Construction sites ā€“ RCBOs and double pole switching of outlets

Above: Switching active only (left) | Switching active and neutral (right) 

The requirements for construction site wiring are detailed in Australian Standard AS/NZS 3012:2010 which is available for all members to view here on our Technical Knowledge Base (TKB). 

By definition, construction site wiring is defined as “wiring on a site where construction or demolition work is being undertaken”. It does not include site wiring that forms part of the permanent electrical installation and is wiring that is intended to be removed at the completion of the construction work. Parts of the permanent installation that are used to support or supply construction wiring are, however, not excluded from this standard.

There has been some confusion as to where double pole switching is required on RCDs and socket outlets. Clause of AS/NZS 3012 requires that all final sub-circuits originating from a switchboard are protected by an RCD with a maximum rated residual current of 30 mA. These RCDs must operate in all active and neutral conductors (the neutral must be switched).

Exceptions to this rule include where the circuit supplies equipment where safe mechanical operation is at risk (including cranes and lifts).

Electrical workers need to be aware that with the advent of single pole RCBOs, not all devices are switching the neutral. On most brands there is a wiring diagram on the side of the unit which clearly shows whether the neutral is switched, or alternatively, that testing should be undertaken to prove double pole switching. Electrical workers must check that the RCBOs they are installing are double pole to avoid non-compliance.

Socket outlets installed on construction sites only require double pole switching where they are part of a portable socket assembly, the outlet is connected via a plug and cord or where their originating switchboard is plug-in. Outlets that have an integral switch that operates when the plug-top is inserted and switched off when it is removed, are regarded as double pole and hence are acceptable. 

Where the socket outlets are supplied direct from permanent or hard wired (non-plug-in) switchboards, they may be single pole, however their circuit protecting RCD/ RCBO must be double pole.