Twin and earth

Twin and earth (often written "T&E" and sometimes "T and E") is a colloquial name in the UK, Australia, New Zealand and other countries for a type of flat sheathed fixed mains electricity cable, containing two insulated current carrying conductors and an Earth connector. In Australia and New Zealand this type of cable is referred to as 'Flat TPS' (Thermo-plastic sheathed), as well as "Twin and Earth" or "Twin with Earth".

These cables comprise two individually insulated current carrying conductors and a Circuit Protective Conductor (CPC = PE = Earth). It is commonly used for fixed wiring in domestic and commercial premises, but it is not intended to be used where it is subject to regular movement or sunlight, because the sheathing is affected by ultraviolet radiation.

In the UK the CPC is uninsulated (bare) and of reduced diameter compared to the main cores. Green and yellow sleeving, which is sold separately, is required to be used to cover the exposed ends.

In the Republic of Ireland the situation is different. IS 201-4:2001 ( I.S. 201 part 4: PVC and Low Smoke Halogen Free Sheathed cables for fixed wiring) permitted both the UK style of twin and earth, and also a version with a CPC with a cross-section equal to that of the main conductors and insulated in green and yellow inside the full length of the cable. However, from 2013, the option for the uninsulated and reduced CPC has been removed from the new standard IS 201-4:2013, and as such is no longer permitted in new Southern Irish installations after a short transitional period.

Mainland UK wiring regulations do not at present (BS7671:AMD3) acknowledge Twin and Earth or Flat TPS with a full sized and insulated (G/Y) earth conductor as a valid cable type, which may be awkward for contractors who work cross-border.

Also available in smaller conductor sizes are versions containing three current-carrying conductors and a circuit protective (earth) conductor. These configurations are commonly used for applications such as switched light circuits, battery-backed emergency lighting which requires a switched and unswitched supply, extractor fans with a run-on timer which require a switched and unswitched supply, mains-powered interlinked smoke alarms, and central heating thermostats.

There is an overall sheath of grey PVC (BS 6004), or white for low smoke compound (BS 7211), although prior to 2005 white PVC was also available.

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