Iran Nezam Electrical Supervision Exam cheat sheet

Lighting design uses the lumen method: N = (E × A) / (Φ × CU × LLF), where E is target illuminance in lux, A is area in m², Φ is lumens per luminaire, CU is coefficient of utilization, and LLF is light loss factor.

Illuminance targets (IES/EN 12464-1 practice): offices 500 lux, corridors 100 lux, classrooms 300–500 lux, industrial fine work 750–1000 lux, parking 75 lux.

Receptacle layout rule: no point on a wall may be more than 1.8 m (6 ft) from a general-purpose receptacle along the floor line in dwelling habitable rooms; kitchen countertop receptacles at intervals not exceeding 1.2 m (4 ft).

Small-appliance branch circuits in dwellings: minimum two 20 A circuits for kitchen/dining countertops; laundry a separate 20 A circuit; bathroom receptacles on dedicated 20 A circuits protected by RCD/GFCI.

Continuous loads are taken at 125 % of nameplate for branch-circuit and feeder sizing; the panel busbar and main breaker must exceed the connected demand after factors.

Voltage-drop design targets: ≤3 % on a branch circuit and ≤5 % total from service to load (feeder plus branch); motor starting drop commonly limited to 15 % at the motor terminals.

Box fill and device spacing: a lighting outlet or receptacle outlet must be provided in every habitable room, bathroom, hallway, stairway, garage, and outdoor entrance; switch height typically 1.1–1.2 m above finished floor.

Conductor ampacity tables are corrected by ambient temperature factor and adjusted by conduit fill (bundling) factor; both multipliers apply to the table value before comparing with the breaker.

Standard conduit fill limits (Chapter 9 style): 1 conductor 53 %, 2 conductors 31 %, over 2 conductors 40 % of interior cross-sectional area.

Minimum conductor sizes: 1.5 mm² for lighting circuits, 2.5 mm² for general receptacle circuits, 4 mm² for kitchen/laundry and water-heater circuits (IEC 60364 / Iranian practice); 16 mm² copper minimum for service entrance in many local rules.

Bending radius for insulated conductors: not less than 8× the overall cable diameter for cables ≤ 25 mm, and 10–12× for larger; for conduit, typically 6× the trade diameter.

Colors: phase L1 brown, L2 black, L3 grey, neutral blue, protective earth green-yellow; PEN conductor green-yellow with blue marking at terminations.

Conduit support intervals: rigid metal/PVC conduit every 3 m and within 1 m of boxes; cable tray every 1.5–3 m; flexible conduit max 1 m unsupported at the equipment end.

Derating for more than three current-carrying conductors in a raceway: 80 % at 4–6, 70 % at 7–9, 50 % at 10–20 conductors (IEC 60364-5-52 Table B.52.17 style).

Breaker selection rule: I_breaker ≥ I_design and I_breaker ≤ I_z (corrected cable ampacity); I2 (tripping current) ≤ 1.45 × I_z for overload protection.

Earth-fault loop impedance must satisfy Zs ≤ U0 / Ia, where U0 is nominal line-to-earth voltage (230 V) and Ia is the current that trips the device within the required disconnection time (0.4 s for 230 V final circuits ≤ 32 A).

RCD types: Type AC for sinusoidal AC residual currents, Type A for pulsating DC (electronics, inverters), Type B for smooth DC (EV chargers, PV inverters, some VFDs).

Earthing system designations: TN-S (separate PE throughout), TN-C-S (PEN split at origin), TT (local earth electrode, RCD required), IT (isolated or high-impedance earthed source).

Main equipotential bonding conductor cross-section: ≥ half the largest protective conductor, minimum 6 mm² copper (10 mm² where the supply is larger); supplementary bonding minimum 2.5 mm² (4 mm² if mechanically unprotected).

Earth electrode resistance target: typically ≤ 10 Ω for a single electrode in TT systems; ≤ 5 Ω where specified for sensitive installations; measured by fall-of-potential or clamp method.

Surge protective devices: Type 1 at the service entrance where a lightning protection system exists, Type 2 at distribution boards, coordinated by energy (IEC 61643-11).

The Iranian national building code (مقررات ملی ساختمان) is issued by the Ministry of Roads and Urban Development; Part 13 covers electrical installations and references IEC 60364 as the technical basis.

Part 13 mandates licensed-engineer design and supervision for electrical systems of buildings above the small-installation threshold, with drawings and calculations submitted for approval.

The Iranian electrical installations standard (مبحث ۱۳ and the استانداردهای وزارت نیرو / توانیر distribution regulations) governs service connection, metering, and consumer interface requirements.

IEC 60364 series is the reference for protection, earthing, conductor sizing, and verification; IEC 62305 for lightning protection; IEC 60079 for hazardous-area equipment.

Fire-related requirements reference the national fire code (مقررات ملی ساختمان مبحث ۳) and NFPA 72/101 principles for detection, alarm, and egress lighting.

