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Metal conduit and SWA as the cpcCan the conduit be the cpc?

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Metal conduit as the cpc

In a lot of metal installations the actual cpc is the metal conduit — and this is something you may well meet in your practical assessment.

How the earth path runs

Metal conduit, earthed at each end of the run
  -> into the metal back box (also earthed)
  -> fly lead from the back box to the front plate
  -> and the cpc of the twin and earth cable back to the MET
You have three legitimate options. Use the metal conduit as the cpc; run a separate cpc inside it; or do both. Both is not required — it is belt and braces — but some people do it.
Either way the conduit gets earthed. It is an exposed conductive part, so it is earthed back to the MET: a fault to it then makes the protective device operate. Terminated with a brass bush or earthing ring and a lock nut.
Types, and a word on names. Black enamel, stainless steel and galvanised steel conduit, alongside PVC. "EMT" is an American term — here it is just metal conduit. And earthing buried conduit matters more because of where it sits: back to your installation reference methods.

SWA, and circuits with no neutral

The armour of steel wire armoured cable can be used as the cpc.

A three-phase circuit may have no neutral at all. With balanced loads you do not need one — the primary side of a transformer carries only the three line conductors, and so can a balanced motor. The neutral comes from the star point on the secondary side.

Using three-core SWA for a single-phase circuit

You sleeve the cores to identify them.

Which colour you use for which does not matter —
what matters is that both ends match.
The conductor that is a neutral at the accessory must land in
the neutral bar at the consumer unit.
The same discipline as two-way switching. The two ends have to marry up. One convention is blue on the grey and green-and-yellow on the black — but it is only a convention. Others may do it differently, and that is fine — as long as both ends match.

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