Indicator switch with no neutral?

[a-z electrics]

Think i may be onto a loser here but is it possible to wire a simple one way switch and have some sort of indicator like a neon WITHOUT having a neutral? Its for the water pump to push hot water when required to kitchen tap (it's a long way from cylinder). There is already power at the pump, just need a switched live return.
I have a 3 core flex coming from the pump but the switch has to match the other fittings in kitchen and is metal fascia, hence needs a cpc! So my 3 wires are used up..
It may be possible to link a cpc from an adjacent skt but it's all newly plastered.. I know MK do a surround thing with a little led requiring no neutral but this is lit when OFF.
I assume neon grid modules need a neutral? I have a DP neon switch which was bought for it but obviously this needs a neutral.
Worst case is to just use an ordinary rocker switch with no indication but thought I'd ask.
Thanks..

 

[Marvo]

Do you mean I cd wire a neon across s/L and cpc?

Yes, I was suggesting the neon between the switched live and the CPC. Electrically speaking I wouldn't really see a problem with such a small current flow and many appliances and electonic power supplies already regularly have components wired between the current carrying conductors of the supply and the CPC which introduce small leakage currents into the circuit..... I know it's not ideal and can even understand it being classed as bad prictice, the only thing I'm not sure about is whether the UK regs explicitly take it off the table as an option.

 

[johnduffell]

You can over sleeve green/yellow with another colour and use it differently in a multi core, except for a single cable.
The problem with t&e is the lack of insulation in the cpc. You would need insulation to mains voltage to use it for anything else.
Also even if the fitting doesn't need a cpc, you still need to provide one to every termination, so you'd still need one from somewhere.

 

[johnduffell]

Re used the cpc to power a very small load

, the only thing I'm not sure about is whether the UK regs explicitly take it off the table as an option.

Depends if you are using it as a combined neutral and earth, which is forbidden, or just for filtering.
I'd say technically the latter as you are connecting a load, but I'd not be overly concerned re the current.

 

[Lucien Nunes]

I like Marconi's solution but wanted to add something about running a neon to earth. As per Marvo, there are filtering components in electronic devices connected from L to CPC, which are legitimate and necessary to combat radio interference. However they are required to meet certain constructional standards which you neon-with-current-limiting-resistor indicator lamp may not meet because it was not specced to run to earth.

If I had to do this, I would use a class Y capacitor as an additional current-limiting measure - these are permitted between L & CPC and also L and exposed metal of class II equipment, as they are self-healing and unlikely to fail short-circuit. FWIW If the indicator current is less than 0.25mA then even in the event of CPC failure, the current available to the touch is below the prescribed limit for class II equipment. But whatever is limiting the current must have proven durability and integrity, just like cable insulation.

 

[Colin33]

What you could do is sense the flow of the alternating current of the motor when the pump is turned on by the switch instead of sensing the voltage applied to the motor. What you would need is a current transformer connected to a low voltage LED. A number of manufacturers make a ready made current transformer connected to an LED - all you would have to do is thread the load's line conductor through the current transformer's hole and drill a small hole in the switch plate to push the LED lamp through. If the magnetic field from one pass of the load line conductor through the CT is insufficient to light the LED then all you have to do is loop it though a second, third or fourth time - obviously there is a limit due to the CT's hole size and the diameter of the wire. The one I thought you might try is CR Magnetics CR2550-R:

http://www.crmagnetics.com/Assets/ProductPDFs/2550.pdf

which will light the LED at 0.75Amps AC for one pass through the 9mm hole. You could buy other colour LEDs.

They can be bought from:

CR Magnetics CR2550-R - https://octopart.com/cr2550-r-cr+magnetics-1186351

I have a similar situation whereby I need to light an indicator lamp when the outside lights are left on. Problem is, the outside lights comprise of 2 x 5w GU10's. I assume this means passing the wire through the hole around 18 times, is that correct, and doable with a 1mm cable?

 

[marconi]

I am just heading out the door but you are right that more turns will be required for the lower load current of your application. To light the LED requires 0.75 AmpTurns of alternating magnetic flux. As long as the product of load current multiplied by number of turns equals 0.75Aturns then the LED will illuminate.

 

[marconi]

"Colin33, post: 1410887, member: 18528"]I have a similar situation whereby I need to light an indicator lamp when the outside lights are left on. Problem is, the outside lights comprise of 2 x 5w GU10's. I assume this means passing the wire through the hole around 18 times, is that correct, and doable with a 1mm cable?[/I]

The CT's hole is 9mm diameter. The diameter figure I turn up for solid single core insulated 1mm2 is in the range 2.1 to 2.5mm. I reckon this will pass through at most 12-13 times. So, you you will have to use a lower csa flex - say 0.5 mm2- and protect it with a 1 A fuse and mark up this maximum fuse size - see:

1 Amp Plug Fuse - BS1362 - https://www.tlc-direct.co.uk/Products/TLF1.html

http://www.batt.co.uk/upload/files/4f3a_1231500485.pdf

If it was me, I'd see if 12 turns of 1 mm2 provided sufficient LED illumination and if not then use the 0.5mm2 flex and 1A fuse method.

Sorry for the delay in answering this last part of your post.

