Could someone (Adam?) please point me at the relevant slice of the
17th Ed, dealing with the number of circuits needed, both lighing and ring. I've got a couple of on-sites and Tricker's "Regs in Brief", but can't find it specifically in any of them.
I'm familiar with the 100m^2 floor area limit on rings, also the recommendation to separate out the kitchen. However I understand there's also an aspect for splitting circuits floor by floor, and I can't find the primary source of this. In particular, how strong is the requirement to split circuits across the upper two floors of a three storey house, when the load up there (bedrooms and bathroom) is fairly low anyway?
Also where does the prohibition on borrowing neutrals across stairway lighting come from, and what are the implications of this. Is there (AFAIR) also some requirement on feeding stairways from separate circuits, so as to maintain some lighting after breakers tripping?
Not that I'm aware of. A sensible design will try to:
Make circuits reasonably logical
Ensure the circuit layout is appropriate for the expected loads
(not exclusive)
My dormer bungalow has the following design:
Ground floor hall + right side bedrooms, 32A ring 1 (tight geographically)
Kitchen - 32A compact ring serving a high load worktop (2 machines, kettle, microwave, toaster etc
Rest of kitchen + 3rd bedroom behind it (both are on the left of the hall) - 32A ring 3. Most of the kitchen sockets on that ring are expected to be low load (laptop at dining table, floor lamps, that sort of thing.
Whilst one could argue it would be logical to have all bedrooms on on ring, it was more logical for cable run reasons to have bedroom 3 and the kitchen on one.
Lighting is done on a front/back split - ie 10A for back upstairs and downstairs;
10A for front upstairs and downstairs.
As all the wiring goes through under the upper level floorboards, this is logical (though unconventional). It also has the advantage that a failure in one circuit does not black out an entire floor.
Allow for the fact that if the heating fails, you might have an electric heater or two going up there. But as you say, generally low average load.
You don't do it, ever - although you do come across old bodges.
If you mix the neutrals between circuit A and B, then you turn off the MCB on A to work on it, you disconnect A's neutral at the CU only to find it is now at 240V via some light on circuit B that used A's neutral.
Bad - very bad...
No requirement (at least domestically) - but if you are worried, you can install a battery backed emergency light.
Kitchen is generally made a separate 32A ring. If the kitchen shared a ring with the house all the appliances may be at one end of the ring, thereby creating an imbalanced ring by design (one leg carrying 24A, other leg carrying 8A). You can use a 32A radial via 4mm FTE if wiring space is restricted, the length limit of
32A radials is avoided by use of an RCD. A radial wired in 4mm FTE has a single 1.5mm CPC, creating a higher EFLI than that obtainable by a ring wired in twin 2.5mm FTE with two 1.5mm CPCs, hence the length limitation where an RCD is not used.
Borrowed neutrals are not permitted. To do so breaches regs from decades back, but also creates a serious electrocution hazard: you test dead only to remove the wire and find it becomes live in your hand because it is still supplied from a circuit breaker you did not turn off.
Hall lighting. If redoing the hall lighting, use 3C+E, consider emergency lights (small LED units exist), perhaps put the hall on its own circuit although there is no requirement or current recommendation to do so. I know of one EE who has his hall lights on their own RCD protected circuit and supplied by a BS1362 cartridge fuse - his stairs would trouble a mountaineer and continue down past the ground floor to a limestone floor cellar :-)
Smokes. Smoke alarms are a pertinent matter when you have 3 stories, wire in 3C
+E and check any existing have not been wired in 2C+E with the earth used as the interconnect - absolutely non-compliant like borrowed neutrals.
If you are tearing the place apart, and this is a 3 storey house, leave in some extra 20mm or 25mm floor to ceiling conduit for any future expansion - telephone, network, satellite, power, X10, whatever. We seem to be creating more wires rather than reducing them
- copper association's the world over will be proud :-)
Fix borrowed neutral on hall lights. If you merely want to rectify a borrowed neutral, you can buy 6181Y in
1.0mm & 1.5mm online cheaply (sheathed singles), or 6241Y likewise (sheathed single with CPC) which can be used to solve the problem with a little work. For example if the hall borrows the live off the downstairs circuit and uses the upstairs for the neutral, you run a live from the upstairs light switch (permanent live) to the hall light switch which is re-run in 3C+E. The upstairs light switch is usually pretty close to the hall light switch, so it can be very easy and in zone (horizontal along wall from upstairs light switch to hall light switch on the landing). Alternatively you can sometimes rewire with occupancy sensors (like a PIR) thereby eliminating conventional light switches, no idea if there is a restriction on their use in a hall. Alternatively go french with a remote relay box and converting the existing switches to push-type for signalling. Alternatively using a wireless switch technology like MK Echo or something-similar-by-GET (MK is battery-less based on Piezo, others use batteries).
