Circuit design for new extension

[Mechie]

Hi all

I've got a training assignment to do which is to design a circuit for a job I will be doing with my boss. He wants to see what I come up with having viewed the job and spoken to the client.

Basically the job is supplying lighting and sockets to a new extension comprising of three double socket outlet, two wall mounted up lighters controlled by one side of a two gang switch and one downlight controlled by the other side.

As far as I can see there is no easy way to extend any current lighting or ring final circuits without making a lot of holes and a lot of work which the client doesn't want, but there are two spare ways on the consumer unit which is right next to the new extension. So my suggestion would simply be run two new circuits from the consumer unit.

Only problem is that the client thinks he knows a bit about electrics "maybe he does?" and has started going on about only using one way from the consumer unit, he wants a radial supplying the sockets and a fused spur feeding the 3 lights.

seeing as the max current demand for the lights is about 1.3amps and I can't find anything in the regs which says I couldn't run the lights of a 5amp connection unit spurred off the socket circuit or spurred off an exsisting lighting circuit at the consumer unit. Am I missing something in the regs? And should I design my circuit as the client wants, or is there any reason I should suggest that the two circuits be run from their own circuit breakers at the consumer unit, eg, future proofing if he wants to extend the circuits, or a deveation from the regs if I've missed one

I noticed that the RCD takes up 3 ways in the CU, so I could suggest putting in a newer smaller RCD that would leave room for another way off the CU for future extensions.

Just wanted to hear your thoughts before I hand my design over to my boss.

 

[Badged01]

I take the view that the customer is king ... he is paying your bills and more importantly he can recommend you for further work. If what he wants doing meets the regs and in your opinion is safe to implement then do it. A satisfied and happy customer is always good for business!!.

I actually see no problem with a radial circuit for 3 sockets with a 3A fused spur off this feeding the 2 lights.

 

[RyanCheetham]

I did something similar 2 weeks ago. No easy access to CU from the extension so i broke into an existing socket on the backside of the wall and extended the RFC for my 3 sockets and i used an FCU to power my lights and 3 plated all at the switch. Obviously i was lucky enough to have a wiggle room on the circuit to add the extra sockets without overloading. So yeah there is no problem with what you propose

 

[stuartcourt]

If you can get to consumer can you not come off an existing lighting breaker

 

[Mechie]

If you can get to consumer can you not come off an existing lighting breaker

As it's feeding multiple lights would this not still need a fused connection unit, if so then it makes sense just to run the one piece of 2.5 twin and earth from the consumer unit to the extension, then FCU off that for the lights, would save on cable.

 

[Spoon]

As it's feeding multiple lights would this not still need a fused connection unit, if so then it makes sense just to run the one piece of 2.5 twin and earth from the consumer unit to the extension, then FCU off that for the lights, would save on cable.

Just my opinion, but seeing as the CU is "right next to the new extension" as you mentioned in post 1, then doing as stuartcoart suggested would be better, as long as the circuit can take the extra load for the lights.

 

[Mechie]

Just my opinion, but seeing as the CU is "right next to the new extension" as you mentioned in post 1, then doing as stuartcoart suggested would be better, as long as the circuit can take the extra load for the lights.

Yeah i agree, I just want to be sure so i can explain exactly why i've designed the circuit the way i have to the boss and also to explain to the client if it's different from the way he wants it. End of the day the boss and the client will make the finale call, I just want to investigate all the options and show that I've actually put some serious thought into it. I know it's not the most complicated circuit or installation but the boss is letting me take the lead on this job so want to show I'm taking it seriously and not just taking the easy route.

 

[Octopus]

Yeah i agree, I just want to be sure so i can explain exactly why i've designed the circuit the way i have to the boss and also to explain to the client if it's different from the way he wants it. End of the day the boss and the client will make the finale call, I just want to investigate all the options and show that I've actually put some serious thought into it. I know it's not the most complicated circuit or installation but the boss is letting me take the lead on this job so want to show I'm taking it seriously and not just taking the easy route.

Given that your outline of the job suggests a single up front RCD, you should comment on the increased risk of nuisance tripping.

 

[odawire]

Hi all


I noticed that the RCD takes up 3 ways in the CU, so I could suggest putting in a newer smaller RCD that would leave room for another way off the CU for future extensions.

What do you mean? are you saying its three pole?

 

[stuartcourt]

No he is saying it sounds like one RCD protecting all circuits so if it trips then you lose power to everything. Back to the new circuits I would have thought your boss would rather lights on lighting circuit, only really put lights off spur if lighting is inaccessible.

 

[stuartcourt]

What do you mean? are you saying its three pole?

sorry got confused some older RCD took up 3 ways (spaces) on consumer unit rather than 2

 

[Mechie]

sorry got confused some older RCD took up 3 ways (spaces) on consumer unit rather than 2

Yeah you got it, sorry probably my fault for not using the right language to explain myself.

