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Why bond? Touch voltage and 1667 ΩWhat does bonding actually protect you from?
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Current through a body
Body resistance ≈ 1000 Ω (less when wet) I = V ÷ R = 230 ÷ 1000 = 0.23 A = 230 mA About 50 mA (0.05 A) can stop your heart (cardiac arrest). 230 mA is far more. → it's the CURRENT that kills.
Where 50 V touch voltage comes from
Table 41.5: Zs × IΔn ≤ 50 V so with a 30 mA RCD, Zs up to 1667 Ω V = I × R = 0.03 × 1667 = 50.01 V The same 50 V ÷ IΔn figure (Reg 415.2.2) is used to check that bonding is effective.
A 30 mA RCD is set below the ~50 mA that can cause cardiac arrest. It gives additional protection by cutting off before serious harm.
BS 7671 · Table 41.5: max earth fault loop impedance for RCDs (30 mA → 1667 Ω) · p.77
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