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MG Midget and Sprite General - Perplexing House Electrics (NMC)

I hope this is simple, and you'll be able to help. The electrician who wired our new extension left me a twin + earth (I thought) sticking out of the pebbledash, ready for an external light to allow us to see what we're drinking as we shiver on the terrace on spring and autumn evenings.

Well I've bought one, and fixed the bracket nicely, but when I unscrewed the terminal box he'd left, there were 4 wires!! And with the switch off, one of the wires bit me!!

I put my tester across the terminals with the switch off, and got 240v between white and brown; with the switch on, 240v between white and black.

Two questions:-

1. What's going on?
2. How do I take the 4 wires into the 3 terminals on my new halogen fitting?
Nick

Ouch. Another reason why I'm dead dead careful with mains electrics and always use my electricians screwdriver to test +'vs before doing owt.

Not much help I know :-)
Tarquin

Sounds like your sparky may have set it up to give you 2 options. Option one being a permanent live which would work with a PIR (ie. a movement sensor). Option two being manually controlled via the switch - in which case you would need to joint out the permanet live in a joint box or isolate it at the feed. You will need to work out which is permanent live and which is switch live.

This is only a guess though. I would suggest speaking to the sparky to confirm how he has run his cables.

David
David Wigley (MK2 Sprite)

Electricity: You can't see it but it hurts like h*ll
Alex G Matla

Nick,

From your description, I think your electrician has set it up so that you can wire in a second switch outside to give you two-way switching. i.e. so you can switch the outside lights on and off from either indoors or from outdoors.

I would ring him to check.

Guy
Guy

The usual way to wire a light is to have a live and neutral incoming, a live and neutral outgoing and 2 wires to the switch. As this is an extra light, I doubt you would have an outgoing pair, so that leaves you four wires - excluding earths, of course.

You don't say what colours the wires are.
Dave O'Neill 2

Dave,
I think Nick lists the colours as brown, white and black (and presumably #4 is a yellow/ green earth)
Guy

Yes, Guy. I had overlooked that, somehow ;o)
Dave O'Neill 2

Perhaps the electrician has given you the option for a cieling fan with a built in light fixture...so the fan can have its own switch and the fans light fixture can have its dedicated switch...thus the 2 are independant of each other. You can run the fan without the light and vice versa
Prop

Oh ....and yes...if your not sure, why risk it now... Id drop a dime and call the electrician, for a fast chat...he wont be offended, and id think he would offer help just as a professional courtisy, not to mention a good measure of customer service after the sale.
Prop

Prop, the cable is outside - for an external light!
David Wigley (MK2 Sprite)

...you wrote "terrace" so prop was probably thinking covered porch (many covered porches here include ceiling fans). I wasn't sure what pebbledash was until I looked it up. It is a type of finish used with stucco'd walls...correct?
Trevor Jessie

Spot on, Trevor. Actually in this part of the country they call it roughcast, and it's intended to be painted (which is a PIG of a job).

Thanks all. I guess David probably has it right, because the other two external lamps, which the sparks actually fitted, are both PIR types - permanent supply - of course - doh.

Calling him to ask what's what is clearly the sensible answer - but you know how it is when you've assembled all the tools, got the ladders out, drilled the wall and fitted the bracket, and it's Saturday, with the next day being Sunday . . . . . . . . . . . . . . . .

I might just see if I can tell for sure which is the permanent live, and put it out of the way.
Nick

>>I might just see if I can tell for sure which is the permanent live, and put it out of the way.<< no don't do that - call the electrician permanent live means just that a live wire

I think electrical faults are still the main cause of house fires - high level of personal accidents are also from DIY

give the guy a ring and if you're not sure get him to do it
N Atkins

Job done.

Here's the logic problem (ignore my earlier test results, which were incomplete):-

With switch off:-
240v across white and brown

With switch on:-
240v across white and brown
240v across white and black

Identify white, brown and black, as (i) permanent live, (ii) switch live, (iii) neutral.
Nick

AS suggested, get the spark back, you could also have a look at the wiring in the switch, which should give you a clue.
Cheers John
HALL JOHN

Not wanting to criticize the electrician in question but we are now forced, I understand!! to wire instalations to the new colour scheme!!

In house instalations we have 3 colours blue brown and green/yellow
I bet however I am wrong!

Torq the screwdriver you refer too is not an electricians screwdriver? it is a fools screwdriver and any electrician using one should be kept well away from arms length. An approve voltage tester should be the tool of choice for testing for dead., the tool you have described is not such a beast and protects the user only by a resistor. Is that an acceptable risk? probably LOL.
Robert (Bob) Midget Turbo

Come on chaps! I isolated the permanent live in a nice little terminal block far from the action, and the light fitting is working.

