My Complete DIY Rewire

[JohnW2]

For a lighting 6A radial using 1.5 mm² you will see it's around 44 meters.

It looks like I've got over 44m, presumably simply sticking in 2.5mm should do the trick?

Eric's figure of 44m presumably related to the guidance as regards maximum voltage drop for a lighting circuit (3% of 230V), assuming the circuit is fully loaded to its 6A maximum (1,380W total lighting). From the point of view of earth fault loop impedance (which is the safety issue) a 6A 1.5 mm² circuit could be over 170m long, even with a TN-S earthing system.

If you use energy saving and/or LED lamps, your total load will probably only be a fraction of that 6A/1,380W maximum, so (although some here will probably object!) you could probably argue that (even if one 'believes in the guideline VD limits') it is not appropriate/necessary to ensure that the VD does not rise to more than 3% with a hypothetical load much higher than you will be utilising. I can't say that I've ever seen a domestic lighting circuit using 2.5 mm² cable - and there might be an issue dealing with that size cable in some lighting accessories. However, since this is a potentially contentious issue, you would certainly be advised to discuss it with the LABC before you did anything, if you were dealing with them yourself.

More than 44m for a lighting circuit sounds an awful lot, particularly given that you are presumably going to have two or more lighting circuits. Is it an exceptionally large house?

Kind Regards, John

 

[Risteard]

Yes you can have two circuits in one room. It is only when using 3 phase when this becomes a problem.

There is no prohibition on having two/three different phases within one room.

 

[PreferNotToDieOrBurn]

The more I read, the more I'm convinced that you are not yet competent to be tackling a complete rewire.

I feel the same way, hence seeking advice on any points I'm not sure on.

Everyone: "I think you've falling in a hole PreferNotToDieOrBurn"
Me: "Yes I'm in a hole, but I'm the only one here, can you offer some advice?"

That's basically the reality of it. It's definitely not a perfect situation, I'm fully aware of that, I'm now having to make the best of it.

The below might seem like a cowboy putting on his hat, but consider a man with no money and a seriously dangerous electrical system who needs a solution he can't afford...

I may as well admit that it's highly likely I won't be complying with the proper process/procedure and will probably end up not notifying the authorities and then manipulating some form of testing and test certificate at the end of it. (ie. a periodic inspection and testing certificate, or a cert for replacing a CU)

If I stick to safe zones, and if the CU is fully RCD'ed etc, then I'm confident the wiring will be safe and I don't believe I can afford the risk of having to afford the local authority outsourcing testing and billing me for it.

If I keep it simple, ie:

2.5mm ring mains
1.5mm radial lighting circuits
Everything buried in the wall, in safe zones
Get a leccy to update the consumer unit and test

Then I feel the risks are very low.

FYI the kitchen ring main is already done (yup, I did it, out of neccessity), the cooker cable was already installed and is up to spec/regs and is safe, and the shower circuit was installed and certified by a leccy. So the high risk areas are already sorted.

So please guys, I appreciate my approach may not be ideal but if I had options I wouldn't be here. Please can we focus on making the best of a bad situation rather than pointing out the situation is bad.

Honestly I'm very very grateful for your help and I'm wanting to do this with minimal possible risk.

 

[ban-all-sheds]

Eric's figure of 44m presumably related to the guidance as regards maximum voltage drop for a lighting circuit (3% of 230V), assuming the circuit is fully loaded to its 6A maximum (1,380W total lighting).

And even if a lighting circuit is so loaded, the load is not all at the end of it.

Is it an exceptionally large house?

Doesn't look it.

Untitled

• PreferNotToDieOrBurn
• 24 Jan 2015
• 2

Untitled

• PreferNotToDieOrBurn
• 24 Jan 2015
• 2

 

[ban-all-sheds]

The more I read, the more I'm convinced that you are not yet competent to be tackling a complete rewire.

I feel the same way, hence seeking advice on any points I'm not sure on.

Indeed, but you've already started the work, and seem to think that having asked a few questions here about things you're not clear on you can press on, presumably thinking that if you encounter anything else you're not sure about you'll ask abut that at the time.

That is not the right way to go about it, and not having enough money does not make it so.

The thing is, rewiring a house and installing a new CUs etc is not a trivial job, and I can assure you that it involves knowing far more than you think it does.

Asking questions here can be a useful part of a learning process, but they are not a substitute for proper structured studying. The key term there is "learning process" - you cannot learn all the things you need to know just by asking questions here. It isn't structured enough - it won't provide you with a way to progress where each step builds on what you learned before.

You can't carry out a job of this magnitude by asking whatever random questions happen to occur to you. You've already shown that you have some dodgy misconceptions - what if you get something wrong because you have no idea your knowledge is wrong? What if you miss something because you simply have no idea it even exists, and just don't realise you don't know it?

 

[PreferNotToDieOrBurn]

From the point of view of earth fault loop impedance (which is the safety issue) a 6A 1.5 mm² circuit could be over 170m long, even with a TN-S earthing system.

I can't say that I've ever seen a domestic lighting circuit using 2.5 mm² cable - and there might be an issue dealing with that size cable in some lighting accessories.

More than 44m for a lighting circuit sounds an awful lot, particularly given that you are presumably going to have two or more lighting circuits. Is it an exceptionally large house?

Kind Regards, John

Thank you John for your very helpful reply. I'm aware that maximum runs is based on voltage drop I just wasn't sure if regulations stipulate the maximum run length should be based on the fuse amperage, or on the expected load. I would assume it's the fuse I need to calculate for. But then if the RCD is less than 6A I seem to recall it can be prone to tripping extremely easily, I'm not sure where I read that, have I understood this correctly?

