SPM Pendawaian Domestik cheat sheet

Electrical shock severity depends on current path, magnitude and duration: roughly 1 mA is perception threshold, 10-30 mA causes muscular tetany (cannot let go), 50 mA and above across the heart risks ventricular fibrillation.

Body resistance falls sharply with wet or broken skin; contact voltage above about 50 V AC (extra-low voltage limit under MS IEC 60364) is treated as hazardous in domestic locations.

OSHA hierarchy of control for electrical work: eliminate (de-energise), substitute, engineering controls (insulation, barriers, RCD), administrative controls (permit-to-work, lockout-tagout), then PPE last.

Lockout-tagout sequence: identify all sources, isolate, lock and tag, prove dead with a tester of known good status, then apply earth/ short-circuit where required before work.

Live working is prohibited unless justified as unreasonable to de-energise; requires a written risk assessment, competent authorised person, insulated tools, and a second person standing by.

Arc flash is a short-circuit current through air; incident energy rises with fault current and clearing time, so correct protective device discrimination limits burn injury.

Portable Appliance Testing intervals depend on equipment class and environment: Class I earthed appliances in construction sites need more frequent inspection than Class II double-insulated office equipment.

Emergency response: isolate supply before touching a casualty, call emergency services, begin CPR if breathing is absent; do not apply direct contact to a shock victim still in contact with live conductors.

Ohm's law: V = I x R; power P = V x I = I squared x R = V squared / R. For a 240 V, 10 A load, P = 2400 W and R = 24 ohm.

Series circuit: current common, voltages add, total resistance R = R1 + R2 + ...; parallel circuit: voltage common, currents add, 1/R = 1/R1 + 1/R2 + ...

Single-phase domestic supply in Malaysia is nominally 230 V, 50 Hz (within the 240 V historic tolerance); three-phase line voltage is 400 V with 230 V phase-to-neutral.

Power factor: true power P = V x I x cos phi; reactive power Q = V x I x sin phi; apparent power S = V x I in volt-amperes.

Voltage drop for a single-phase circuit: Vd = (2 x rho x L x I) / A, where rho is resistivity, L length one way, A conductor cross-section; the factor 2 accounts for go and return.

Conductor resistance R = (rho x L) / A; resistivity of copper is about 1.72 x 10 to the minus 8 ohm-metre at 20 degrees C, rising with temperature.

AC reactance: XL = 2 pi f L and XC = 1 / (2 pi f C); impedance Z = square root of (R squared + (XL - XC) squared).

Energy and cost: kWh = power in kW x hours; a 2 kW appliance run 3 hours consumes 6 kWh.

Common domestic cable is PVC-insulated, PVC-sheathed twin and earth (flat) for surface or concealed runs, and PVC single-core in conduit for enclosed wiring; armoured cable is used where mechanical damage is likely.

Conductor colour coding under MS IEC 60446: line brown, neutral blue, protective earth green-yellow; three-phase lines brown, black, grey.

Cable current-carrying capacity must be derated by correction factors: ambient temperature (Ca), grouping (Cg), thermal insulation (Ci) and protective device type, so Iz >= In >= Ib.

Minimum buried conduit depth and separation from gas and water services must be observed; cables in walls require safe zones (horizontal within 150 mm of ceiling, vertical above accessories) or earthed metallic covering.

Jointing must be inside accessible enclosures; no joints in conduit runs or buried without an accessible box, and no twisted-and-taped connections.

Accessories: switches are rated by current and pole configuration (one-way, two-way, intermediate); socket outlets in Malaysia follow the Type G 13 A rectangular-pin standard with a built-in switch.

Cable bending radius should be at least 6 to 8 times the overall cable diameter for fixed PVC cables to avoid insulation stress.

Segregation: extra-low-voltage and communication cables must be kept separate from low-voltage power cables to limit interference and fault transfer.

Overcurrent protection must satisfy Ib <= In <= Iz and the disconnection time requirement; MCBs give overload and short-circuit protection, fuses give both but need correct discrimination.

Earth fault protection: an RCD rated 30 mA is required for socket outlets and locations with increased shock risk; tripping time at rated residual current is not more than 300 ms for general, 40 ms for 30 mA supplementary protection.

Earthing systems: TN-S has separate PE throughout; TN-C-S (PME) combines neutral and earth in the supply and splits at the origin; TT relies on a local earth electrode with RCD protection.

Earth electrode resistance for a TT system should be low enough that the RCD operates within the required disconnection time; typical target is below 100 ohm with a 30 mA RCD.

Main protective bonding connects extraneous-conductive-parts (water, gas, structural steel) to the main earthing terminal; main bonding conductor minimum 10 mm squared copper for typical domestic supplies.

Consumer unit layout: main switch, then RCD/RCBO groups, with circuits arranged so a single fault does not disconnect all lighting; each final circuit has its own protective device.

Discrimination: the upstream device must not trip before the downstream device for a fault in the downstream circuit; achieved by current rating ratio and time-current characteristics.