If I (electrically challenged like you wouldn't believe) can work it out, so can you.

The only thing that worries me is why the MCB didn't pop when I got my belt from the live terminal. I thought the Residual Current Device was suppose to detect imbalance in the poles, e.g. earthing through my (admittedly sub-standard) body.
Nick

With switch off:-
240v across white and brown

With switch on:-
240v across white and brown
240v across white and black

Well it's not a two way switch then? Otherwise they would alternate depending on switch position. There goes my theory
Andrew Dunn

RCD only detect live to neutral. If the neutral is connected to earth as it is in most areas of oz the depending on your internal reistance it sholud see the inbalance. But IMHO I think your resistance to earth would just be seen as load on the circuit hence nothing tripped.
Col
c pearce

Hi Nick

I think the reason the RCD did not trip is because the lighting circuit is not protected by the RCD. Generally nowadays we have "split boards" that select which circuits are protected by the RCD and which are not. The vast majority in the UK have lighting circuitsNOT protected by RCDs.
As you say if it was protected then it should have tripped.
Bob Turbo Midget England

Even if Nick's lighting circuit was protected by an RCD the imbalance required to trip it would be 30mA (higher value breakers can also be used). 30mA is chosen because this is the value beyond which if the current passes through your heart, i.e. a shock that goes from one arm to the other, you are likely to go into ventricular fibrillation (a heart attack). If the jolt Nick got was below this level, it would’ve hurt but wouldn’t have tripped the RCD. As a point of interest when I did my training we were advised when working with high voltages to keep your left hand in your pocket, thereby preventing an arm to arm shock and limiting the current flowing through your heart.

Bob
R.A Davis

I can remember my grandad testing light fittings when ever a bulb blew. He just stuck his finger in the socket and pronounced "that's live!" He could also wiggle his ears. I don't know if the two were related. He's dead now!
Matt1275Bucks

Hi Bob

I think if anyone has an RCD that did not trip when the user got a "belt" then the very first action should be to immediately find out why and if necessary fit a new RCD. 30 ma is nothing and even touching the neutral bar to earth should be enough to trip the RCD. (touching the neutral bar to earth will not be felt at all) Bob have you had a belt that did not trip the RCD?

We as electrical engineers should be careful about the way we give out advice. When discussing electricity I tend to err on the dangerous side to ensure those with lesser understanding remain justly frightened of the consequencies. Having investigated the death of a child because of Xmas fairy lights many years ago (when they were 240V) and who can forget Ken Barlows first wife!? then I try to make people ultra cautious.
Bob Turbo Midget England

My house has a strange system of wiring installed (probably around 1961)

The lighting circuit is made up of individual red or black wires and the live feed is distributed around the light switches rather than the ceiling roses.

I can't think that it could have been standard practice for very long and I've not seen it used elsewhere.

Dave
D MATTHEWS

Bob

To receive a shock that exceeds 30mA the resistance from the point of contact to ground would need to be less than 8K ohms. With reasonably dry skin and probably earthing via their shoes to ground I would suggest their total resistance wouldn't be less than the 8K ohms required to trip the RCD, this wouldn't however stop them getting a nasty jolt. If you make contact with both live and neutral it doesn't matter how much current is flowing the RCD won't trip.

I trained as an Electronics Engineer working with voltages considerably in excess of 240V. The highest voltage I've worked with was 4KV and the highest belt was from 600V DC, that threw me across the room. These days anything above 12V makes me nervous and I don't touch anything mains voltage without testing it first with a voltstick and I test that's working first.

Anyone doing any work with mains voltages needs to have a complete understanding of what they're doing and treat it with extreme respect. My respect for mains voltages stared at an early age, the first shock I can remember was at the age of about 5 or 6 when I poked some aluminium foil into an electric fire, at about 10 I also got a very nasty shock from some fairy lights and a couple of years later I learned you don't try to remove a live socket with a metal pen knife. Other things I've learnt is don't cut live cables, it makes a big bang and ruins your cutters, and be very careful about touching cables while at the top of a ladder.

Deirdre Barlow was fiction Mary Wherry, Jenny Tonge’s daughter, was real.

