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Calculators for UK electricians
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Maximum Zs
Maximum permitted earth fault loop impedance for Type B, C and D devices to BS EN 60898 and BS EN 61009-1, with the 80% rule-of-thumb figure for comparing against a measured value.
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Ring final R1+R2
Predict end-to-end r1, rn and r2 and the resulting R1+R2 at a socket before you test, from cable size, ring length and ambient temperature.
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PAT retest interval
Work through a risk-based assessment of environment, equipment class, usage and user group to land on a defensible retest interval.
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These tools are decision aids for competent persons. They do not replace BS 7671, the IET Guidance Notes, or your own judgement on site.
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iPhone · iPad · iOS 18.0 or later · Works fully offline