Lighting circuit general quiz

[DeadJoe]

I live in a small two bedded house with a single lighting circuit that covers all 8 lights in the building, upstairs and down, and has no earthing. It looks very old - red and black PVC. A couple of questions arise:

1. Is it essential to have separate up and down circuits for lights? The reason I ask is because splitting the circuit is not possible without changing the consumer unit for one with additional breakers. Can I just stick with the one circuit, given the low number of lights (800W, if all 100W bulbs, but actually is now about 250W due to CFLs)?

Upstairs is pretty simple - there are four lights looped with connections in the ceiling roses. The end of the lighting circuit is in bedroom 2.

2. I imagine replacing all the circuit cables with 1.5 T+E running over the top of the loft insulation, and 1.00 to the switches would do it. Does this sound right?

Downstairs is more complicated. There are 4 lights, plus the feed to the upstairs part of the circuit. I haven't fully traced the wires yet (furniture) but I have found a junction box under the floorboards which definitely feeds the upstairs part of the circuit (1) and, judging by the number of wires leading from it, has the switch and power for the kitchen light coming into it (2,3) as well as power coming in (4), which may be via a loop into either the hall or sitting room light, or both. Then there is a fifth 1.0 twin...

3. Does Consumer unit to loop into hallway, then loop into pantry, then loop into sitting room, then junction box to kitchen, and finally upstairs sound like a reasonable plan? It's a longer cable run (the circuit goes to the sitting room light and back on itself to get back to the junction box), but it avoids having more than 4 wires going to the junction box...[/b]

 

[ColJack]

if you're re-wiring the lights throughout, try and not use JB's unless necesary ( such as fancy lights with only L/N/E connections .. )

run 2 seperate circuits, one downstairs, one upstairs and join them at the CU.. this makes it possible and easy to split them should you change the CU at a later date..
this also removes the need for the doubling back from the sitting room..

wire in a logical sequence, don't necesarily follow the same progression..

if you're changing switch drops, put 3C+E in for the landing light, and wire so that the switch upstairs is the one the feed and switch goes to.. ( see 2 way switching in the wiki)..

this will prevent "borrowed" neutrals if / when you decide to upgrade the CU..

 

[DeadJoe]

Good answer - I hadn't thought of creating two circuits joined at the consumer unit. And that would solve so many of the problems, including the kitchen light dilemma (which is a fancy L/N/E) - if I put it at the end of the new downstairs circuit, then I only have the feed and switch cables to deal with, which is a much better proposition...

Does changing the circuit layout upset Part P? I have been assuming that if I replace cable that is 'damaged', bearing in mind the need to add an earth, and looking out for safe zones, and cable capacities, then I would be pretty much in the clear as far as Part P goes. I didn't even consider rethinking the order things are wired in...

Regarding the landing light, you are basically saying that it should be part of the 'upstairs' circuit, with the downstairs switch being connected to the upstairs circuit via the upstairs switch with 3C+E?



[/b][/i]

 

[ColJack]

not entirely sure on the part P front since I've been wiring air conditioners for 5 years and it's been about 9 years since my last house bash.. things have changed...

best to wait and give BAS a nudge in the morning for that one.. he seems to have it nailed down..

as for the landing light, yes put it off the upstairs citcuit.. makes sense since that's where the actual light is..

//www.diynot.com/wiki/electrics:two-way-lighting

 

[flameport]

Don't use 1.5mm - no reason to. 1.0 will be fine throughout.

Part P: This will be notifiable work. Clearly this is a new circuit, and it returns to the consumer unit, and it will involve work in a kitchen and bathroom.

 

[ericmark]

I live in a small two bedded house with a single lighting circuit that covers all 8 lights in the building, upstairs and down, and has no earthing. It looks very old - red and black PVC. A couple of questions arise:

1. Is it essential to have separate up and down circuits for lights? The reason I ask is because splitting the circuit is not possible without changing the consumer unit for one with additional breakers. Can I just stick with the one circuit, given the low number of lights (800W, if all 100W bulbs, but actually is now about 250W due to CFLs)?

