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.
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.
