TP EIMSA cheat sheet

Touch voltage limits under IEC 60364-4-41: 50 V AC / 120 V DC for ordinary locations; 25 V AC / 60 V DC for wet or confined conductive locations.

Protection by automatic disconnection uses Zs ≤ U0/Ia, where Ia is the current that trips the protective device within the specified time (0.4 s for TN final circuits ≤32 A, 5 s for distribution circuits).

Earth-fault loop impedance measured value must satisfy Zs ≤ 0.8 × U0/Ia when conductor temperature correction is applied to the tabulated value.

IP code: first digit = solids (0–6), second = water (0–9K). IP2X finger-safe, IP44 splash-proof, IP65 dust-tight and jet-proof.

Arc flash boundary and incident energy depend on bolted fault current, clearing time, working distance, and electrode configuration; PPE category follows the calculated incident energy.

Residual current devices: 30 mA for additional (supplementary) protection of socket-outlets ≤32 A; 300 mA for fire protection; type A for pulsating DC, type B for smooth DC.

Live working requires rated insulating gloves, tools and mats per IEC 60900/61111, with retest intervals typically 6 months for gloves in service.

Step and touch potential near substations are limited by earthing grid design; permissible body current follows IEEE 80 (50 kg: 0.116/√t A; 70 kg: 0.157/√t A).

Ohm's law V = I·R; power P = V·I = I²R = V²/R. Three-phase: P = √3·VL·IL·cosφ; reactive Q = √3·VL·IL·sinφ; apparent S = √3·VL·IL.

Impedance Z = √(R² + X²); series resonance at f = 1/(2π√(LC)); power factor correction capacitance per phase C = P(tanφ1 − tanφ2)/(2πf·V²).

Delta: line current = √3 × phase current, line voltage = phase voltage. Star: line voltage = √3 × phase voltage, line current = phase current.

Transformer ratio a = N1/N2 = V1/V2; referred impedance Z2' = Z2·a². Per-unit method: Zpu = Zactual/Zbase, Zbase = Vbase²/Sbase.

Voltage drop (three-phase) ≈ √3·I·L·(R·cosφ + X·sinφ); mV/A/m tabulated values assume conductor at operating temperature.

Symmetrical components: positive, negative and zero sequence; zero-sequence currents flow only where a return path exists (e.g. neutral, earth).

Cable current-carrying capacity depends on installation method, ambient temperature, grouping, soil thermal resistivity and depth; correction factors multiply.

Induced EMF e = −N·dΦ/dt; motor synchronous speed ns = 120f/p; slip s = (ns − nr)/ns.

Conductor colour identification (IEC 60446): brown = line, blue = neutral, green-yellow = protective conductor; three-phase lines brown, black, grey.

Cable designation example N2XH: copper conductor, XLPE insulation, halogen-free sheath; H07V-K is a single-core flexible PVC cable rated 450/750 V.

Minimum cross-sectional area: 1.5 mm² for lighting circuits, 2.5 mm² for socket-outlet circuits (copper), 16 mm² for earthing conductors of larger supplies.

Cable tray fill should not exceed 40–50% of cross-section; conduit fill per IEC 61386 typically 40% for three or more conductors.

Bending radius: fixed cables typically 12 × overall diameter for armoured, 8–15 × for unarmoured depending on standard; never below manufacturer data.

Fire-rated cable (e.g. FE180, PH120) maintains circuit integrity for 30–120 minutes; required for fire alarm, emergency lighting and smoke control supplies.

Cable glands and terminations must match cable type: SWA requires armour earthing gland; Ex installations require certified Ex e or Ex d glands.

Segregation: power and data cables separated by at least 300 mm or a metallic barrier; SELV/PELV kept separate from LV unless insulation rated for highest voltage.

Initial verification sequence (IEC 60364-6): visual inspection, continuity, insulation resistance, polarity, earth electrode resistance, loop impedance, RCD trip test, functional tests.

