Only one lighting circuit..

[an203888]

I only have one lighting circuit for my 4/5 bed house and am adding a fair few more lights to it. Is this acceptable and when should a second circuit be installed?

 

[JohnD]

Acceptable, used to be.

Good practice, no

One lighting circuit for each floor of your house is now recommended

In some cases, split it by Wing of your house

A separate circuit for outdoor lighting, that can be isolated when (not if) water gets into the electrics is a good idea.

 

[an203888]

Umm, so definitly create a new circuit for the outside lights and possibly another circuit for my extension which is likely to have about 35 lights in it

 

[bernardgreen]

so definitly create a new circuit for the outside lights

Yes and include a double pole isolator ( disconnecting both both Live and Neutral ) to ensure a damp or damaged lamp cannot trip the RCD

 

[an203888]

Yes and include a double pole isolator ( disconnecting both both Live and Neutral ) to ensure a damp or damaged lamp cannot trip the RCD

Where would the isolator go? Thanks

 

[bernardgreen]

Where would the isolator go?

If you are creating a new circuit from the consumer unit and adding a new MCB for the outside lights then I would put the isolator close to the consumer unit

 

[an203888]

If you are creating a new circuit from the consumer unit and adding a new MCB for the outside lights then I would put the isolator close to the consumer unit

Brilliant thanks. Makes perfect sense.

 

[JohnW2]

One lighting circuit for each floor of your house is now recommended

Sort-of - if you regard "take account of hazards that may arise from the failure of a single circuit such as a lighting circuit" as being a 'recommendation' to do as you say. As you are aware, there is quite a spectrum of individual interpretations of the regulation to which you refer.

I presume their thinking was that if (during the hours of darkness) the downstairs lighting fails whilst one is cooking dinner in the kitchen, one can abandon that activity and, instead go upstairs and 'read in bed' - or if the upstairs lighting fails whilst one is reading in bed (or taking a shower), one can abandon that activity and go downstairs and cook a midnight feast in the kitchen?

The greatest theoretical 'hazards' of a sudden loss of lighting (whether due to operation of a protective device or a power cut) are in the first few seconds (e.g. dropping pans of boiling oil), in whatever room(s) it occurs in.

Beyond that first few seconds, many rooms in many/most houses have a means of lighting (e.g. table/standard/bedside lamps) which is powered from a sockets circuit (hence still available if a lighting circuit alone fails), and even switching on a TV will often produce enough light to be able to 'see what one is doing' (hence 'avoiding hazards'). Indeed, in my bedroom even the digital time displays on bedside clocks/alarms produces a surprising amount of 'illumination' if the room is otherwise 'pitch dark'!

As I've said repeatedly, whilst mileage obviously varies, in my case by far the most common causes of our 'being plunged into darkness' are (usually very brief) power cuts (a problem which will persist no matter how many lighting circuits I have) - so that if 'they' are concerned about the immediate theoretical hazards associated with loss of a lighting circuit, they really should (at least for me - and I presume I'm not alone) require the installation of emergency lighting.

Kind Regards, John

 

[ericmark]

My old house had one circuit, so did mothers, there was a problem at one point with silly down lighters at 50 watt a pop that 6 amp was starting to be considered not enough, but my large living room today has 8 x 6 watt LED lamps, so load is very low.

I can see the point in two ring finals split side to side of the house so you can keep things running in an emergency with extension leads. But you can't really do that with lights so putting outside lights on their own circuit yes, but as long as 1380 watt is not exceeded and 9 mA of earth leakage not exceeded a single circuit is enough.

Yes I have emergency lights to light the stairs, but that is about it. Kitchen has under counter lights, and cooker hood lights independent and near every other room has a table or standard lamp, however although my house is all RCBO so many houses the most likely failure of lights is due to other items being put on the same RCD.

It does make some sense not to have lights and sockets in the same room on the same RCD, however for sockets the most sensible split is side to side, it reduces the loop impedance and removes the temptation to run extension leads on the stairs if you can't reset one circuit, so with two RCD's the only option with lights would be to use the same split.

However there are problems splitting lights. It was a common practice years ago to borrow the line from another switch when setting up two way switching, as well as interference with hearing aids this also means both lights must be supplied from the same over load device, so one has to be very careful when splitting not to cause what is called a borrowed neutral, it is the line that is borrowed, but called a borrowed neutral.

So to the question when should a second circuit be installed, I have found some lamps use more than the label states, mainly fluorescent, so I would say 1000 watt, the books said allow 50 watt per lamp, but today even 20 watt is likely going OTT. I would say around 10 watt is a reasonable average. As to a RCD being considered as a circuit, it seems 9 mA is considered as maximum permitted total for all circuits on the same RCD.

With a high integrity board it would seem reasonable to put lights on their own RCBO, but actually since most earth leakage faults are down to the ring final, it may be better to put ring final on RCBO's.

However if you look at work and expense fitting new RCBO's and notifying the work I would say these

plug in torches are a better option as they also work with general power cut, and far cheaper than fitting new circuits.

 

[JohnW2]

Yes I have emergency lights to light the stairs, but that is about it. Kitchen has under counter lights, and cooker hood lights independent and near every other room has a table or standard lamp ...

As I said, that's very common - it's certainly true of my house.

It does make some sense not to have lights and sockets in the same room on the same RCD,...

It does - otherwise the under counter lights, cooker hood lights, table/bstandard/bedside lights (and even TVs) are of no use if the lighting circuit fails.

I would say these .... plug in torches are a better option as they also work with general power cut, and far cheaper than fitting new circuits.

