Simultaneously accessible parts are conductors or conductive parts which can be touched simultaneously by a person or, where applicable, by livestock.

Supplementary bonding is the practice of connecting two conductive simultaneously accessible parts together to reduce the potential difference between the parts.

In a home installation this area is typically the bathroom, or any other room containing a bath or shower.

All extraneous conductive parts in zones 0, 1 and 2 must be connected by supplementary bonding conductors to the protective conductors of exposed conductive parts in these zones.