The circuit protective conductor (CPC) is used to provide protection from electric shock and to allow sufficient current to flow so the protective devices can trip.  Various national and international standards define the requirements for CPC.  Any CPC is also an important consideration in the calculation of .

Common types of allowable CPC include:

1. a single core cable
2. a conductor in a multicore cable
3. an insulated or bare conductor in a common enclosure with insulated live conductors
4. a fixed or bare insulated conductor
5. the sheath or armouring of a cable
6. a metal conduit, cable management system, or electrical continuous support system
7. an extraneous-conductive-part (subject to regulations)

When considering CPC, myCableEngineering allows the following:

1. cable armour by itself
2. a separate conductor by itself
3. armour combined with a separate conductor

Note: although (3) is quite common, it is not recommended due to the difficulties in evaluating divisions of current between the armour and separate conductor.