New wylex mini RCBO

A lot of RCBOs were made with just L & N and no E required. An RCD of any flavour (RCCB, RCBO, SRCD etc etc) do not require an earth to monitor. That`s whay we call them Residual Current Devives and not Earth Leakage Devices although in practice they are often detecting Residue to confirm leakage.

A lot of RCBOs then gained an earth lead simply to ensure power across the detecting/tripping part of the device in the event that N was lost. I suppose a big capactor could do a similar job by ensuring that an RCBO would continue to trip if power was lost before or just after the trip cycle was initiated. Such a capacitor would be relatively big to hold enough charge to complete that so the earthlead as an alternative way to give a voltage until L disconnected seems to be the approach.

That`s my take on it.

The wiser on here(Mapj1/DaveZ/Gkenyon/JP  etc) might l give a better and correct explanatiom.

Ebee has explained well, but there are two points to make. These are "electronic" RCBOs and therefore require power at all times. Whether the "Earth" connection is to prevent loss of power if the neutral is lost (where have I heard that before?), is not something I have looked at (yet) in my RCD survey. You are right that if neutral is lost, there is a potential danger that a person could contact the phase conductor and still receive a shock. However, it would be dangerous (particularly in a TT installation) if the Earth were expected to provide any significant current as this would develop a voltage across the electrode resistance or Ze on all exposed conductive parts and bonded metalwork to real Earth, exactly what we are attempting to sense and disconnect. Consider a PME install, using the local Earth is useless as this is still the supply neutral, which is possibly broken, therefore no effect!


I think this wire may be for EMC reduction purposes, do the instructions say anything useful?

There are reports whereby the new AFDD versions of these devices are causing adjacent devices to trip when the RCD conponant of the device connected to the faulty circuit is triggered by a fault. Cause not yet known.

whjohnson:

There are reports whereby the new AFDD versions of these devices are causing adjacent devices to trip when the RCD conponant of the device connected to the faulty circuit is triggered by a fault. Cause not yet known

The MEM RCD pods that clip onto the MCBs to convert them to RCBOs have no real physical connection, the pod just sits on top of the MCB but can fire the MCB off as required.


I presume the MEM RCD pod uses a magnetic pulse to fire the MCB off and have often wondered if it could possibly fire an adjoining MCB off as well as the intended target?


Andy B.

https://www.cef.co.uk/catalogue/products/394584-30ma-230v-ac-field-fittable-residual-current-unit-grey

Hmm, interesting Sparkingchip. Glad you mentioned it

Life is full of little mysteries.

Actually I was referring specifically to the new Wylex AFDD/RCD/MCB combi offerings. It seems that they invoke 'sympathetic trips' on adjacent devices when the device connected to a faulty circuit trips out on what is identified as a trip of the RCD element.

It sounds likI would guess it’s due to a magnetic pulse.

The idea of a no-contact  pod is interesting,  given that it must connect to L and N to get power, and after the usual 'shunt trip' methods of push rods and so on, surely the next easiest way to fire the MCB is to create an overload - just draw a short duration L-N burst via a connection of an few ohms.

I must admit, I'd be a bit surprised, my first expectation would be a push rod, but I can see a non-mechanical method has attractions.


Unless the MCBs have been designed with the magnetic  core to the MCB actuator in some way exposed, it would be very hard (i.e. you would need  far need more amp turns) to generate magnetic flux from a distance, than you could generate by just  drawing  large current through  the internal coil that was already optimally wound around the actuator core in the MCB, to sense the live current.

Clearly if you do this and the MCB does not trip then something melts, but a fusible link in the RCD pod would not be beyond the bounds of possibility for such occasions, as the MCB assembly  would then need replacing anyway.

Magnetic pulse generation, despite Star Trek and others, is something that gets rapidly harder with distance, and to get field into a closed coil from the outside is as hard as detecting the field leakage from inside out  - if only a few %  of the flux strength gets out, then the coupling factor for getting your impulse in is similarly poor ...

Mind you, if MCB firing is by pulling  a large current then a voltage twitch that operates the neighbours is quite likely, no close proximity magnetic coupling needed

Mike.

The neutral is wired through the pod, but the live just passes through a hole in it to the MCB terminal.