So I think I'm going ahead with suggesting running the lights of the existing light circuit in the CU, Looking through BS7671 I can't see anything that say's I should treat a domestic light circuit any differently from a standard socket radial. So as I can't really extend the current light circuit without disconnecting the current light circuit, running my new piece of 1.5 into the extension to the lights, then back to the CU to connect back the existing circuit, I guess this will still be consider a spur of the existing lights connected at the CU. as it's powering more than one piece of fixed equipment I will need to install a 3amp fused connection unit?

If so does it matter where this is located, is does it need to be close to the lights as a fused unit for a cooker would be, or can I install it at the start of the spur next to the consumer unit.


If i'm missing something really obvious in the regs would someone mind pointing me to the right section

 

[Spoon]

I think you are getting a bit confused Mechie, or I am....
If you are going to wire the light in the extension into an existing lighting breaker then you do not need any additional fusing down to 3A. Just wire it up as you would a standard lighting circuit. Again, make sure the existing breaker can take the extra load for the lights.

 

[Mechie]

I think you are getting a bit confused Mechie, or I am....
If you are going to wire the light in the extension into an existing lighting breaker then you do not need any additional fusing down to 3A. Just wire it up as you would a standard lighting circuit. Again, make sure the existing breaker can take the extra load for the lights.

No sorry, I thinks it's me getting confused as I've never wired a lighting circuit like this. So I have a 6amp breaker currently supplying the exsiting lights. What I want to do is also run the 3 new lights off this breaker. Looking in the On Site Guide, The Electricians Guide and BS7671 I can not see anything covering this exact situation, the closest I can see if diagrames and info on wiring a radial for sockets.

Appendix 15 in BS7671 states "an unfused spur run in 2.5mm2 cable should feed one single or one twin socket-outlet only. An unfused spur may be connected to the origin of the circuit in the distribution board."

For a fused spur it says the number of sockets supplied is dependent on the load, so what I'm asking is whether I treat the lighting circuit in the same way, eg as there is more than one light should I fit a fused connection unit or can i connect straight into the breaker without one. I've been looking through all the books but can't see anything that answers my question.

 

[Spoon]

The breakers in the CU are to protect the cables in the circuit. What you intend to do is wire the lights in the extension in 1.5mm, as normal. Then wire this circuit back to a 6A lighting breaker... Making sure the extra load is suitable.
What is the existing current consumption when all the light are on?

 

[Mechie]

The breakers in the CU are to protect the cables in the circuit. What you intend to do is wire the lights in the extension in 1.5mm, as normal. Then wire this circuit back to a 6A lighting breaker... Making sure the extra load is suitable.
What is the existing current consumption when all the light are on?

Will total 5,7amp including the 3 new lights so the breaker can handle it

 

[Octopus]

Now you've got some pointers, is it time to run it past your boss?

 

[skamuk]

In need of a little advice.

My uncle wants some decking lights and a single socket fitted in the shed at the end of the garden.

The CU in the house is old-school, and there are no RCD's present. I wouldn't know where (if) I could obtain one from this era.. so..

I obviously need to RCD protect everything in the garden. Ideally I want to spur off a ring socket in conservatory - drill through the back of the socket to the outside wall, and fit an RCD outside, as I don't want to damage the decorating inside, otherwise I would just chase one in next to the socket inside.

Problem with this is the price of weatherproof RCD's is extortion!

Can I put the RCD in the shed before the socket and lights, but after the 20m SWA run, or does that defeat the object? The cable is 2.5 SWA and is going to be clipped to fence.

Can't seem to find anything on this in the regs.

 

[Octopus]

In need of a little advice.

My uncle wants some decking lights and a single socket fitted in the shed at the end of the garden.

The CU in the house is old-school, and there are no RCD's present. I wouldn't know where (if) I could obtain one from this era.. so..

I obviously need to RCD protect everything in the garden. Ideally I want to spur off a ring socket in conservatory - drill through the back of the socket to the outside wall, and fit an RCD outside, as I don't want to damage the decorating inside, otherwise I would just chase one in next to the socket inside.

Problem with this is the price of weatherproof RCD's is extortion!

Can I put the RCD in the shed before the socket and lights, but after the 20m SWA run, or does that defeat the object? The cable is 2.5 SWA and is going to be clipped to fence.

Can't seem to find anything on this in the regs.

Are you sure this is a good idea?

 

[skamuk]

Just thought about how, when and why an RCD operates and realized what a stupid question I've just asked! :shame:

Better question... Anyone know of a (cheaper than £45) source of external RCD spurs?

 

[Octopus]

Just thought about how, when and why an RCD operates and realized what a stupid question I've just asked! :shame:

Better question... Anyone know of a (cheaper than £45) source of external RCD spurs?

If he's your Uncle isn't he going to be happy to pay a competent relative to install a quality solution?

 

[telectrix]

much easier to run SWA without RCD, then fit RCD and whatever over current devices in a garage board in the shed. alternatively, cut a box in adjacent to the socket carefully and fit RCD FCU there.

