Rcbo white lead

Keep them tightly secured in the earth bar to avoid touching them and getting a shock?


 Andy B.


(I suspect you have something else in mind)

I always thought the white lead was the reference earth cable that enables the monitoring of the voltage to the neutral. Wire into the earth bar. (I haven't got a clue what else you have in mind)

Yes Andy, just wanted to know how the white lead connects with neutral when it becomes open circuit.

I am not very up to date or confident on this, but  the problem is that RCD/RCBOs that use an electronic means to fire the coil - see     The application circuit in this rather US centric data sheet    This design has no earth tail, and if N fails, then there is a problem, as to fire the trip, there has to be somewhere for the firing current to go. I have seen, but have no copy of, a design that looked rather like a diode bridge for 3 phase, that  allowed a firing supply to be created to power the sensor and actuator parts, by rectifying between  L, N and E in such a way that if any two wires had voltage between the then the DC supply to fire the trip would be created.

I suspect that perhaps with current limiting fusible resistors this is the sort of thing inside these devices.

There are other devices that do not detect a loss of neutral where it is just filtering components to the earth to reduce misfiring on transients.

Some makers statements to partly back that up. and  fig 2 in this patent

as an aside, this industry guidance https://www.electricalsafetyfirst.org.uk/media/1258/consumer-unit-connections.pdf says;

 The functional earth of an RCBO should be placed in the same terminal as the associated protective conductor and should be placed behind the protective conductor to minimise the risk of damage

The circuit is arranged with diodes to prevent any direct connection from N to E... there's a small chance of the diodes shorting I suppose, but the size of the FE wire would mean it would blow like a fuse before any substantial current could pass. It is much the same as say, on a DC supply, allowing a device to use either 4.5v from alkaline cells or 5.0v from usb, using diodes to prevent the 5v supply trying to charge the alkalines.

I`ve always made the assumption that you`ve essentially got two power supplies for the electronics to fire.

Say a bridge rectifier from Ph and N for  instance - or alternatively a half wave diode, charging a cap.

Likewise second power supply from Ph to PE.

Both connected via a diode. and probably charging a resovoir cap.

Lose either N or PE and you still got one power supply to the electronics.

But, like I said, that`s my assumption