There are no rules about having upstairs/downstairs circuits. It is the traditional way of wiring the circuits but it is not a rule. It would make far more sense in many houses that have concrete floors and a CU in the kitchen to have the kitchen on it's own ring and the rest of the house on another.
It is worth noting that the 17th edn OSG gives a maximum cable length due to voltage drop with a 32A type B MCB of 106m for a ring (limited to 46m for a non RCD TN-S supply due to the earth loop impedance).
314-01-04 each final circiut shall be connected to a seperate way in a distribution board. The wiring of each final circuit shall be electrically seperate from that of every other final circuit.
So if the landing light takes its live from the downstairs lighting MCB but has the neutral connected to the upstairs lighting neutral then turning the upstairs lighting MCB off to change a bedroom light fitting will not guarantee that the bedroom light is not live.
Again there is no requirment to have the landing light on its own circuit. Most houses still have an upstairs downstairs lighting setup and most people manage quite well with that set up.
Yes, but where's the section in the 17th Ed that say this? For it probably says a bit more than "Borrowing a neutral, it's bad like stealing" and I'd like to check the details too.
Circuit breaker? Lighting from more than one circuit? Luxuries!
8-) All of my lighting is currently supplied through one twist of fusewire. Except for an outside light, which (by proximity) appears to be piggy-backed on an extractor fan, which is supplied by something in the kitchen. Something with suspiciously fat cable. So yes, that's an outside light, wired in ancient damp string, with no RCD and a 32A cooker fuse...
That's rather what I _don't_ want, as I'd prefer to avoid single point failures on the stairs. I don't need _much_ light on the stairs - switching on any of the three is adequate light to navigate them in extremis. Yet if I start splitting the lighting by floors, I'd best check the full rules against borrowing beforehand.
Yes, I should probably think about that too. We're just a million separate battery ones at present (currently having the Autumn chorus of cold, dead PP3s)
been wired in 2C+E
2C+E ? You mean something that isn't brittle black rubber? 8-)
If I could think of somewhere to run it, I would. There just isn't any obvious straight path on which to do it. I might yet build a boxed conduit from top to bottom along the only solid wall. The other walls are lath and plaster and don't line up between floors.
It's not. It's on a quite separate wooden pattress. I also have no idea where most of the 1st floor cables run, except for those that run alongside a heating pipe (toasty!) The only vaguely new cable in the building, and probably the worst routed.
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 sec 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 circuit conductor currents produced by equipment in normal operation. (v) mitigate the effects of EMI. (vi) prevent the indirect energising of a circuit intended to be installed.
314.2
Separate circuits shall be provided for parts of the installation which need to be separately controlled, in such a way that those circuits are not affected by the failure of other circuits, and due account shall be taken of the consequences of the failure of any single protective device.
314.3
The number of final circuits required, and the number of points supplied by any final circuit shall be such as to facilitate compliance with chapter 43 for overcurrent protection, sec 537 for isolation and switching and chapter 52 as regards current-carrying capabilities of conductors.
314.4
Where an installation comprises more than one final circuit, each final circuits shall be connected to a separate way in a distribution board. The wiring of each final circuit shall be electrically separate from that of every other final circuit, so as to prevent indirect energising of a final circuit intended to be isolated.
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ECA - ADEQUATE PROVISION OF ELECTRICAL SOCKET OUTLETS IN THE HOME (PDF)
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17th edition consumer units guide
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This is a guidance limit.
17th Appendix 15 1 (iv).
Ring final circuits Reg. 433.1.5
The load current in any part of the circuit should be unlikely to exceed for long periods the current carrying capacity of the cable (reg 433.1.5 refers). This can generally be achieved by: (i) locating socket outlets to provide reasonable sharing of the load around the ring. (ii) not supplying immersion heaters, comprehensive electric space heating or loads of a similar profile from the ring circuit. (iii) connecting cookers, ovens and hobs ith a rated power exceeding 2kW on their own dedicated radial circuit. (iv) taking account of the total floor area being served (As a rule of thumb, a limit of 100m2 has been adopted).
The relevant comments for radial circuits are:
20A overcurrent protective device - Rule of thumb for floor area served is 50m2.
30A or 32A overcurrent protective device - Rule of thumb for floor area served is 75m2.
The above information is also summarised in Appendix 8 of the on-site guide, where the areas served are prescribed. I guess the on-site guide needs to be amended to make it clear that the areas are rules of thumb not absolute limits.
also the
All good practice and passing compliance with sec 314.
In particular, how strong is
No requirement at all as long as the cable isn't too long and you are confident about complying with sec 314 and sec 433.1.5.
Sec 314 doesn't allow it. Section 521.8 specifically prohibits it.
I would guess it is implied from some rule that says different circuits shall be electrically separate, except for supplimental bonding, or something like that?
I'm mostly doing that for two other reasons: the CU is in the middle of the house, adjacent to the kitchen. It's just simpler routing. Also in a couple of years we might demolish the kitchen (that's roof and half the walls gone, Grand Designs scale demolition!) and easy separability then will obviously be useful.
