Plug top

Plug top

Socket

Junction box

Plug

One way switch

Practical No9

Ze = the external part of the earth fault loop — from the supply (like the transformer) up to your consumer unit (fuse board).

R1 = the resistance of the line conductor (live wire).

R2 = the resistance of the circuit protective conductor (earth wire).

When you add them all together, you get Zs, which is the total earth fault loop impedance — the complete path electricity would take if there was a fault to earth (like if a live wire touched metalwork).

Zs shows how easy or hard it is for fault current to flow back to the source — the total resistance of the whole fault loop.