buyer/buyers' solicitor who wants an electrical certificate. Your approach to that question is clearly up to you. In my case, bottom line was that the fact that the whole project was signed off by Building Control meant that I was covered.

NB that was for my local BC...yours' might be different. Have you spoken to them?

You have put in a Building Control notice already, haven't you?
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david daytona
Re: Rewiring questions.
Reply #10 - Mar 7th, 2010, 6:45pm
 
Thanks for the advice Londonman, Smiley I've spoken to Building Control last week, just briefly.  I haven't started ripping out the old system yet so tomorrow I am giving them a Building Notice (+£150 Cry ). I plan to start the job during the week. I've got most of the cabling and conduit now, but have to pick up the consumer unit, looking at one of the MK Sentry ones, used them several times over the years so they feel familiar to me.

Wish me luck! Smiley
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Re: Rewiring questions.
Reply #11 - Mar 8th, 2010, 3:48pm
 
Quote:
1) I rewired my last house (around 5 years ago) and in the kitchen I put DP switches for the fridge and freezer (under worktop models) and washing machine above the worktop, these switched the sockets below the worktop for the 3 machines. At the time a local electrician told me to do it this way as it enabled the machines to be turned on/off without have to drag the machines out. He said I was required to do this. Is this the case? It seemed reasonable to me, but I don't know if it is compulsory.


The electrician that did our kitchen said that there needed to be a way to isolate appliances reasonably easily. He said that either meant switches above the work top OR putting the appliance sockets in the back of an adjacent cupboard. The only thing he wouldn't allow was putting appliance sockets behind the appliance or another appliance.

Quote:
5) Cable sizes for standard electric single oven and electric shower (<10kw) 6mm or 10mm to each? Any special earthing requirements for the shower (it be on an RCD naturally)?


Personally I reckon electric showers suck. If you must have one I'd put in the most powerful one you can get provided your electric supply will hack it. The power rating of a shower in kW effectivly determins the flow rate rather than the temperature. The higher the power the more water you get out.
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david daytona
Re: Rewiring questions.
Reply #12 - Mar 9th, 2010, 6:46am
 
I'm not keen on electric showers too, but in this house the central heating system has a fairly low head and I don't want to fit a powered shower as the hot water cylinder is relatively small, to fit a more suitably sized cylinder one is going to be a major head ache due to positioning problems. The old electric shower had a DP switch outside the bathroom, (ugly old thing in the middle of the wall) is it necessary? or just a convenience, obviously it could be disconnected for 'once in a blue moon' maintenance at the consumer unit. Undecided

Something had me stumped today for the answer. As we are obliged to use blue and brown for the live and neutral for the installation, what about the cables between service head/meter and meter/consumer unit they are currently red/black? Presumably they stay as they are (or not)? Huh
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