This is to comply with 314.1 Every installation shall be divided into circuits, as necessary, to:
(i) avoid hazards and minimize inconvenience in the event of a fault
(ii) facilitate safe inspection, testing and maintenance (see also Section 537)
(iii) take account of danger that may arise from the failure of a single circuit such as a lighting circuit
(iv) reduce the possibility of unwanted tripping of RCDs due to excessive protective conductor currents produced
by equipment in normal operation
(v) mitigate the effects of electromagnetic interferences (EMI)
(vi) prevent the indirect energizing of a circuit intended to be isolated.
I have complied by simply fitting an Emergency light on landing which lights stairwell. There are no hard and fast rules.

Upstairs is pretty simple - there are four lights looped with connections in the ceiling roses. The end of the lighting circuit is in bedroom 2.

2. I imagine replacing all the circuit cables with 1.5 T+E running over the top of the loft insulation, and 1.00 to the switches would do it. Does this sound right?

Strictly speaking No! 433.2.1 Except where Regulation 433.2.2 or 433.3 applies, a device for protection against overload shall be installed at the point where a reduction occurs in the value of the current-carrying capacity of the conductors of the installation.

Although often it is done as you say and there is no real problem as even 1mm cable is rated 8 amp Reference Method 103# (in a stud wall with thermal insulation with cable not touching the inner wall surface)

Downstairs is more complicated. There are 4 lights, plus the feed to the upstairs part of the circuit. I haven't fully traced the wires yet (furniture) but I have found a junction box under the floorboards which definitely feeds the upstairs part of the circuit (1) and, judging by the number of wires leading from it, has the switch and power for the kitchen light coming into it (2,3) as well as power coming in (4), which may be via a loop into either the hall or sitting room light, or both. Then there is a fifth 1.0 twin...

This is where you are likely to come across problems in many old houses only twin and earth was used between the 2 Two way switches used for up and down stairs and if this is the case splitting up and down stairs supplies will cause a borrowed neutral scenario. If full rewire then not a problem of course.

3. Does Consumer unit to loop into hallway, then loop into pantry, then loop into sitting room, then junction box to kitchen, and finally upstairs sound like a reasonable plan? It's a longer cable run (the circuit goes to the sitting room light and back on itself to get back to the junction box), but it avoids having more than 4 wires going to the junction box...

Cable is allowed a 3% volt drop with 1mm cable and working on 6A MCB with 13A rating on cable corrected volt drop per meter 39.4 mV/A/m which will allow 29 meters if full load at end of cable with even distribution more like 34 meters of cable for volt drop be become a problem.

Earth loop impedance will depend on if you are using a RCD or not and for bathroom it needs RCD anyway and unless your using Ali-tube cable then the 50mm buried in a wall rules will likely require RCD anyway. If not total will be for B6 MCB 6 x 5 = 30 amp for magnet part of trip so 230/30 = 7⅔ ohms remove from that the Ze which will leave around 7 ohms which will allow more cable to be used than the volt drop will permit but you must calculate using value you have for Ze

In theory you can apply to council and pay Part P fee and DIY. In practice although will DIY people can drag in new cables OK when it comes to presenting paperwork it becomes a problem. The LABC will be responsible for safety and it seems very grey as to what they can ask you to do. Before the power is turned back on you may be required to present them with an installation certificate showing the calculated Zs for the circuit. The council is responsible for any testing by other than yourself but as Electricians we only hear second hand the problems people get with their councils over testing as even where we have to go through the council we have the test gear and qualifications to sign our own installation certificate to submit to council to get completion certificate. I would go in first and have a chat with building inspector by time you have paid him the £100 plus it may be better not to DIY. Remember they may make you wait until all tested before you can turn power back on. Some councils it seems are very helpful others do all they can to dissuade people from DIY.