Standards hierarchy: mandatory national code and utility regulations first, then referenced IEC/EN standards, then manufacturer instructions; conflicts resolve in favor of the mandatory national document.

Verification on completion requires insulation resistance, continuity of protective conductors, earth-electrode resistance, RCD trip test, polarity, and loop-impedance measurement, documented in a test report.

Panel schedule demand: connected load is the sum of nameplate VA; demand load applies demand factors by occupancy (e.g., 100 % for the first 10 kVA of dwelling general load, 40 % thereafter).

Lighting load estimate: 15–25 VA/m² for offices, 10–20 VA/m² for residential, 30–50 VA/m² for retail; use actual luminaire schedule when available.

Three-phase power: P = √3 × U × I × cos φ; per-phase current I = P / (√3 × U × cos φ). Balance single-phase loads across phases to within 10–15 %.

Voltage drop (three-phase): ΔU = √3 × I × L × (R cos φ + X sin φ); single-phase: ΔU = 2 × I × L × (R cos φ + X sin φ), with R in Ω/m at operating temperature.

Copper resistivity at 20 °C is 0.0175 Ω·mm²/m; use 0.0225 Ω·mm²/m at 70 °C conductor temperature for voltage-drop calculations.

Diversity factor reduces the sum of individual maximum demands to the maximum demand of the installation; demand factor applies to a single load group's connected load.

Transformer sizing: kVA = total demand kW / (power factor × loading limit, typically 0.8); allow 20–25 % spare capacity for future growth.

Hazardous-area zone classification: Zone 0/1/2 for gases and vapors (continuous, likely, unlikely), Zone 20/21/22 for dust; equipment must be certified for the zone and gas/dust group.

Protection concepts: Ex d flameproof, Ex e increased safety, Ex i intrinsic safety (ia/ib), Ex p pressurization, Ex n non-sparking; temperature class T1–T6 limits surface temperature (T6 = 85 °C max).

Fire alarm system categories: addressable vs conventional; detector spacing typically 7.5 m (heat), 10.5 m for smoke on flat ceilings with 0.5 m clearance from walls.

Emergency lighting: escape-route illuminance ≥ 1 lux along the centerline, ≥ 5 lux in open areas, 50 % of required illuminance within 5 s and full output within 60 s, 90-minute duration minimum.

Firestop every penetration of a fire-rated wall or floor with a listed system rated to the same fire resistance; cable trays crossing fire compartments require internal and external sealing.

RCD protection is mandatory for socket outlets ≤ 32 A, bathroom circuits, outdoor circuits, and construction-site circuits; 30 mA is the standard personnel-protection sensitivity.

Arc-flash and shock risk assessment: establish approach boundaries, lockout/tagout, and verify absence of voltage before work; PPE level follows incident-energy calculation.

Emergency lighting circuits must be supplied from a source that survives normal supply failure (central battery, self-contained luminaires, or generator), and be independent of normal lighting control.

Fire alarm cabling uses fire-resistant cable (e.g., PH30/PH120 or FPLR/FPLP equivalents) in dedicated conduit, separated from power circuits by at least 300 mm or a barrier.

Elevator (lift) supply: dedicated feeder to the machine room, isolator within sight of the controller, car lighting on a separate circuit, and a two-way communication/alarm supply.

IT and communication cabling: separate pathways from power, minimum 300 mm separation or a grounded metallic divider; bend radius ≥ 4× cable diameter for copper data cable.

Renewable-energy interfaces: PV inverter output requires a dedicated breaker with the inverter's maximum output current × 1.25, a DC isolator at the array, and Type A or B RCD depending on inverter topology.

Generator/ATS installations require a transfer switch that prevents parallel connection with the utility, neutral switching where separately derived, and load prioritization for life-safety loads.

Electric vehicle charging: Mode 3 with a dedicated RCD (Type A + DC detection or Type B), a pilot-control line, and load management where the service capacity is limited.

The licensed engineer (مهندس ناظر) is responsible for conformity of the executed work with the approved drawings, the national building code, and the issued permit; supervision reports are filed at defined construction stages.

The supervision report (گزارش ناظر) must be submitted at foundation, structure, and completion stages; withholding a report halts the occupancy certificate.

Design liability: the designer warrants fitness for purpose of the design; the supervisor warrants conformity of execution; neither may approve a deviation without an official revision.

Contract documents hierarchy: agreement, conditions of contract, specifications, drawings, bill of quantities; the more stringent document prevails for safety and code compliance.

The engineer must declare conflicts of interest and may not supervise work executed by a firm in which they hold a financial interest.

Records to retain: approved drawings, calculations, test reports, material certificates, as-built documents, and correspondence; retention typically spans the project life plus the statutory limitation period.

Non-compliance or negligence can trigger disciplinary action by the construction engineering organization (سازمان نظام مهندسی ساختمان), insurance liability, and civil damages.