 

[skamuk]

much easier to run SWA without RCD, then fit RCD and whatever over current devices in a garage board in the shed. alternatively, cut a box in adjacent to the socket carefully and fit RCD FCU there.

But say for instance he damaged the SWA and the neutral comes in contact with cpc, if the rcd is after the SWA run surely it won't trip?

 

[telectrix]

that is true, but SWA does not require RCD protection in itself. the only protection required is for overcurrent and fault protection.

 

[skamuk]

Sorted. running swa to rcd spur (in shed), feeding unswitched FCU to feed lights, using 2 cores of the 4-core swa to run switch live for lights back at the house, same rcd spur also feeding single socket in shed.

Got it sussed i think. Cheers!

 

[skamuk]

Problem. Ran SWA from socket on ring in house, to rcd spur in shed, rcd spur feeding single socket and some low voltage decking lights via switched spur.. RCD spur trips when electricity is restored. My wiring is fine and everything works without the rcd present.. Could it be a problem in the house causing it to trip?

 

[Octopus]

Problem. Ran SWA from socket on ring in house, to rcd spur in shed, rcd spur feeding single socket and some low voltage decking lights via switched spur.. RCD spur trips when electricity is restored. My wiring is fine and everything works without the rcd present.. Could it be a problem in the house causing it to trip?

ha ha ha, come on then list the tests you have done.

 

[skamuk]

continuity between l-n l-cpc n-cpc. IR. No problems...

- - - Updated - - -

Tests carried out on my wiring only

 

[skamuk]

The only thing I can think of is the wiring in the house has seen better days, if there was a fault in there somewhere would it trip, if there was a residual current in the cpc? I thought RCD would only detect problems on the outgoing side and not the supply intake?

 

[bigbaddave]

As in tested ok.. What you mean what exactly are you test results?

 

[bigbaddave]

Is this for real bud?? Are you registered with a dreaded scam and what electrical qualifications do you have if you dont mind me asking

 

[bigbaddave]

continuity between l-n l-cpc n-cpc. IR. No problems...

- - - Updated - - -

Tests carried out on my wiring only

Wait a minute.. You have continuity between l&CPC and N-CPC.... A rcd picks up on what type of fault???

 

[Octopus]

For everyone else: read post # 35

http://www.electriciansforums.net/e...gulations/74813-please-help-3.html#post746812

 

[rattlehead85]

The phrase 'a little knowledge is dangerous' springs to mind. Alarm bells are ringing if you don't understand the working principles of a residual current device!!

 

[skamuk]

I understand how a RCD works, it monitors the voltage between L-N and if there is an imbalance between the two. The only way there could be an imbalance between the two is if one of them are leaking to CPC am I correct? and an rcd also has a cable that monitors the cpc so maybe this is what is causing it to trip... I don't know for sure this is why i'm here.

I didn't mean I have continuity between L-N L-CPC N-CPC, I tested for it, and got high readings all round. Murdoch asked what tests I carried out not what results did I get.

I'm not a registered electrician, but am at college studying c&g 2365 l2 and have near enough completed this year. Whole reason I'm on here is to seek guidance and learn from people who do have knowledge and experience... otherwise what is the point in the forum? So everyone can boast about how qualified and experienced they are, and have a go at the ones who aren't??

Every time I ask a question on here I get mixed messages, some wanting to help, others just want to harass you about your qualifications. I do appreciate the help. If it wasn't half term this week I would ask at college.

 

[dan86]

I do appreciate the help. If it wasn't half term this week I would ask at college.

you appreciate the help, but given the choice, you'd rather ask elsewhere?!

 

[Brightspark2]

I understand how a RCD works, it monitors the voltage between L-N and if there is an imbalance between the two. The only way there could be an imbalance between the two is if one of them are leaking to CPC am I correct? and an rcd also has a cable that monitors the cpc so maybe this is what is causing it to trip... I don't know for sure this is why i'm here.

No an RCD monitors current not voltage and to answer your earlier a question the RCD spur will not pick up a fault within the house. We dont install an RCD to protect against a neutral to cpc fault within a cable, we install an RCD to give protection for people using the circuit. Hence the SWA alone not needing RCD protection.

Seems like it's wired wrong to me....

 

[Octopus]

Do you own a MFT?

 

[skamuk]

Sorry yes it measures current and a neutral to cpc fault is one that it detects as well as a line to cpc fault. If there are 3amps being drawn by a load from the line conductor then the neutral conductor should also be carrying 3amps, if it is not the device will trip.

Yes I own a Metrel 61557 MFT.

 

[Octopus]

Sorry yes it measures current and a neutral to cpc fault is one that it detects as well as a line to cpc fault. If there are 3amps being drawn by a load from the line conductor then the neutral conductor should also be carrying 3amps, if it is not the device will trip.

Yes I own a Metrel 61557 MFT.

In which case time to dust it off and use it again.