As to getting out of Part P seems you can replace like for like but there would be little point in that. And of course you can break the law. What you need to consider is:-
1) If you sell the house you will be asked for the completion certificates which can’t really be got after the event.
2) Should you need to claim on insurance you may also be asked for completion certificates.
3) If anyone is injured in your house due to an electrical fault, this includes any other trades man who may do work for you in the future, you would be responsible and you will not be insured.
All excuses you use for not requiring it to be registered under Part P may make you feel OK. But unlikely to stand up in court should anything go wrong.
I see many people breaking the speed limit and all is OK until they get caught. Same with Part P.

 

[DeadJoe]

a device for protection against overload shall be installed at the point where a reduction occurs in the value of the current-carrying capacity of the conductors of the installation.

Isn't the most important part of this phrase 'current-carrying capacity'? That's how I was reading it. What I have assumed is that because of the depth of insulation in the (highly-insulated) loft that the lighting circuit must drill down through to reach the ceiling roses, the current-carrying capacity of the 1.5mm cable is reduced. Therefore, there is likely to be no actual reduction in current-carrying capacity, even though the cable size is different. In effect, the environment the loft cables are in has the effect of de-rating them, and the increased cable size covers this...

Earth loop impedance will depend on if you are using a RCD

At some point, someone has fitted a consumer unit with RCDs...

All excuses you use for not requiring it to be registered under Part P may make you feel OK. But unlikely to stand up in court should anything go wrong.

Good point. At the moment I am just exploring the possibilities.

 

[ericmark]

a device for protection against overload shall be installed at the point where a reduction occurs in the value of the current-carrying capacity of the conductors of the installation.

Isn't the most important part of this phrase 'current-carrying capacity'? That's how I was reading it. What I have assumed is that because of the depth of insulation in the (highly-insulated) loft that the lighting circuit must drill down through to reach the ceiling roses, the current-carrying capacity of the 1.5mm cable is reduced. Therefore, there is likely to be no actual reduction in current-carrying capacity, even though the cable size is different. In effect, the environment the loft cables are in has the effect of de-rating them, and the increased cable size covers this...

There has to be some common sense although the regulations say you should not change conductor sizes most people will and I can see no problem if all conductors are rated at 6A. But you asked question so I gave answer. Because twin and earth comes as 1.5mm normally and triple and earth in 1mm it is quite normal to mix. But had some pedantic inspector picked you up on it you would need to know the regulation.

Earth loop impedance will depend on if you are using a RCD

At some point, someone has fitted a consumer unit with RCDs...

All excuses you use for not requiring it to be registered under Part P may make you feel OK. But unlikely to stand up in court should anything go wrong.

Good point. At the moment I am just exploring the possibilities.

I would guess the lights have been put on RCD because the earth is missing the Electric Safety Council recommend this approach. As to Part P for electricians it has worked in that now the guys are following the rule book as losing their ability to self certify would be a big thing. However for the very large firms it does not seem to work they know the organisation will never withdraw their licence and worse case scenario they may have to sack any worker caught with wrong doing. The DIY part of the regulations is in complete disarray with councils charges being completely disproportionate to the work being carried out. With min charge being for a £1000 worth of work small jobs like change a thermostat for one which also contains a timer 10 min job being charged in Wales at £100 plus vat many DIY'ers are understandable ignoring the law. However where one needs to show improvements have been completed your hands are tied. One thing which does sometimes happen is an electrician will accept payment for planning and inspection and testing and will put his name to having done the work. He basic is employing you as his labourer however some have been stitched up by the DIYer not doing as he was told and have lost their Part P status as a result so finding one willing to do that now is very hard.
Also councils do not all have same charges or provide the same services some do as they should and do the whole inspection and testing and are very helpful others seem from reports on forums to put everything put in the way of the DIYer.
For electricians mixed blessing as although it can be cheaper to employ an electrician than DIY they have to follow the rule book so have to refuse jobs where the completed work will not be up to scratch.
For you with such a big job I would think the £100 plus vat to council is worth while although you may want to add any other electrical work at the same time.