Editing Residual-current device (section)

===Number of poles and pole terminology===
The number of poles represents the number of conductors that are interrupted when a fault condition occurs. RCDs used on single-phase AC supplies (two current paths), such as domestic power, are usually one- or two-pole designs, also known as [[single-pole|single-]] and [[double-pole]]. A single-pole RCD interrupts only the energized conductor, while a double-pole RCD interrupts both the energized and return conductors. (In a single-pole RCD, the return conductor is usually anticipated to be at [[ground potential]] at all times and therefore safe on its own).

RCDs with three or more poles can be used on three-phase AC supplies (three current paths) or to disconnect the neutral conductor as well, with four-pole RCDs used to interrupt three-phase and neutral supplies. Specially designed RCDs can also be used with both AC and DC power distribution systems.

The following terms are sometimes used to describe the manner in which conductors are connected and disconnected by an RCD:
:* Single-pole or one-pole – the RCD will disconnect the energized wire only.
:* Double-pole or two-pole – the RCD will disconnect both the energized and return wires.
:* 1+N and 1P+N – non-standard terms used in the context of RCBOs, at times used differently by different manufacturers. Typically these terms may signify that the return (neutral) conductor is an isolating pole only, without a protective element (an unprotected but switched neutral), that the RCBO provides a conducting path and connectors for the return (neutral) conductor but this path remains uninterrupted when a fault occurs (sometimes known as "solid neutral"),<ref>[http://www.voltimum.com.au/content/rcbo-2-pole-and-1pn Explanation on voltimum.com.au, by specialist Ian Richardson].</ref> or that both conductors are disconnected for some faults (such as RCD detected leakage) but only one conductor is disconnected for other faults (such as overload).<ref>http://docs-asia.electrocomponents.com/webdocs/01e3/0900766b801e3b4d.pdf (states that there is "2 pole switching of phase [energized] and neutral [return]", but then only identifies the energized conductor as being protected against "overloads and short circuits").</ref>