Exactly, that's the point I keep making - that any sort of emergency lighting, whether 'proper' or those cheap 'emergency torches' is the best way of removing potential hazards due to being plunged into darkness, since they will work in response to a power cut (far more common for me than RCD trips) as well as RCD/MCB trips - something that any number of multiple lighting circuits or RCBOs cannot achieve.

It is therefore my personal belief that, despite the way in which many choose to interpret it, the regulatory requirement to "take account of hazards that may arise from the failure of a single circuit such as a lighting circuit ..." is actually better satisfied by having some sort of emergency lighting (even if only one lighting circuit) than by having even umpteen lighting circuits, each on their own RCBO. After all "the hazards which may arise from the failure of a lighting circuit" are no less if the 'failure' is due to a power cut than if they are caused by operation of a protective device.

Furthermore, as I wrote recently, it is during the first few seconds after being plunged into darkness that the worst potential hazards arise - so, unless it just happens that a light powered from a sockets circuit is already switched on in the room at the time, even having lighting and sockets on different RCDs will not alleviate the worst potential hazard due to an RCD operating - but, again, emergency lighting (triggered from the lighting circuit) would.

Kind Regards, John

 

[ericmark]

I do remember arguing at work that an emergency circuit to supply emergency lights is daft. It had been done so it could be turned off to test the emergency lights, but the results were if a lighting circuit failed rather than a total power failure the emergency lights remained off, I also had a problem with discharge lighting, power failure would switch off lights and emergency lights came on, great, but when the power returned the main lights took some minutes to come on, but the emergency lights went off immediately.

However there is a difference with 20 odd people wandering around in darkness, to 2 people at home. One has to assess the risk, and it will change home to home, for example @JohnW2 has assessed the risk and decided there is a greater risk from a total power cut than from an RCD tripping, my last house was the reverse, RCD trips were regular, this house only RCB (RBCO) trips have been due to water ingress and I have never lost lights.

Again mothers house a RCD, MCB, or RCBO trip could be corrected from within the house, very rare anyway, but so easy to reset likely would not remember it tripping, my last house and this one involves going out of the house and into another part of the house to reset them, so a trip at night is a big thing, and the main risk is falling when going to reset the trips.

So I have 5 bedrooms although only 3 used as bedrooms, and three lighting circuits, one for each floor, however load on all three is rather low, the centre on does have 4 outside lights on it which is not ideal, but other than outside lights the three could be combined without any real problems.

And although using all RCBO the three circuits are independent, few homes are all RCBO, so with two RCD's it would be impossible to split into three independent circuits. I have a cheap Lidi emergency light at top of stairs, so with a power cut I can find way to torch and use it to find my way to room under main house where the trips are, also a simple torch kept at back door.

There is nothing wrong today with a 6 amp supply to all lights, the 50 watt down lighter is now 7 watt with LED, I have not got around to swapping all bulbs to LED yet, there are some seldom used rooms still with tungsten, but think 14 light units, at an average of 60 watt that is less than 4 amp, so no real reason for three circuits.

When I moved in a year ago I found there was an error in one switch where wrong neutral was used, only one wire in wrong hole, but potential dangerous for anyone working on the system, as to if this house originally had lights split I don't know, but seen it so many times when lights split where a wrong neutral has resulted.

I could hardly believe it when an electrician who should have known better suggested putting both lighting MCB's on the same RCD so the borrowed neutral would not trip the lights, combining them again so on same overload device yes, but he did not even seem to realise what he was doing was wrong. Some times people do worry me when they are clearly lacking education. But if so called electricians can get it wrong, clearly not a DIY job.

 

[aptsys]

Sort-of - if you regard "take account of hazards that may arise from the failure of a single circuit such as a lighting circuit" as being a 'recommendation' to do as you say. As you are aware, there is quite a spectrum of individual interpretations of the regulation to which you refer.

My interpretation of that reg is that if you can segregate circuits, then do. However many are quite many are quite militant over that reg whereas I see many single points of failure whereby all lighting could fail.

If the risk to occupants due to a loss of lighting is high, emergency lighting should be fitted rather than insisting the circuits should be split.

 

[aptsys]

When I moved in a year ago I found there was an error in one switch where wrong neutral was used, only one wire in wrong hole, but potential dangerous for anyone working on the system, as to if this house originally had lights split I don't know, but seen it so many times when lights split where a wrong neutral has resulted.

I could hardly believe it when an electrician who should have known better suggested putting both lighting MCB's on the same RCD so the borrowed neutral would not trip the lights, combining them again so on same overload device yes, but he did not even seem to realise what he was doing was wrong. Some times people do worry me when they are clearly lacking education. But if so called electricians can get it wrong, clearly not a DIY job.

Combining the two circuits is a valid solution to a shared neutral if separation is not feasible or are you referring to the fact they should have troubleshooted the wiring?

 

[ericmark]

Combining the two circuits is a valid solution to a shared neutral if separation is not feasible or are you referring to the fact they should have troubleshooted the wiring?

Combining two circuits no problem, i.e. both from same MCB, but putting both MCB's to be powered from same RCD is not, it may work, but not allowed. I have seen it more than once, where the cure to RCD tripping with a combination of two way switches has been cured by putting both MCB's power from same RCD. The other one is where down lights fitted and the load is too high, swapping the MCB from 6 amp to 10 or 16 amp when the ceiling rose is used as a junction box and is rated at 5 or 6 amp.

I know the latter likely will do no harm, but it is still not correct, and OK when it's a case of get it running until morning when I will return, but not a permanent cure.

If there is any junction box be it part of ceiling rose or switch back box which is rated 6 amp, then clearly can't fit a 10 amp MCB.

 

[AndyPRK]

So what is the issue of having 2 light MCB's on one RCD? They both connect to the same neutral bar.