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Proving dead: three tests, or tenTen tests on three phase. In what order?

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Proving dead is a fixed set of readings, and doing them in a rhythm is how you stop missing one.

Single phase — three tests, in this order

CPC     — Neutral
CPC     — Line
Line    — Neutral

Three phase — ten tests, in this order

Earth — Neutral   Earth — L1      Earth — L2      Earth — L3   (4)
Neutral — L1    Neutral — L2    Neutral — L3                        (3)
L1 — L2         L1 — L3         L2 — L3                             (3)
                                                                 ----
                                                                  10
Start on your safest conductor and work outwards. Done that way you barely move your hands, you get through it quickly, and you are far less likely to skip a combination. Leave the line-to-line tests until last.
✋At the board is not enough. Go to the point of utilisation as well — the furthest point — and prove it dead there too, because of borrowed neutrals. A neutral taken from another circuit can leave your circuit live at a point while the board reads dead.
Three phase: do not forget the busbar chamber. There may be an open busbar chamber above the board carrying the line conductors. That gets safely isolated too.
"Polyphase" is just an old word for three phase — multiple line conductors. If you meet it in a question it means the same thing.
Single phase — 3 CPC — Neutral CPC — Line Line — Neutral Three phase — 10, in this order from Earth E — N E — L1 E — L2 E — L3 4 from Neutral N — L1 N — L2 N — L3 3 line to line L1 — L2 L1 — L3 L2 — L3 3 Start on your safest conductor and work outwards. Done in that rhythm you barely move your hands — and you are far less likely to skip one.
Ten is not a number to memorise. It falls out of working outwards from earth, then neutral, then between the lines.

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