A circuit for displaying correct Live-Neutral-Earth with LEDs. Also fault conditions.

Thread Starter


Joined Feb 26, 2017
Hi All,

I am designing a small single phase power distribution board for stage use.
A 63A CeeForm (IEC 60309) inlet will supply multiple 16A CeeForm outlets.
In series between the I/O will be a dual pole breaker > a RCB > then individual MCB's for the 16A outlets.
There will also be a panel meter displaying voltage and current.

On some proprietary distro's of this sort there are also 3 LED's displaying:
  • Correct connection of L-N-E
  • L-N Reversed
  • Neutral Fault
  • Earth Fault
Like this: http://kelseyacoustics.co.uk/produc...tribution-units-with-13a-sockets-on-the-rear/

I'm researching a circuit that can achieve the above. Can anyone please point me in the right direction.

BTW: I'm UK based, so single phase supplies are 230V AC.

Many thanks.

Thread Starter


Joined Feb 26, 2017
Hi Albert,
I am aware of these testers but thought is was a bit of a cop out and wouldn't be as/look as professional as an integrated solution.


Joined Sep 4, 2010
its just a matter of voltages...
As is your other problem with built in solution, it is likely to fail a PAT test which it must have for commercial use along with a CE mark.
You can self cert for CE but its risky as an individual, what quals do you have?

I have looked at doing this myself and dropped the idea as impractical and potentally dangerious...
this shows a circuit copied from a comercial unit, it works on the face of it but there are serious issues with the aproach, see the text it explains better than I could in a week.

On the pluss side a clever arrangenent of resistive bridges can detect some issues and that may save you but there is a huge minus. It isnt going to protect you from the kinds of things that can and do happen when cables ger crushed and plugs get changed in a hurry but folk that simply shouldnt be changing them.

Please dont be offended I am not suggesting you are ill informed or should not be messing with this stuff, after all I have no idea about your skill base. However I do know enough about my skill base to know that these sort of devices are anything but definative with respect to their ability to indicate a safe condition relyably in all circumstances and wen all said and done some circumstances just isnt going to cut it.

There are devices, usually controlled by microprocessors that can and do perform tests on live circuits. They often use very short duration high current pulses to directly measure impedance and can detect isolated live conductors using the dielectric properties of the air around them but even those need careful handling to be cirtain the results are a good indication of a fully safe condition.

Can what you want be done... probably, should you do it with a DIY device and then effectivly take responcibility for the safety of who knows how many complete strangers, many of which probably have not the slightest clue what they are doing... I would suggest a catagorical NO.
In fact I wouldnt even recomend plugging in an off the shelf unit... read the manuafcturers disclaimers.

I agree it is an interesting little problem but I would recomend you exersize caution with respect to where you play with it.

I will not be preaching about this and I mean no disrespect at all but please be careful taking responcibility for othrs and even yourself if you are not 100% sure that you know what you are doing and what your circuit is capable/incapable of detecting.

Sorry to be blunt,
be safe and have fun,
Last edited:

ian field

Joined Oct 27, 2012
The only trouble with these mains neon testers, is they can't show Neutral and Earth reversal.

View attachment 126059
N & E shorted will trip the ELCB if there's enough load elsewhere to develop a voltage gradient on the neutral ring. Reversal will send the return current down the safety earth instead of the return current sensing - the ELCB will trip much more reliably.

A stage panel implies various stage hands that will be using the equipment - approved PAT testing may even be a legal requirement.

The instruments aren't cheap - but it should be possible to find one that isn't mind blowingly expensive.