RCD test: verify trip at IΔn (≤300 ms) and at 5×IΔn (≤40 ms) for general type; verify no trip at 0.5×IΔn.

Insulation resistance test: disconnect electronics, link conductors, apply test voltage for 1 minute, record value at 1 minute; IR ≥ 1 MΩ per circuit.

Earth electrode resistance measured by fall-of-potential (three-pole) or clamp method; target typically ≤10 Ω for a single rod, lower for combined systems.

Loop impedance testers must be calibrated; measured Zs compared with tabulated maximum Zs after applying 0.8 correction for conductor temperature.

Commissioning documentation: test certificates, schedules of test results, as-built drawings, protection settings record, punch list and handover pack.

Protection relay testing: secondary injection for overcurrent, earth fault, differential; verify trip time against coordination study curves.

Phase rotation and motor direction verified before coupling load; check no-load current balance within 10% between phases.

Half-split method: divide circuit or signal path in half, test, repeat - reduces number of test points logarithmically for long circuits.

Nuisance RCD tripping: isolate by disconnecting loads and circuits progressively; distinguish insulation faults (IR test) from cumulative leakage and from transient surges.

Overheating at terminals is caused by loose connection, undersized conductor, high ambient or harmonic current; verify with clamp meter and thermal camera.

Motor fails to start: check supply voltage and phase balance, control circuit, overload relay, winding resistance and insulation, mechanical load.

Intermittent faults: log environmental conditions (temperature, vibration, moisture), use event recorders and trend data; check connectors and cable flex points.

Short-circuit vs earth fault: insulation resistance to earth low indicates earth fault; low resistance between phases indicates phase-to-phase short.

Harmonic problems: check neutral current exceeding phase current, overheating of transformers and neutral conductors; use power quality analyser to record THD.

Safe fault-finding: never assume dead; use approved testers, prove tester on known live source before and after test.

IEC 60364 series covers LV installations; IEC 61936 covers HV installations; national adoptions (e.g. HD 60364, BS 7671, NF C 15-100) apply with local deviations.

IEC 60364-4-41 protection measures: automatic disconnection, double/reinforced insulation (Class II), SELV/PELV, electrical separation, extra-low voltage.

Equipment must be CE/UKCA marked and compliant with applicable directives (LVD 2014/35/EU, EMC 2014/30/EU, ATEX 2014/34/EU); declaration of conformity retained.

Periodic inspection intervals depend on installation type and national rules; records and certificates must be retained and made available to the authority.

Permit-to-work, isolation and live-working procedures are legal requirements under occupational safety regulations (e.g. EU OSH framework directive 89/391/EEC).

Ex area classification (IEC 60079-10-1): zones 0/1/2 for gas, 20/21/22 for dust; equipment group and temperature class must match the zone.

Earthing and bonding requirements: main equipotential bonding conductor ≥ half the supply neutral and ≥6 mm² copper; supplementary bonding sized per local code.

Change control: any modification to a compliant installation requires re-verification and updated documentation before re-energisation.

Test certificate contents: installation identification, extent and limitations, test instruments with calibration dates, results, departures and signature of competent person.

Schedule of test results lists each circuit: conductor sizes, protective device rating and type, Zs, R1+R2, insulation resistance, RCD trip time.

As-built drawings must reflect actual installation, including cable routes, panel layouts, single-line diagrams and protection settings.

Non-conformance report: describe observation, reference the clause, state risk and required corrective action, assign owner and due date.

Calibration records for test instruments should be traceable to national standards; record instrument serial number on every certificate.

Handover pack: O&M manuals, warranties, spares list, training records, emergency procedures and contact list.

Incident reports document time, location, personnel, energy source, injury or damage, root cause and corrective actions; retained per legal retention periods.

Version control on drawings and procedures: unique document number, revision, date, author and approver; superseded copies withdrawn from use.