Protective device breaking capacity must exceed the prospective short-circuit current at its installation point; a domestic consumer unit typically requires 6 kA or higher.

Lighting circuits are commonly wired as loop-in (loop at ceiling rose), joint-box, or conduit systems; the loop-in method keeps each luminaire supplied from a ceiling rose with switched-live, neutral and earth.

Two-way switching uses two two-way switches with strappers; intermediate switching adds an intermediate switch in the strapper path for three or more control points.

Socket outlet circuits: a 13 A ring final or radial circuit; in Malaysia, radial circuits with 2.5 mm squared copper on a 20 A MCB are common, with 30 mA RCD protection.

Maximum demand estimation: sum connected loads with diversity applied; domestic diversity commonly allows lighting at 66 percent of total and socket outlets at 100 percent of the largest plus 40 percent of the rest.

Final circuit design steps: (1) determine load current Ib, (2) select protective device In, (3) select cable size so Iz after derating is at least In, (4) check voltage drop, (5) check disconnection time and earthing.

Voltage drop limits for domestic final circuits under MS IEC 60364 are typically 3 percent for lighting and 5 percent for other circuits from the origin of the installation.

Socket outlet height and location: at least 150 mm above floor level in wet areas and away from cookers, sinks and showers; bathroom sockets require 30 mA RCD and zone restrictions.

Spur outlets: a non-fused spur may supply one socket or one fixed appliance from a ring final; a fused connection unit is used where the load exceeds the spur rating.

Dead tests before energising: continuity of protective conductors, continuity of ring final circuit conductors, insulation resistance (at least 1 Mohm at 500 V DC for a 230/400 V installation), polarity and earth electrode resistance.

Live tests after energising: earth fault loop impedance (Zs), prospective short-circuit current (PSC), RCD trip time and trip current, and functional testing of switches and accessories.

Earth fault loop impedance Zs must satisfy the disconnection time; for a 32 A Type B MCB at 0.4 s the maximum Zs is about 1.44 ohm, for a 6 A Type B about 7.67 ohm (BS 7671 values, 230 V).

Insulation resistance testing requires all loads disconnected and electronic devices removed to avoid damage; test between live conductors and between live conductors and earth.

RCD testing: test at half rated residual current (should not trip), at rated current (should trip within 300 ms), and at five times rated current (should trip within 40 ms).

Polarity test confirms line is connected to the centre pin of the lamp holder and to the switch, not the neutral; reversed polarity is a common and dangerous fault.

Fault finding sequence: verify symptoms, isolate, inspect visually, test systematically from supply to load, then repair and retest; record results on the schedule of test results.

Continuity of ring final circuits uses the r1, rn, r2 method: end-to-end resistance readings and cross-connected readings should satisfy the relationship r1 + rn approximately equal to r2 at each socket.

The Electricity Supply Act 1990 and Electricity Regulations 1994 govern electrical installation work in Malaysia; the Energy Commission (Suruhanjaya Tenaga) is the regulator.

MS IEC 60364 (Low-voltage electrical installations) is the primary Malaysian standard for domestic installations, aligned with IEC 60364.

Work must be carried out by a competent person holding a valid certificate of competency issued by the Energy Commission; installation and testing require appropriate registration.

MS IEC 60445 and MS IEC 60446 cover identification of conductors by colour and alphanumeric marking; green-yellow is reserved exclusively for protective conductors.

The Electricity Regulations 1994 require periodic inspection and testing of installations; domestic installations typically require inspection at intervals specified by the Commission.

MS IEC 61009 covers RCBOs; MS IEC 60898 covers MCBs for household and similar installations; devices must carry the relevant certification mark.

Earthing and bonding requirements follow MS IEC 60364-5-54: main earthing terminal, protective conductors, and main protective bonding of extraneous-conductive-parts.

Certification of completion and the schedule of test results must be issued on completion of new work or alteration, and retained by the installation owner.

A block diagram shows functional units and signal or supply flow without detailing every conductor; a schematic shows electrical connections using standard symbols independent of physical layout.

A wiring diagram shows the physical routing and terminal connections of conductors, including colour coding, used for installation and fault finding.

Standard symbols: circle with cross for a lamp, switch symbol with pole count, MCB rectangle with rating, socket outlet semicircle with pins, earth symbol of three decreasing horizontal lines.

A site plan or layout drawing shows the physical position of accessories, consumer unit, and cable routes with dimensions and scale.

The schedule of test results records circuit number, protective device rating and type, cable size, insulation resistance, Zs, PSC, RCD trip time, and polarity.

As-built drawings must reflect the installation as completed, including any variations from the original design, and are handed to the client with the completion certificate.

Circuit charts fixed at the consumer unit identify each protective device, the circuit it protects, and its rating; they must be updated whenever circuits are altered.

Drawing conventions: line thickness distinguishes power from control or communication, hatching indicates concealed conduit, and a legend explains all symbols used.