It's only a 100sqm house however the layout is long, and the cables need to go up before they can come down which adds a lot of length to the runs (I've designed it with two lighting circuits)

Are there any other options to boost the run length for a lighting circuit? ie. running a 2.5mm backbone cable and then running spurs off it for each light? ala: https://www.dlsweb.rmit.edu.au/tool...4diagrams/04lighting/images/loop_at_light.gif

 

[ban-all-sheds]

Why do I get the feeling that you are just never going to accept the fact that you are not competent to do this, and will continue to believe that lack of funds means that it's OK for you to press on, and will continue to think that you can do it by asking questions as and when they occur to you?

Sadly, I do know why there are people here who will encourage and attempt to assist you in your folly - it's because they are grossly irresponsible, and, ultimately, they really do not have your best interests at heart, and are deluding themselves when they say that they do.

 

[PreferNotToDieOrBurn]

You've already shown that you have some dodgy misconceptions

Please point them out to me, that's why I'm here.

I'm not afraid to look or sound stupid, in fact I'm openly accepting and embracing that this is inevitable.

I'm also aware of the magnitude of the task at hand and believe me I've been agonising over it for about 6 months. It is a formidable and extremely unpleasant task. But I need to get it done.

I've done some chasing today and so far, so good.

 

[PreferNotToDieOrBurn]

Why do I get the feeling that you are just never going to accept the fact that you are not competent to do this, and will continue to believe that lack of funds means that it's OK for you to press on, and will continue to think that you can do it by asking questions as and when they occur to you?

Because I've pretty much explicitly stated this already. I'm not asking for judgement because believe me I'm already my own biggest critic. I'm asking for help.

The existing electrical system is far more dangerous than anything I could come up with, so even if I have to get the whole thing re-done properly in a couple of years when funds allow, in the interim at least it will be an improvement. Hell, I might not even be too far off the mark.

I'll be posting process photos (and questions) here.

The Makita chaser with no-brand 3000w vacuum are a very very excellent combination, very little dust!

 

[JohnW2]

Eric's figure of 44m presumably related to the guidance as regards maximum voltage drop for a lighting circuit (3% of 230V), assuming the circuit is fully loaded to its 6A maximum (1,380W total lighting).

And even if a lighting circuit is so loaded, the load is not all at the end of it.

Quite so - and, unlike what seems to be someone's convention as regards sockets circuits, I see no reason to assume that even a 'substantial proportion' of the load is at the end of a lighting circuit - it would seem reasonable to assume that the load was distributed reasonably uniformly along the 'used' part of the circuit (i.e. excluding the 'feed' from CU to, say, an upstairs lighting circuit).

Whatever, I need not tell you that I'm personally pretty contemptuous about all this VD business. It seems nonsensical to me to impose a small (and arbitrarily fixed) maximum permitted voltage drop from the origin of an installation when a very much larger degree of variation in voltage is allowed at the origin of the installation!

Kind Regards, John

 

[JohnW2]

Thank you John for your very helpful reply. I'm aware that maximum runs is based on voltage drop I just wasn't sure if regulations stipulate the maximum run length should be based on the fuse amperage, or on the expected load. I would assume it's the fuse I need to calculate for.

I personally think one needs to apply common sense. As BAS has pointed out, even if there is a 6A total load it won't be all at the end. The calculation then becomes much more complicated but, with the lights spread out along the circuit, you could satisfy this (IMO silly) 3% VD 'requirement' with a 1.5mm² circuit appreciably longer than 44m. How long do you envisage the longest one will actually be?

Are there any other options to boost the run length for a lighting circuit? ie. running a 2.5mm backbone cable and then running spurs off it for each light?

Although this might result in me attracting some flak, I really don't think you should worry, or even consider almost unprecedented and complicated arrangements like that. Unless the circuit is ludicrously long (say approaching 100m), I think you should simply plan to wire it all with 1.5mm² cable in the usual way - as I said, that's the largest you'll see used for a lighting circuit in any normal domestic installation, and a good few use 1mm². One would hope that no 'inspecting electrician' would be expecting to see larger than 1.5mm² cable.

Kind Regards, John

 

[flameport]

Are there any other options to boost the run length for a lighting circuit? ie. running a 2.5mm backbone cable and then running spurs off it for each light?

Totally unnecessary, and would make installation very difficult if not impossible.

You do not need 2.5mm cable. Or 1.5mm cable. 1.0mm will be fine.
The length limit is nowhere near 44m.

Ring circuits for sockets are not needed either, they just add significant extra work when testing.

 

[PreferNotToDieOrBurn]

How long do you envisage the longest one will actually be?

The calculations I did for purchasing cable look like 58m, however that's with a lot of extra meters added here and there, so it sounds to me like I'll be absolutely fine with 1.5mm

The lights are fairly evenly spaced over the length of the run.

 

[JohnW2]

Totally unnecessary, and would make installation very difficult if not impossible. ... You do not need 2.5mm cable. Or 1.5mm cable. 1.0mm will be fine. ... The length limit is nowhere near 44m.

Quite so - as I said, with 1.5mm² calbe, one could have 170m+ (and nearly 150m with 1.0mm² cable) as far as EFLI is concerned, and I personally really do think that all this VD business is little more than nonsense.

Kind Regards, John

 

[PreferNotToDieOrBurn]

Todays efforts...

Two chases going loft to ground floor, backboxes installed on the ground floor and even a socket on one of them. Cables going to the loft and second floor but no backboxes/sockets on the second floor yet.

edit: I was also able to do a chase for a light switch where there is already a light switch because the existing installation has the cable going diagonally up and across. Unfortunately this kind of thing is everywhere in the house. It felt very strange chasing from the ceiling down to a light switch while the light was still on, but it was safely done.

Untitled

• PreferNotToDieOrBurn
• 24 Jan 2015
• 2