 

[Colin33]

The CT's hole is 9mm diameter. The diameter figure I turn up for solid single core insulated 1mm2 is in the range 2.1 to 2.5mm. I reckon this will pass through at most 12-13 times. So, you you will have to use a lower csa flex - say 0.5 mm2- and protect it with a 1 A fuse and mark up this maximum fuse size - see:

1 Amp Plug Fuse - BS1362 - https://www.tlc-direct.co.uk/Products/TLF1.html

http://www.batt.co.uk/upload/files/4f3a_1231500485.pdf

If it was me, I'd see if 12 turns of 1 mm2 provided sufficient LED illumination and if not then use the 0.5mm2 flex and 1A fuse method.

Sorry for the delay in answering this last part of your post.

Thanks, I'll give this a go. I was hoping to get this LED into the MK grid module ( Which I'd bought to do the job before realising the lack of neutral) but I think that may prove impossible. I'm wondering how neatly the led can be installed into part of the switch backplate, has anyone else done this before?

 

[marconi]

Colin33 - did you have a successful conclusion to this problem please?

(Sorry to nag because you are no doubt busy but the EF love to know the outcome of threads after advice is offered otherwise it is all theory - and we are practical people who want to know what works or not).

 

[Colin33]

Colin33 - did you have a successful conclusion to this problem please?

(Sorry to nag because you are no doubt busy but the EF love to know the outcome of threads after advice is offered otherwise it is all theory - and we are practical people who want to know what works or not).

Hi marconi, the client has been away so I've only recently been able to discuss the options with him. He has decided to leave things as they are for now, and hopes that the new brighter LED lamps I've put in his outside lights will make it more obvious if/when they are inadvertently left on. I'm rather disappointed because I was looking forward to experimenting with the current sensor!
I thank you and everyone else for the valuable input

 

[integrationdan]

Using a CPC for anything other than it’s intended use is not allowed on BS7671, you could look at using a LED wired in series in your circuit.

Wrong - do people think that a piece of conductive material with green/yellow indicator sleeving works differently in any way than the other conductors?

It is a metal, the colour is only an indicator put there by the manufacturer for our convenience. If you then decide to place brown/blue/grey sleeving atop of the green/yellow, what possible difference does it make.

Earth core has not been bestowed with some magical curse, it is simple copper with a coloured cover. No decent Engineer would ever consider it any other way. The only consideration might be the reduced C.S.A. if it's PVC/PVC flat twin and skin.

In fact if you wanted to use g/y as line, blue as CPC and brown as neutral - with a good reason, there is nothing stopping you. The regs only state they should be clearly identified at access points and terminations. This could be the word LIVE, letter L, the word LINE, or a coloured section of sleeving.

AND... the regs are a guide, used to supplement/inform. We as qualified Engineers can deviate any way we choose, as long as it is safe, and justifiable.

Danny

 

[littlespark]

Wrong - do people think that a piece of conductive material with green/yellow indicator sleeving works differently in any way than the other conductors?

It is a metal, the colour is only an indicator put there by the manufacturer for our convenience. If you then decide to place brown/blue/grey sleeving atop of the green/yellow, what possible difference does it make.

Earth core has not been bestowed with some magical curse, it is simple copper with a coloured cover. No decent Engineer would ever consider it any other way. The only consideration might be the reduced C.S.A. if it's PVC/PVC flat twin and skin.

In fact if you wanted to use g/y as line, blue as CPC and brown as neutral - with a good reason, there is nothing stopping you. The regs only state they should be clearly identified at access points and terminations. This could be the word LIVE, letter L, the word LINE, or a coloured section of sleeving.

AND... the regs are a guide, used to supplement/inform. We as qualified Engineers can deviate any way we choose, as long as it is safe, and justifiable.

Danny

Every cable must have a cpc in it.

Over sleeving the g/y to use it as a live conductor removes it as a cpc, and that cable no longer has one.
It doesn’t matter how short that cable is.

 

[DPG]

Wrong - do people think that a piece of conductive material with green/yellow indicator sleeving works differently in any way than the other conductors?

It is a metal, the colour is only an indicator put there by the manufacturer for our convenience. If you then decide to place brown/blue/grey sleeving atop of the green/yellow, what possible difference does it make.

Earth core has not been bestowed with some magical curse, it is simple copper with a coloured cover. No decent Engineer would ever consider it any other way. The only consideration might be the reduced C.S.A. if it's PVC/PVC flat twin and skin.

In fact if you wanted to use g/y as line, blue as CPC and brown as neutral - with a good reason, there is nothing stopping you. The regs only state they should be clearly identified at access points and terminations. This could be the word LIVE, letter L, the word LINE, or a coloured section of sleeving.

AND... the regs are a guide, used to supplement/inform. We as qualified Engineers can deviate any way we choose, as long as it is safe, and justifiable.

Danny

I think we're all well aware of the electrical properties of copper, regardless of the plastic covering it has. The issue is the identification, especially if the little bit of brown sleeving falls of at some point and someone assumes the grn/yellow wire is safe to touch.

The regs offer safe guidance in this case.

 

[loz2754]

Every cable must have a cpc in it.

Over sleeving the g/y to use it as a live conductor removes it as a cpc, and that cable no longer has one.
It doesn’t matter how short that cable is.

Every final circuit must have a CPC, but it doesn't necessarily mean every cable has to.

 

[davesparks]

Every cable must have a cpc in it.

Not quite, every point of termination must have a CPC at it, not every cable.