BS EN 61009-1 defines ‘pole’ as: ‘that part of an RCBO associated exclusively with one electrically separated conducting path of its main circuit provided with contacts intended to connect and disconnect the main circuit itself and excluding those portions which provide a means for mounting and operating poles together’.

Further, BS EN 61009-1 defines the ‘overcurrent protected pole’ as one which is, ‘…provided with an overcurrent release…’. The ‘switched neutral pole’ is given as: ‘pole only intended to switch the neutral and not intended to have short-circuit capacity’.

Taking all definitions into account, it is important to recognise what this means when a manufacturer defines a product as single-pole (SP), single-pole and neutral (SP&N) and double-pole (DP).

•             SP – a device having no connection point for the neutral conductor. The circuit neutral conductor will be connected to the common neutral bar. When the RCBO is switched ON or OFF the neutral will remain connected in circuit and only the line conductor will open or close.

•             SP&N – a device having a connection point for the line and neutral conductors and typically taking up two ways on the distribution board. When the RCBO is switched ON or OFF both the line and neutral conductor will open or close. However, the neutral connection will not have short-circuit capacity.

•             DP – a device having a connection point for the line and neutral conductors and will typically take up two ways on the distribution board. When the RCBO is switched ON or OFF both the line and neutral conductor will open or close. The neutral connection will have short-circuit capacity.

Being a combination of circuit-breaker and RCD, RCBOs may be selected for use for both overcurrent protection and additional protection, and recognising the benefits of an RCBO as:

•             Individual additional protection and control of final circuits,

•             Easier to fault find,

•             Less chance of unwanted operation.

To find out more about RCBOs and other protective devices go to https://www.youtube.com/watch?v=Hn9Mz7v58pg where Jake Green and Tim Benstead discuss how protective devices have evolved over the years.