Bob
R.A Davis

Having had a small connection with Electricity and Gas (Boards, for those older enough to known) I've seen some amazing bits of DIY and it's a testiment to our British Standards that more properties haven't been burnt or blown up and more peole injuried or killed

Carbon monoxide poisioning it's a pleasant thing to experience or killing yourself or others by so forget the hose on the exhaust and check your appliancies and flues/chimneys regularly

Carbon monoxide stays in peoples' systems for a good while possibly causing complications even when it doesn't kill them

I'm not sure about electric shocks but burning to death or very badly is very nasty for those invovled and not just the direct victim

Do the wiring job compently or get the electrician back or wire up a latent problem that could potentially be a silent killer of your family? - there was that stressing the dangerous side enough

PS I'm not the person of the same name as mine that was a fireman and deals with issues as I've just put
N Atkins

<<My house has a strange system of wiring installed (probably around 1961)>>

I was talking to an electrician last week who was telling me that the latest wiring for lighting circuits is just as you described, with the lives going from switch to switch, although you now have two T&Es going down the trunking, so if you are rewiring, it makes it a really difficult job.
Dave O'Neill 2

Dave,
That sounds like a radial system for your lighting. It was commonplace up until the mid 1970s. The real problem was the horrible junction boxes often used with far too many cables crammed into poorly connected blocks.

Nigel, are you OK? I have just read your message several times over, and although the gist of it sort of makes some sense, the actual sentences are, well, sort of muddled! Been testing the local beer perhaps on a hot day?

Guy
Guy

Guy it might be the lack of beer !

For Board I don't mean board, I mean Board, as in ** Gas Board or **Electricity Board as in organisations not the boards the meters and consumer units went on

Carbon monoxide is what you get when gas isn't burnt properly from appliancies fitted incorrectly - or not serviced, or correctly - or blocked or cover flues/chimeys, you also get it from car exhausts

there, now that's clear perhaps I don't need a beer

anyway they've got through the 3 barrels of Salopian Hop Twister - the first one without me and they knew I was away, the real rub, my mate delivered that beer to that pub at my request and I was given a tiny sample of the first and best barrel last thing on Thursday night before they put it on next day when I'd already warned again that I was away Friday and Saturday - there's just no respect
N Atkins

Yes we agree Bob electricity is very dangerous and only fully competent people should medal with it, I think that was the point I was making more than anything else. We will have to disagree on what is required to trip a 30ma RCD however. Even touching phase and nuetral will trip the RCD because we have a parrallel circuit to earth via the body.
That is irrelevent however as the point we both agree upon is the need for competent care.
Dave how anyone choses to wire up a circuit is entirely up to them. we do have guidlines and best practice however and most installers will stick to those principles.

I must just restate it is a dangerous medium and I hope all will treat with respect and care, as I would hope we do with brakes.

Bob Ken's first wife was called Valerie and died from electric shock due to a faulty socket. Yes it was fictional but at that time women were using 2 pin adapters to plug irons into lamp fittings!!!!,(my mother used to do it) thank goodness we have moved forward.

I am pleased I have never had a shock off 600V whether DC or AC, all the cases I have been made aware of have sadly ended in death of the individual, I work with 24 to 11KV daily and I make sure that above 110V I do not take chances easier said than done.
Robert (Bob) Midget Turbo

How did this tread become about carbon monoxide...just open a window, im sure you will survive without issurs,

unless you get bitten on the juggular vain by a brown reacluse spider that escaped into the bedroom thur the window jamb

I knew an old lady that used a mouse to catch the spider that caught caught the roach that at the fly...perhaps she will die
Prop

Bob,

Your mother was very fortunate in possessing such an advanced electric iron!

My mother had to heat her iron on top of a primus stove, she would wet the tip of her finger before touching the sole of the iron to make sure it was hot enough.

Dave
D MATTHEWS

LOL

or should that god help us!

Just realised I meant meddle and not medal!
Robert (Bob) Midget Turbo

Prop, cabon monoxide is colourless, I think entirely tatseless and smelless in itself, and it sends you to sleep (hence the popularity of the hose from the exhaust) so inocent (and otherwise) victims don't always get the chance to open a window

only mentioned for its unseen danger similar to faulty wiring

I well remember selling round pin plugs in mid-70s then they came back for commercial use

as Bob said electricians can wire as they please and DIYers any how so lots of people can easily make mistakes with existing wiring unless they thorough check and that not to mention how people misuse electric and gas appliances
N Atkins

I had an electrician colleague who worked on live panels from time to time, and he reckoned it was good to work with arms down and elbows bent, because electricity doesn't take corners well.
Nick

I think you'll find most electricians just book the call and don't actually go into the building :)

elecmagicians I call those

look up the old joke about God checking an electrician's time sheet
N Atkins

I'm an electrician, its sound to me he has given you a sustained supply to cover possible future options (sorry if already covered I've not read the full thread)

You can either have a normal switched light and put the brown in a connector

Have a PIR controlled light using brown as the supply black in a connector

Or many fittings allow both, so you can use as a PIR or an overide, so swithed and perminant live are both used (separate live terminals)

The white you describe should be Grey
as it's probably faded, the new 3c+ Earth harmonised colours are Brown, Black, Grey, most of us use the Grey as a neutral as the industry wanted to get away from the black as a neutral.


