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..

 

[Dillb]

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.

 

[Marvo]

Is there actually a UK reg forbidding this? I'd be interested to hear how it's worded.

The CPC is both functional and protective and often circuit elements in many appliances and light fittings such as noise suppressors, surge arrestors etc already use the CPC for their functionality. A neon indicator would be over a megaohm so the load current would be less than a quarter of a miliamp, this would be less than many suppression circuits might leak to earth.

 

[Dillb]

Yes BS7671 states that a conductor identified as G/Y can only be used as a earthing conductor, not got the book to hand to state ref number though.

Functional conductors are identified as cream, although some RCBOs do come with a G/Y flying lead

 

[marconi]

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

 

[Deleted member 26818]

Yes BS7671 states that a conductor identified as G/Y can only be used as a earthing conductor, not got the book to hand to state ref number though.

Functional conductors are identified as cream, although some RCBOs do come with a G/Y flying lead

Change the colour from G/Y to cream.

 

[a-z electrics]

The CPC is both functional and protective and often circuit elements in many appliances and light fittings such as noise suppressors, surge arrestors etc already use the CPC for their functionality. A neon indicator would be over a megaohm so the load current would be less than a quarter of a miliamp, this would be less than many suppression circuits might leak to earth.

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

 

[telectrix]

you could, but it's not recommended. marconi gave you the solution. in post #5

 

[Rocboni]

Can you not just pull a 4 core in with the old 3 core?

 

[a-z electrics]

Can you not just pull a 4 core in with the old 3 core?

not that simple Im afraid.. its about a 25 m fun..

 

[a-z electrics]

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

That looks interesting Marconi, i shall try that. Many thanks..

 

[a-z electrics]

Is there actually a UK reg forbidding this? I'd be interested to hear how it's worded.

The CPC is both functional and protective and often circuit elements in many appliances and light fittings such as noise suppressors, surge arrestors etc already use the CPC for their functionality. A neon indicator would be over a megaohm so the load current would be less than a quarter of a miliamp, this would be less than many suppression circuits might leak to earth.

I shall try that too, just to see! oh this is fun,...

 

[a-z electrics]

- 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.

I also have a neon dp switch, so i could just replace the neon with the led and just use it as a sp switch... save drilling a hole.

 

[a-z electrics]

Yes BS7671 states that a conductor identified as G/Y can only be used as a earthing conductor, not got the book to hand to state ref number though.

Functional conductors are identified as cream, although some RCBOs do come with a G/Y flying lead

Well there's a contradiction straight away!

 

[Dillb]

Well there's a contradiction straight away!

You expect anything less from BS7671 and the manufacturers

 

[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?