Zs Calculator (Ze + R1+R2)

Calculate Zs at the furthest point of a circuit from external loop impedance (Ze) and continuity (R1+R2). Compare against BS 7671 Table 41.3 maximum permitted values.

Ze (Ω)

R1 + R2 (Ω)

OCPD (optional, for max Zs)

Rating (A)

Enter Ze and R1+R2 to calculate Zs.

Formula

Zs = Ze + (R1 + R2). Pick a protective device and rating to compare your calculated Zs against the BS 7671 Table 41.3 maximum.

Used in

EICR — recorded per circuit.
Minor works certificate — required before issue.

Reference

BS 7671:2018+A2:2022, Section 411 and Table 41.3

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