Not a problem here. It's not that big a house. TT (overhead) incidentally.
Ah! One of those great unstated things, implied by a simple statement that looks like the bleeding obvious and no more.
So, 3 ring circus (top 2, bottom, kitchen) it is then.
It actually does not take long to use up a 100m drum of 2.5 T&E even in a small house when there are lots of sockets downstairs and they have concrete floors and high ceilings.
521.8.2 The line and neutral conductors of each final circuit shall be electrically separate from that of every other final circuit, so as to prevent the indirect energising of a final circuit intended to be energized.
The line and neutral conductors of each final circuit shall be electrically separate from that of every other final circuit, so as to prevent the indirect energising of a final circuit intended to be
I think you are trying to light each floor of the stairs by each floor level's lighting circuit - so if another floor trips off you still get some light on the stairs?
That can be done by a) having push-switches and a relay/timer system like the French use - so any switch on any floor causes all levels of stair lights to turn on/off - BUT each floor is on a separate lighting circuit for "redundancy". ... b) having stair light switches on each level of stairs just connected to that floor level's lighting circuit - that means you switch on at the bottom of each stairs and off at the top, the two switches being 2- way switched, linked via 3C+E (3-core and earth). On the next level of stairs you have another switch. That may work with landings at each stairs sort of like a hotel, or it aesthetically may look a bit odd with switches next to one another re "left switch for stairs behind you, right switch to stairs above you" although I dunno it has its attractions if a relative is being a PITA :-)
I think the simplest solution is Hall lights on dedicated RCBO and Em- Light in case that circuit fails.
The EE created his own Em-Lights via LED GU10 powered off the burglar alarm 12V 7Ah battery, triggered by NO relay off all the lighting circuits & smoke alarm circuit. Relatively cheap and more integrated than conventional Em-Lights.
Someone mentioned black mortar, where they used coal dust/ash to colour mortar and replace sand. That mortar, particularly when wet due to leaks, can cause TRS cable crossing it to degrade sufficiently to short out badly (close to the meter it welded the MCB contacts and took out the BS1362 60A main fuse, along with showering plaster everywhere). The cable sheath was cracked most noticeably at the mortar crossings, particularly where there was water penetration (water crossing to inner leaf by brick return linked wall vent above and a recent guttering leak).
So whilst TRS may appear ok, it can still go bang in a wall for little reason.
Of course they could closer if you do a rewire. It is unusual not to have this type of setup.
One very easy way to see the stairs if one MCB trips is to two way the hallway lights on all floors (each floor has it's own MCB). So on ground floor you can switch the hall and 1st floor landing light, on the 1st floor you can switch all 3 floors hallway/landing lights and on the 2nd floor there is a switch to do the 1st and 2nd floor landing light.
But with 3 lighting circuits, not due to the loading but because you would not want two floors of lights to go out when a bulb pops.(You will find that out when you swap the fusebox for a CU)
Coming late to this party, so I won't bother covering all the stuff done so far...
Frequently 1st and second floor power circuits are combined - its quite common for loft conversions to be powered by extensions to existing circuits.
Aside from the obvious risks of cross energisation of a theoretically isolated circuit, there is also the point that RCD protected circuits tend to get upset by it!
Its traditional to have more than one lighting circuit certainly. The older practice of feeding hall and landing from the same circuit is deprecated (and that in itself was a simplifying two way switching without borrowed neutrals). If you do bi-directional two way switching then you ease the problem greatly since chances are you will be able to turn on at least one light from either end.
(I stuck a non maintained emergency light over ours!)
At present there's two-way switching on the upstairs floors, with a second switch on the floor below (Ground floor hallway is only on the ground).
We'd also like to have "period" switches, which is turning out to mean crappy anodised-gold aluminium toggles from TLC. I think they look awful, not much like toggles and not at all like brass, but it's what's available, what puts 3 switches onto a single faceplate, and what doesn't cost =A317 a toggle, as the decent real brass ones do.
OTOH, they can only support 2-way but not 3-way switching, as they don't do a crossover.
Another idea is to use ancient tumbler switches, but just run them at low voltage with a control box elsewhere.
If I powered each light from the _lower_ floor's supply, not its own floor, I'd have access to stairway lights on two different circuits from both the upstairs floors (top floor light is enough to see by). Only the ground floor then loses the ability to turn the lights on after a trip (and you can go fix it first).
I suppose you could create your own xover using a normal switch and a DPDT relay.
Touch dimmers might also do it - you can hang multiple slaves off each master - but you would need a master on each floor - which probably prevents you used the three gang ones.
I don't want to justify or excuse mixing neutrals, I think it's a daft thing to do. But nevertheless I'd like to ask: Why is it considered good practice to disconnect *both* live and neutral?
It seems to me that if one were only to disconnect live, then this particular problem would not arise, since all the neutrals would in effect be permanently bonded together, and never live, nor ever much different from earth.
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