If you are on harmonised colours the chances are you should be 17th edition compliant,therefore the circuit will be protected by RCD or RCBO, both of which will activate on earth leakage (and will trip on neutral to earth) you would have got a belt as you became (but presumable) the earth but as you were probably on steps and didnt cause a short circuit you became it for that split second, unless a passage to earth, overcurrent or short circuit a mcb or RCBO will not trip, hence why it is so importnat to have systems correctly earthed and protected by an adaquate device.

Jim Stewart

Sorry, to reiterate above get your man back to do it anyway, just offering advise on what set up he'd left you :)
Jim Stewart

>If you are on harmonised colours the chances are you should be 17th edition compliant,therefore the circuit will be protected by RCD or RCBO

only if the new light is a new circuit. the rules allow you to fit a new appliance to a circuit (within some bounds) and this can be on the new colours and hence not on a RCD/RCBO.


Do you know why the shift from using black for netural? I always thought that the obvious way to wire three phase for switches was:

Old:
Red -> Live
Blue -> Neutral
Yellow -> switched

Red -> live
Black -> Neutral



And its allegory
Brown -> live
Black -> Neutal
Grey -> switched

Brown -> live
Blue -> neutral


That way, black or blue is always neutral.


To identify what is going on with wires, you should probably test (colour) -> Earth to avoid "this looks cold" when measuring between a colour you assume to be neutral and or a colour you assume to be live. Of course, that doesn't stop the earth from being disconnected in the cable run (which I have seen done by a "professional" - because the light on the end of the twin and earth was double insulated)
Will Munns

Will, yes I agree if the circuit was added or just an extension of.

Our ECA/ NECEIC directive was called "de-neutralising the black"

It was a deliberate action to move away from the old neutral which as you correctly state is black, they prefer to oversleave or identify the gray as an alternative (not my choice to be honest, but again they are trying to create some commonality I suppose, similar as every spark would use different colours for the common on a two way switch)

I know the three colours are all "line" colours, but in three phase circuits obviously black is a line conductor too (silly enough as was blue), all came from Europe from what I gather.
Jim Stewart

Thanks Jim. That gives me confidence, because I did put the brown away, and am running it as a normally switched fitting on the black switched live. It works OK.

But not being up with electrical customs, I was surprised to find black live.

I reached your conclusion by 'if this, then that' logic, having tested the four ends.

Haven't heard from you for a long time, Will. But then, I haven't been here much.

Nick

Hi Nick,
Yes, I disappeared about 2 years ago to travel Europe in a 78 VW. since getting back to work in November I have been working full on fixing up a house (apparently I get a garage built to my specifications as a prize after all my hard work).

Jim,

How binding is the directive - I don't remember reading anything in the reg WRT to it

With new 3 phase installs, do you still get red, blue, and yellow phases? I assume that there is a standard to which old colour gets connected to which new
Will Munns

Hi Will

Phase colours are
Brown
Black
Grey

Nuetral is
Blue

Earth is
Green/Yellow

Therefore

3 phase are Brown Black Grey connecting to Red yellow blue accordingly

Many people are struggling to note a difference between phase colours?

You can not buy old colours anymore! and new installations after (was it 2006?) must be in new colours or connected to old installations as described above with relevent paperwork located in the distboard!
Bob Turbo Midget England

Sorry to bump the thread again, but I can't get online as much... Bob is right, and the directive was a "suggestive measure" and has not been incorporated into BS7671 (The IEE regs)

The logic I can only apply is when using old three phase red/yellow/blue, it was logic to use the blue in single phase as a neutral as it was in a flex anyway, BUT now black under any new system is never a neutral, thats why they are drilling it as a "line" only.

That all said, BS 7671 does state "correct identification of conductors" so theoretically Nicks spark should have left brown, black with brown sleeve, and grey with blue sleeve, much like a switch wire should either be twin brown or blue oversleeved with brown.

All projects we work on (when single phase), ECA companies appear to be applying the common rule of using the grey as neutral with blue sleeving.

Nick, your testing proved the above, (sorry long winded response) but you have your desired control.

Jim Stewart

Hi Jim,
Good to see you on here again.
Hope all is well with you.

Guy
Guy

Hi Guy, thank you yes and you?

Sooty is still "under construction" had a few "upheavals" over the last couple of years as you do, managed to get my log garage finished for her, so plan to bring her home this year to work on.


Jim Stewart

This thread was discussed between 25/06/2011 and 05/07/2011

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