AM2 / AM2S cheat sheet

Safe isolation sequence: identify the supply, isolate, lock off, prove dead at the point of work, then re-prove the voltage indicator.

An approved voltage indicator to GS38 has fused leads, finger guards, limited exposed probe tip and must be proved on a proving unit before and after use.

The Electricity at Work Regulations 1989 require dead working where reasonably practicable; live work is permitted only when justified, authorised and risk-assessed.

Hierarchy of control: eliminate the hazard, substitute, apply engineering controls, then administrative controls, with PPE as the last resort.

Risk assessment for electrical work covers shock, arc flash, burns, fire, stored energy and the effect of the environment on the work.

Band II low voltage is above 50 V AC to 1000 V AC, or above 120 V DC to 1500 V DC; safe isolation procedures apply to all live conductors.

A lock-off device and caution notice are fitted at the isolation point, and the key is retained by the person carrying out the work.

A proving unit provides a known voltage source to confirm the indicator operates correctly before and after proving dead.

Cable current-carrying capacity: Iz = It × Ca × Cg × Ci, and Iz must be at least the nominal device rating In and design current Ib.

Flat twin-and-earth cable clipped direct is Reference Method C; current-carrying capacities are selected from BS 7671 Table 4D5.

Main protective bonding conductor minimum is 6 mm² copper, and 10 mm² for a PME supply, per BS 7671 Table 54.8.

For line conductors up to 16 mm² the circuit protective conductor may be the same size; larger line conductors follow BS 7671 Table 54.7.

A ring final circuit uses 2.5 mm² line and neutral with a 1.5 mm² CPC, a 32 A protective device and a floor area not exceeding 100 m².

Conduit fill must not exceed 40 percent and trunking fill must not exceed 45 percent of the internal cross-sectional area.

Socket-outlets intended for use by ordinary persons require 30 mA RCD additional protection under BS 7671 Regulation 411.3.3.

Cable bending radius follows the manufacturer's instruction; non-armoured fixed wiring is commonly not less than 4 times the overall cable diameter.

Band I, Band II and Band III circuits are segregated, and fire alarm and emergency lighting cables require fire-resistant support.

Initial verification sequence: continuity of protective conductors, ring final circuit continuity, insulation resistance, polarity, external earth fault loop impedance, RCD operation, then functional testing.

Insulation resistance is measured at 500 V DC with a minimum acceptable value of 1 MΩ for 230/400 V circuits; SELV and PELV use 250 V DC and 0.5 MΩ.

Ring final circuit continuity uses end-to-end readings r1, rn and r2; with cross-connection the expected R1 + R2 is (r1 + r2) divided by 4.

RCD testing: no trip at half rated residual current, trip within 300 ms at rated current, and trip within 40 ms at five times rated current for a 30 mA device.

External earth fault loop impedance Ze is measured at the origin with main protective bonding disconnected and compared with BS 7671 Table 41.3 or 41.4.

Polarity checks confirm the line conductor is connected to the MCB or fuse, neutral to the neutral bar, and CPC to the earth bar.

An Electrical Installation Certificate is used for new work, a Minor Electrical Installation Works Certificate for minor work, and an Electrical Installation Condition Report for periodic inspection.

Continuity test leads are nulled before use, and supply characteristics and ambient temperature are recorded on the schedule of test results.

Isolation must disconnect all live conductors; switching only the line conductor is not isolation.

Prove dead at the point of work between line and neutral, line and earth, and neutral and earth using an approved two-pole GS38 indicator.

Re-prove the indicator on a proving unit after testing; if the indicator fails to operate, the circuit is treated as live.

Fit a personal padlock and multi-lock hasp at the isolation point, and retain the key until work is complete.

RCDs, emergency stops and control switches are not isolation devices; use the isolator or main switch.

Check for backfeed from PV, generators, UPS systems and borrowed neutrals before proving dead.

A warning notice stating that persons are working must be fixed at the isolation point.

A borrowed neutral is detected by isolating the circuit and checking for voltage on the neutral conductor.

The half-split method divides a circuit into sections and tests each half to locate an open circuit or low insulation fault.

Low insulation resistance is caused by moisture, cable damage, crushed conductors or a faulty connected appliance.

High continuity resistance indicates a loose terminal, corroded conductor or damaged circuit protective conductor.

RCD tripping is investigated by dividing circuits, testing appliance leakage and comparing cumulative leakage with the 30 mA threshold.

High earth fault loop impedance requires verification of Ze, conductor continuity, CPC size and connection quality.

A short circuit produces immediate high current and rapid protective device operation; an overload produces sustained current above the device rating.

Voltage drop is calculated as millivolts per amp per metre × design current × length divided by 1000, then compared with 3 percent for lighting or 5 percent for other circuits.

Prove the test instrument before and after fault-finding, and isolate the circuit before resistance or continuity testing.

Part P applies to domestic electrical installations in England and Wales; notifiable work requires building control notification or a registered competent person.

BS 7671 is not statute law but provides the accepted standard for complying with the Electricity at Work Regulations 1989 and the Health and Safety at Work etc. Act 1974.

Building Regulations relevant to electrical work include Part B for fire, Part M for access, Part L for energy efficiency and Part P for electrical safety.

The Health and Safety at Work etc. Act 1974 imposes duties on employers to ensure the health, safety and welfare of employees and others affected.

CDM 2015 requires coordination of health and safety throughout a construction project, including a construction phase plan where applicable.

30 mA RCD additional protection is required for socket-outlets up to 32 A for ordinary persons and for mobile equipment up to 32 A used outdoors.

Notifiable domestic work includes new circuits, consumer unit replacement and work in special locations; like-for-like accessory replacement is generally not notifiable.

Waste electrical and electronic equipment must be disposed of through a licensed waste carrier and not placed in general waste.