SS 638:2018 (Code of Practice for Electrical Installations) is the primary Singapore standard governing the design, installation and testing of all LV electrical installations. Compliance is mandatory under the Electricity Act (Cap. 89A) and enforced by the Energy Market Authority (EMA). All new electrical installations above 45 V must be tested and certified by a Licensed Electrical Worker (LEW) before they can be energised. This guide covers every test required under SS 638, the instruments needed, and how calibration fits into the compliance picture.
What SS 638 covers and who must comply
SS 638:2018 is Singapore's equivalent of the UK's BS 7671, aligned with IEC 60364, covering installations up to 1000 V AC / 1500 V DC, virtually all domestic, commercial and light industrial wiring. Installations above 1 kV are governed separately by SS 555. Under the Electricity (Electrical Installations) Regulations: all installation work must be by or under supervision of an LEW; new installations and major alterations must be inspected and tested before connection; the LEW must complete a Schedule of Inspections and Tests (Form EL1) confirming satisfactory results; and existing installations require periodic re-inspection, typically every 5 years domestic, 3 years commercial, annually for high-risk premises. Non-compliance can expose owners and LEWs to prosecution and void insurance coverage.
Visual inspection: the first step before any instrument test
SS 638 Chapter 6 requires a thorough visual inspection before instrument testing, catching faults instruments cannot: missing earth wires, improperly terminated conductors, unauthorised modifications, unsuitable equipment. Check cable routing and mechanical protection; conductor identification against Singapore's colour code (brown/blue/green-yellow); correct protective device ratings for conductor size; enclosures properly sealed; no visible damage, burning or moisture ingress; correct labelling; and secure earthing/bonding. Defects must be corrected, and the inspection documented, before instrument testing proceeds.
Tests 1 and 2: continuity of protective conductors and ring circuits
Protective conductor continuity confirms every earth wire, CPC and structural bonding conductor is continuous from origin to every point served, a single open circuit or high-resistance joint renders the whole earth protection system ineffective. Tested with a low-resistance ohmmeter at ≥200 mA DC, connected between the main earth terminal and each outlet earth pin or bonded metalwork in turn, against calculated values for conductor length and cross-section. The R1 + R2 measurement (phase plus protective conductor resistance per circuit) is taken with a wander lead at the board, then at each outlet, feeding into the later loop impedance calculation.
Ring final circuits (common in older Singapore commercial buildings) need a specific three-measurement test confirming end-to-end continuity of phase, neutral and earth with no borrowed neutrals or spurious connections, using the same ohmmeter: the resistance at the ring's midpoint should be approximately one quarter of the end-to-end resistance, confirming the ring geometry is intact.
Test 3: insulation resistance
Verifies insulation between live conductors and earth is intact: test voltage 500 V DC for circuits up to 500 V (including 230 V and 400 V TPN systems), minimum acceptable IR 1 MΩ per circuit, all switches closed, lamps removed, equipment disconnected, testing phase-to-earth, neutral-to-earth and phase-to-neutral. Electronic dimmers, RCDs, ballasts and SPDs must be disconnected or bypassed first, SPDs in particular can conduct and be destroyed above their clamping level. See our insulation resistance testing guide for the full procedure, including the Polarisation Index test for motors.
Test 4: polarity
Verifies single-pole protective and switching devices are connected in the phase conductor (not neutral), and outlets/luminaires are correctly polarised, an incorrect reversal leaves a switch that appears off while the equipment stays live. Singapore's colours: Brown = Line, Blue = Neutral, Green/Yellow = Earth (adopted 2009, IEC-harmonised); older installations may still use legacy Red/Black and must be identified during inspection. Verified using the installation tester's continuity or voltage functions, both de-energised and confirmed live during the functional test.
Test 5: earth fault loop impedance
Performed on the energised installation to verify total fault-path impedance is low enough for the protective device to operate within 0.4 seconds for final circuits (SS 638 Chapter 4 ADS requirements). The tester momentarily applies a known load and measures the voltage drop, displaying Zs directly; the LEW compares it against SS 638 Appendix 3 tables for the specific MCB type and rating, or fuse type. This live test most directly confirms shock protection under fault conditions, mandatory for every final circuit, distribution circuit and the supply origin. Multifunction testers from Unitest include an NI (No-Trip) mode for RCD-protected circuits. See our earth continuity testing guide for the underlying principles.
Test 6: RCD testing
RCDs are mandatory for domestic socket circuits, bathroom/outdoor circuits, and portable equipment used outdoors or in wet locations. SS 638 requires functional testing at commissioning: a no-trip test at half rated current (must NOT trip), trip time at rated current IΔN (≤300 ms general, ≤40 ms Type S), trip time at 5×IΔN (≤40 ms), and a push-button mechanical check. Results go on the inspection schedule, and the test also confirms the RCD isn't bypassed. See our RCD testing guide for types (AC, A, B, F) and 30 mA vs 100 mA ratings.
Test 7: functional testing and verification
After instrument tests pass, functional testing confirms the installation performs as intended: switches operate the correct loads, lighting illuminates the correct luminaires, interlocks and protective devices work, catching wiring errors the earlier tests missed.
Equipment required for SS 638 testing
| Instrument | Primary Tests Performed | Key Specification |
|---|---|---|
| Multifunction installation tester | IR, continuity, EFLI, RCD, polarity | 500/1000 V IR; Zs ≤ 0.01 Ω resolution; RCD 10/30/100/300/500 mA |
| Low-resistance ohmmeter | Protective conductor continuity, R1+R2 | ≥ 200 mA test current; 0.01 Ω resolution |
| Approved voltage indicator | Safe isolation, verify dead before work | CAT III or IV rated; two-pole preferred |
| Clamp meter / power analyser | Load current, power factor, harmonics | True-RMS; CAT III rated |
All instruments must be calibrated; for EMA or insurance records, a SAC-SINGLAS accredited lab is strongly recommended. Unitest Instruments' lab (LA-2023-0845-C) calibrates all major testers with certificates traceable to Singapore's NMC, 3–5 working day turnaround.
Record-keeping and certification under EMA requirements
The LEW must issue a Test Report and Inspection Certificate covering the installation description, all test results by circuit, instrument and calibration certificate references, a compliance declaration, and LEW licence and signature. The building owner retains this and a copy goes to SP Group before the connection is energised; EMA may audit records, and falsifying results or signing off without testing is a criminal offence under the Electricity Act with penalties including licence revocation and imprisonment.
Common failures found during SS 638 testing
- Insulation resistance below 1 MΩ: commonly older buildings with wet, overheated or damaged cables. Isolate, trace to the specific section or connection, repair or replace, retest, often at a conduit entry point or water ingress at a junction box.
- Earth fault loop impedance above the tabulated maximum: usually undersized earth conductors, corroded connections, or long runs without adequate protective conductors. Fix by adding supplementary earthing, replacing corroded clamps, or upgrading the protective device.
- RCD fails trip time: aged devices (especially in older HDB flats) may exceed 300 ms; there's no adjustment, replace with the correct type (Type A for modern appliances).
- Polarity reversal: from an incomplete brown/blue changeover during modifications. Trace to the specific socket or junction box and correct; do not re-energise until every outlet is verified.
- Open circuit protective conductor: often an under-tightened screw terminal, leaving equipment unprotected during a fault. Trace, reconnect, and check all terminals in the affected circuit.
Defects must be corrected before the installation is energised or returned to service, with affected circuits retested and the certificate updated. Contact Unitest Instruments at +65 6659 8878 for replacement instruments, calibration, or rental for short commissioning projects.