Israel Electrician Licensing Exam cheat sheet

Ohm's law: U = I × R; power P = U × I = I²R = U²/R. In AC, use rms values unless stated otherwise.

Three-phase power: P = √3 × U_L × I_L × cosφ for balanced loads; reactive power Q = √3 × U_L × I_L × sinφ.

Series circuit: same current everywhere, resistances add, voltages divide in proportion to resistance.

Parallel circuit: same voltage across branches, conductances add (1/R_total = Σ1/R_i), currents divide inversely with resistance.

Impedance: Z = √(R² + X²); inductive reactance X_L = 2πfL, capacitive reactance X_C = 1/(2πfC).

Power factor cosφ = P/S; correction capacitors reduce reactive current without changing active power.

Kirchhoff's laws: sum of currents at a node is zero; sum of voltages around a closed loop is zero.

RMS and peak: for a sine wave U_rms = U_peak/√2 ≈ 0.707 × U_peak; Israeli low-voltage supply is 230 V phase-to-neutral, 400 V phase-to-phase, 50 Hz.

Design current I_b must satisfy I_b ≤ I_n ≤ I_z, where I_n is the protective device rating and I_z the cable current-carrying capacity.

Voltage drop limit for final circuits in consumer installations is commonly 3% and for the whole installation from origin 5%; verify against SI 100 requirements.

Cable sizing: apply correction factors for ambient temperature, grouping, thermal insulation and installation method to the tabulated capacity.

Diversity/demand factors allow summing expected simultaneous load rather than connected load; document assumptions in the design.

Motor circuits: size for starting current; use I_b based on rated current plus appropriate starting allowance, and coordinate protection with the motor's starting characteristic.

Short-circuit withstand: k²S² ≥ I²t, where k depends on conductor material and insulation, S is conductor cross-section, I and t are fault current and clearing time.

Protective conductor sizing: typically equal to phase conductor up to 16 mm², 16 mm² for 16-35 mm², and half the phase conductor above 35 mm² (subject to adiabatic check).

Neutral conductor may be reduced only where harmonics are low and the load is balanced; for significant triplen harmonics keep full neutral or oversize.

Cable designation encodes conductor material, insulation, sheath and features (e.g., copper XLPE-insulated, PVC-sheathed); read the code before selecting for a location.

MCB types: B trips at 3-5×I_n, C at 5-10×I_n, D at 10-20×I_n; choose type to ride through inrush while clearing faults.

RCD sensitivity: 30 mA for socket circuits and additional protection; 300 mA or selective types for fire protection and upstream selectivity.

RCBO combines overcurrent and residual-current protection in one device; RCCB provides residual current protection only and needs separate overcurrent protection.

Cable installation methods (in conduit in wall, clipped direct, in thermal insulation, buried) each have a distinct current-carrying capacity reference column.

Minimum cross-sections: lighting circuits commonly 1.5 mm², socket circuits 2.5 mm², with larger sizes per load; always confirm against SI 100 tables.

Fuses and MCBs protect against overload and short circuit; they do not replace RCD protection against electric shock.

Cable derating for grouping: multiple circuits in one conduit or trunking require a grouping factor below 1.0 applied to tabulated capacity.

TN-S: separate neutral and protective conductors from the source; TN-C-S: combined PEN split into PE and N at the origin; TT: installation earth electrode independent of the supply neutral.

In TT systems, disconnection relies on RCDs; the earth electrode resistance R_A must satisfy R_A ≤ 50 V / I_Δn.

In TN systems, disconnection time depends on the earth-fault loop impedance Z_s: Z_s ≤ U_0 / I_a, where I_a is the current that trips the device within the required time.

Maximum disconnection times for 230/400 V final circuits are typically 0.4 s (TN) and 0.2 s (TT) for socket circuits up to 32 A; 5 s permitted for distribution circuits per SI 100.

Main equipotential bonding connects metallic water, gas and structural services at the origin with a conductor sized per the incoming supply neutral/phase.

Supplementary bonding ties together exposed and extraneous conductive parts in a location to reduce touch voltage, independent of the main earthing terminal.

