Electric Shock: Body Current and IEC 60479 AC/DC Zones

The body-impedance calculation follows the framework of IEC 60479-1:2018, edition 1.0. Each percentile has a separate log-domain, shape-preserving cubic representation versus touch voltage. Separate AC dry/wet/saltwater and large/medium/small contact families are retained. Dry large-area DC has its own curve; other DC contacts use the AC estimate described in ETSI TR 102 614 V1.1.1, Annex C, pp.17–18. No standard table or artwork is reproduced.

The hand-to-hand impedance is multiplied by the selected hand-to-feet ratio and sensitivity factor. A bracketed nonlinear root solves body voltage with the external return impedance. Initial resistance R₀ is selected for skin bypass or an entered contact shorter than 10 ms. A verified device configured below 10 ms is evaluated using a separate initial-current candidate: R₀ is applied to the reported exposure only if that candidate actually reaches guaranteed pickup. Otherwise the tabulated model and full contact duration remain in force.

Actual body current is compared with reaction boundary a and muscular boundary b. Only fibrillation uses heart-equivalent current F·I, with F=1 for left hand–feet, 0.8 for right hand–feet and 0.4 for hand–hand. The c₁/c₂/c₃ curves are numerical representations of published graphical positions, interpolated smoothly in log time and current. The upward-DC transition is independently checked at 10, 50, 100, 200 and 500 ms against GOST R 70646.1-2023, Figure A.21. Downward longitudinal DC shifts the continuous-current curves by about two. The national cross-check is not equivalent to IEC 60479-1:2018.

A constant-current exposure is assessed at its actual contact or clearing duration. There is no search over prefix RMS windows. Below 10 ms the short-impulse curve approximation is cⱼ=500j·max[1,(0.004/t)^0.7] mA; the DC continuous-curve extension is joined to its own 10 ms endpoint. Short-impulse VF screening uses the separate, polarity-independent impulse representation from ITU-T K.89 (2012), Figure VI.1.

For a symmetric two-pole IT network, the source is half the pole-to-pole voltage and the earth return is [2(1/Rₚ+jωCₚ)]⁻¹. The displayed steady DC current retains the nonlinear body-impedance solve. A separate linear RC screening circuit uses R_floor=min(R₀·k_z, Z(V_available)·k_body), or R₀·k_z in the explicitly initial-resistance state. Since the tabulated impedance decreases with voltage, this is a lower resistance bound over all attainable body voltages. Its steady leakage cannot fall below the nonlinear steady current; this is checked over voltage and impedance percentiles.

The RC screening circuit has C=2Cₚ, R_th=Rₚ/2, R_load=Rₛ+R_floor and τ=C(R_load∥R_th). Its current is I_tail+(I_peak−I_tail)exp(−t/τ). The declining component is assessed separately using tᵢ=3τ and I_equiv=(I_peak−I_tail)/√6, as published in ITU-T K.89, Appendix VI. Two published capacitor examples independently check this conversion. Applicability requires 0.1 ms≤3τ≤10 ms and contact lasting at least 3τ. The table marks other impulses Unassessed. The impulse VF band and the sustained leakage zone are reported separately; no combined IEC zone is assigned. Charge supplied by capacitor release and insulation leakage balances charge through the RC screening circuit analytically.

The 30 mA AC RCD uses maximum times of 300/150/40 ms at ≥1/≥2/≥5 times rated residual current, with no faster interpolation. No trip is credited below guaranteed pickup, for smooth DC, balanced two-pole contact or an IT first fault.

Dalziel's adult lower-tail benchmarks are currents at which 0.5% lost muscular control (99.5% could release); medians correspond to 50%. DC release differs from AC tetanic let-go. These study values do not define a universal duration-independent release threshold. The elapsed-time control moves only the electrical current indication, opening contact and elapsed marker; it never changes the assessed exposure.

Adult external contact, with the selected contact class at both ends. Asymmetric contact areas are not resolved. External series resistance is linear. AC uses the IEC 50/60 Hz body-impedance magnitude as an effective resistance; the IT return retains its complex impedance. Body phase cannot be recovered from magnitude-only data.

The IT supply is symmetric, with equal insulation resistance and capacitance per pole, initially at ±half the rail voltage to earth. Initial imbalance, converters, active insulation-monitor behavior and other earth paths are excluded. An IT first contact receives no automatic clearing credit.

The RC circuit is a lower-resistance screening model, not a simulation of time-varying skin impedance. Its resistance and steady leakage are bounded; its current waveform is not claimed to be a pointwise upper bound for every possible nonlinear or injured-skin response. The impulse calculation applies the published exponential-discharge equivalence to the decaying RC component. The simultaneous DC offset and impulse are not combined into a biological prediction or a formal IEC zone.

The tabulated contact state approximates measurements around 0.1 s. It does not model progressive skin injury, electroporation or exposure-dependent impedance. The sensitivity input explores a reduced impedance without asserting such a time law.

Screening and education, not permission to touch or a protective-device design criterion. Zones 1–3 do not exclude startle, falls, respiratory impairment, burns or other injury. Zone-4 subdivisions and impulse c bands describe conventional approximate VF regions, not individual probabilities. A c₁ ratio below one is not a safety margin.

Source voltage: 25–1000 V. Medium/small contact curves cover 25–200 V across the body. Below 25 V the endpoint is held, generally overestimating current; this is flagged. Contact duration: 0.1 ms–10 s. Pure 50/60 Hz AC and smooth DC only. AC IT switching transients and uncertain body phase require separate assessment.

The IT impulse-equivalence scope is 0.1–10 ms; a completed 3τ discharge must fit inside the contact. Shorter, longer or prematurely interrupted impulses are explicitly unassessed while steady leakage is assessed separately. Even a supported RC impulse band is a screen of the assumed exponential component. It does not establish a combined IEC zone for the superposed impulse and leakage. The comparison table shows the impulse's equivalent RMS current and 3τ, not its peak current or contact duration.

The full licensed IEC 60479-1:2018 text and IEC TS 60479-2:2017 were unavailable for line-by-line verification. Impedances were cross-checked with open ETSI/NHTSA/ASSP material and GOST R 70646.1-2023, which is explicitly not equivalent to IEC 60479-1. The exact 2018 medium/small tables, graphical positions in the original IEC edition and short rectangular-DC polarity corrections remain unverified against those editions. The rebuilt DC transition uses independently read national published positions, with about 6% graphical reading tolerance in its reference cases. The impulse equivalence is verified against ITU worked examples; the current IEC 60479-2:2019 scope confirms the duration limits and supersedes the 2017 TS.

Graphical fits do not support precision trip settings. Explore at least 15% uncertainty in current; this is not a validated error bound. Check against the standard in force. The 30 mA RCD example follows the cited manufacturer's non-delayed AC envelope, not a current installation-compliance determination. Smooth DC needs compatible detection and DC-rated interruption or a verified system that removes stored energy. Upstream AC interruption can leave the DC bus charged. IT monitoring does not guarantee clearing or harmless capacitive contact.

All RC integrations and equivalence conversions are analytic. The time-curve sample input controls picture resolution only; it no longer controls a clinical window search or a time-stepping solve. Voltage sweeps use 181 solved points by default. Charge balance and resistance/leakage bounds are checked without a transient time grid.