Personnel & earthing safety

This page collects the three checks that concern people rather than equipment. studyOptions.enableTouchProtectionCheck in engines/touch-protection.js computes the earth-fault loop impedance Zs and verifies that the protective device actually operates in time (the required current is back-solved from the same trip-curve library the protection page uses, not from a hard-coded threshold). The study "arcflash" with studyOptions.enableArcFlash1584 in engines/arc-flash-1584.js computes the incident energy, the arc-flash boundary and the PPE category to IEC 1584-2018, from the same fault current and the same clearing time as the other pages. studyOptions.enableGroundGridCalc in engines/ground-grid.js computes the earthing-grid resistance, the ground potential rise, and the touch and step voltages against the GB/T 50065 allowable values.

These three numbers are the ones that decide whether a person survives contact with the installation. The loop impedance decides whether a fault is cleared fast enough to be survivable, which is why it is checked against the disconnection time and why a TT system almost always ends in a residual-current device being required. The incident energy decides the arc-rated clothing and the work permit, so it is a safety-management obligation, not only a design figure. The earth-grid voltages decide whether the earthing design itself is acceptable at the substation. Reviewers treat all three as hard acceptance items and none of them can be replaced by a rule of thumb.

Input: the system earthing arrangement (TN-S, TN-C-S, TT) with the equipment and source earth resistances, the PE conductor section or a manually entered PE path resistance, the fault location, the clearing time, the soil resistivity, the grid area, the conductor length, the mesh spacing and the earth-fault current, plus the equipment type, electrode configuration, gap, working distance and voltage for the arc-flash case → chain: for touch protection the phase-conductor path is taken from the same impedance source as the short circuit and the PE path is added, with resistance and reactance summed separately rather than the magnitudes, giving Zs and then the familiar check that U0/Zs reaches the current required to trip within the disconnection time. For arc flash the bolted fault current is reused from the IEC 60909 study, the intermediate arc current follows the standard equations with the voltage-dependent interpolation, the incident energy follows the standard equation with the enclosure correction, and the boundary and PPE category come out of the same calculation. For the earthing grid the resistance follows the uniform-soil simplified formula, the ground potential rise is the earth-fault current times that resistance, the mesh and step coefficients give the touch and step voltages, and those are compared with the standard allowable values computed from body weight and fault duration → output: the per-loop Zs, check value, required current and status with a suggestion; the arc-flash incident energy, boundary and PPE category; and the grid resistance, GPR, touch and step voltages with a three-state verdict. Linkage: the cable section and length set Zs, so a larger PE conductor and a shorter run improve the disconnection check; the protection settings set the required current and the clearing time, and the clearing time also scales the arc-flash energy directly; the earthing resistance and the earth-fault current set the GPR and therefore the touch and step voltages; and any change in the fault current moves all three checks because they all start from the same short-circuit result. Approximations, all disclosed: when the PE section is not entered it is inferred by the usual rule (PE equals the phase section up to 16 mm², 16 mm² between 16 and 35 mm², and half the phase section above 35 mm²) and a warning is raised; when it cannot be inferred the loop is reported as unknown with null values rather than an invented number; the arc-flash calculation follows the IEC 1584-2018 coefficient tables with the voltage interpolation, and the DC case states explicitly that it is an engineering approximation; the earthing grid uses the uniform-soil simplified formulas with an engineering-estimate fallback when the geometry is incomplete.