I have little detailed knowledge of what ESQCR says (and actually didn't think it covered details of what happens within an electrical installation?) - but if what you say is true, the I would ask the authors of ESQCR the same thing as I asked you (without yet getting a reply), namely "in what sense is it (electrically) 'unsafe'? "
Using a double pole swich for outside light
- Thread starter TNDU
- Start date
Taking a quick look (IANAL, I may well have missed something(
Many of the regulations in the ESCQR are scoped to generators or distributors, but there seems to be at least one regulation that is scoped explicitly to consumers , and some of the regulations relating to underground and overhead cables seem to be applicable to everyone.
I presume reistard is refering to 8.(4) from the ESQCR
The question would then be does using the earth wire to feed an indicator constitute "combining the neutral and protective functions".
Connecting loads to the Earth conductor can create a couple of potential hazards.
The first is the risk of overloading, since earth conductors are not designed to support normal load currents.
The second is the risk that in the event of the earth becoming disconnected currents flowing in the earth conductor could be diverted into someone touching metalwork connected to the earth conductor. Of course "leakage" currents can also cause this, but leakage impedances are hoepfully somewhat balanced between live and neutral, so the voltage developed on the disconnected conductor would only be half the supply voltage, whereas with a load the voltage developed would be the full supply voltage.
Obviously the first risk is neglitable with a load as tiny as a neon indicator. It would take over a thousand of them to overload the earth conductor in even the smallest size of TP&E. The second though does seem like it could potentially be a real risk.
Last edited:
- Joined
- 18 Apr 2022
- Messages
- 5,089
- Reaction score
- 622
- Country
IMO no.
Yes, that would seem quite likely.
I suppose there is some scope for debate about that but, for what it's worth, my initial inclination would be to say 'no'.
In the context we are discussing, in the absence of faults (against which there should be protection), and as you go on to say, the current we are talking about is 'extremely negligible'.
Could you perhaps be a little more explicit in describing the sort of scenarios you are contemplating? Thanks.
I would say this ... that, although I don't offer this any any 'justification', in the eyes of someone not prepared to do it 'properly' (install a new neutral conductor in some way), the only alternative to leaving the CPC as a CPC and using it as a return path for the neon, would be to re-purpose the ('bare' if T+E) CPC as a neutral conductor (maybe sleeving it at terminations, such that there was no longer a CPC. If that were the 'perceived 'choice', then I think there are multiple reasons for believing that the latter course would be the less desirable.
There is at least one place in my house where this has been done (not by me!) to provide functionality of a neon in a wall thermostat fed with T+E. I have been 'intending' to sort that out for very many years, but have never got around to doing it - and I have to say that I loose absolutely no sleep over it not yet having been addressed!
Lets assume for now the switch has a metal plate.
Now suppose that the earth wire to the switch becomes disconnected from the earthing system, but the neon is still connected to the switch plate.
Now the current flowing through the neon has "nowhere to go". The switch plate becomes "live". If this were a resistive load it would be at the full 230V, but neons are a bit weird, so I'm not sure the exact voltage is so well-defined.
When a user touches the switch plate at the same time as something that is actually earthed, then current flows through the series combination of that person's body and the neon indicator.
What I'm not sure of is whether a typical indicator neon will pass enough current to actually give someone a shock. Neon screwdrivers are designed to intentionally pass current through a person's body but I don't know if they use larger resistor values than typical indicator neons (and some switches nowadays use LEDs instead of neons).
If the switch does not have a metal plate then a break in the wire immediately feeding the switch won't pose a hazard, but a break further back in the system could do so.
Now suppose that the earth wire to the switch becomes disconnected from the earthing system, but the neon is still connected to the switch plate.
Now the current flowing through the neon has "nowhere to go". The switch plate becomes "live". If this were a resistive load it would be at the full 230V, but neons are a bit weird, so I'm not sure the exact voltage is so well-defined.
When a user touches the switch plate at the same time as something that is actually earthed, then current flows through the series combination of that person's body and the neon indicator.
What I'm not sure of is whether a typical indicator neon will pass enough current to actually give someone a shock. Neon screwdrivers are designed to intentionally pass current through a person's body but I don't know if they use larger resistor values than typical indicator neons (and some switches nowadays use LEDs instead of neons).
If the switch does not have a metal plate then a break in the wire immediately feeding the switch won't pose a hazard, but a break further back in the system could do so.
OK, I understand. Thanks. As you say, in that situation some current would flow through them if they found something earthed to toch at the same time as touching that 'live' plate. In any event, as you go on to say ...
Every one I've ever taken apart has had a series resistor of at least 100 kΩ - so, if one assumes around 90V 'running current' across the neon (and more to 'strike' it), it would probably be less than 1.5 mA,- certainly not enough to do any harm to (or even necessary be felt by) virtually all people.
I don't know what the situation is (current drawn by) the modern LED equivalents, but I suspect that it may well be similar.
Maybe because it's getting late at night (or I'm getting older!) but I think I need a bit of 'clarification' of that one
DIYnot Local
Staff member
If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.
Select the supplier or trade you require, enter your location to begin your search.
Are you a trade or supplier? You can create your listing free at DIYnot Local