Touch voltage limit in normal dry conditions is generally 50 V AC; in wet or special locations lower values and additional protection apply.

Earth electrode resistance can be reduced by deeper rods, multiple rods spaced at least their length apart, or chemical/backfill enhancement.

Five safety rules before work: disconnect, secure against reconnection, verify absence of voltage, earth and short-circuit, and protect adjacent live parts.

Electric shock effects: ventricular fibrillation risk rises sharply above 30 mA; 30 mA RCDs are chosen for additional protection for this reason.

Arc flash: do not approach; de-energize upstream, wear appropriate arc-rated PPE, and treat all conductors as live until verified.

First aid for electric shock: isolate the supply safely, call emergency services, check breathing and pulse, begin CPR if trained, and use an AED if available.

Burns from electric arcs: cool with water, do not remove stuck clothing, and seek medical evaluation even for apparently minor contact.

Live working is permitted only with a written permit, suitable tools, PPE, and a second competent person present; otherwise work de-energized.

Lockout/tagout: each worker applies a personal lock and tag; only the person who applied a lock removes it, following documented procedure.

Step and touch voltage hazards near fallen HV conductors: keep a wide distance and shuffle or hop away rather than stride.

SI 100 is the Israeli National Electrical Code (חוק החשמל and its regulations); it governs installation requirements for low-voltage installations.

SI 900 covers electrical installations in residential buildings and sets requirements for dwelling circuits, socket outlets and protection.

The Electricity Law (חוק החשמל) and the Electricity Regulations (תקנות החשמל) set licensing, inspection and safety obligations for electricians and installations.

Israeli low-voltage supply is 230 V / 400 V, 50 Hz, with a MEN-like combined neutral-earth arrangement at the origin; installations are typically TN-C-S.

Work on installations requires a licensed electrician with the appropriate class (e.g., practical electrician, electrician, electrical engineer) and a Form 1/Form 2 inspection certificate as applicable.

SI 100 requires RCD protection for socket circuits and for circuits in wet locations; verify current amendment because requirements are updated periodically.

Special locations (bathrooms, swimming pools, construction sites, medical) follow dedicated SI 100 sections with stricter zoning and protection rules.

New or modified installations require inspection and testing by an authorized tester before energization, with results recorded on the official inspection form.

Dead tests before energization: continuity of protective conductors, continuity of ring final circuits, insulation resistance, polarity, and earth electrode resistance.

Insulation resistance test: apply typically 500 V DC and require at least 1 MΩ for a healthy low-voltage installation; investigate lower readings.

Earth-fault loop impedance test (live) confirms protective device will disconnect within the required time; compare with Z_s limits.

RCD test: verify trip current and trip time at I_Δn and 5×I_Δn using a calibrated tester; record both values.

Continuity of protective conductors uses a low-resistance ohmmeter; null the test leads before measuring to avoid lead resistance error.

Polarity check ensures line is switched and connected to the correct socket terminal; reversed polarity is a common and dangerous fault.

Fault diagnosis sequence: gather symptoms, isolate, test for voltage, check continuity and insulation, then examine terminations and devices before replacing parts.

Test instruments require valid calibration certificates; record instrument serial numbers and calibration dates on the inspection report.

Transformer EMF equation: E = 4.44 × f × N × Φ_max; turns ratio V1/V2 = N1/N2, and for an ideal transformer V1I1 = V2I2.

Synchronous speed n_s = 120 × f / p (rpm), where p is the number of poles; induction motors run slightly slower at slip s = (n_s − n)/n_s.

Motor torque is proportional to the square of the applied voltage for an induction motor; undervoltage causes overheating and starting failure.

Star-delta starting reduces starting current and torque to one third of direct-on-line values; use only where load torque permits.

Direction of rotation of a three-phase motor is reversed by swapping any two of the three supply phases.

Motor protection: thermal overload relay for sustained overload, short-circuit protection for faults, and phase-failure/undervoltage protection where required.

Transformer losses: copper losses vary with load squared (I²R), iron losses are essentially constant; maximum efficiency occurs when copper losses equal iron losses.

Motor nameplate data (voltage, current, power factor, duty, insulation class, IP rating) must match the supply and environment before installation.