SS638 is Singapore's baseline standard for electrical installations — and it specifies exactly which tests must be performed before you can certify an installation. If you're an LEW signing off a CCC, you need to understand every clause of the testing requirements.
Every Singapore LEW has heard of SS638. Not every Singapore LEW has read it carefully enough to know exactly what tests it mandates, in what order, with what pass/fail thresholds, and with what documentation requirements. This matters because when you sign a Certificate of Completion and Compliance, you are personally declaring that the installation complies with SS638. If it doesn't, and someone is killed or injured, your signature is the paper trail that leads to you.
SS638 compliance testing in Singapore is not complex, but it is specific. This guide goes clause by clause through the verification and testing requirements of SS638 Part 6, tells you exactly which instrument you need for each test, and gives you the threshold values to measure against.
Key Stat
SS638 Part 6 lists 9 mandatory test categories. A typical Singapore LEW completing a CCC for a new commercial fit-out installation must perform all 9 categories of tests, document the results with actual measured values (not just 'pass'), and sign the documentation under personal professional liability.
The first test, and arguably the most fundamental: every circuit's protective conductor (earth wire) must form a continuous path from the circuit's earthing point back to the main earthing terminal (MET). If this path is broken — because a screw terminal wasn't tightened, because a crimp joint was missed, or because a plug-in connector is faulty — earth fault protection will not function.
How to test: Disconnect from the supply. Using a low-resistance ohmmeter or the R1+R2 method with a long test lead, measure the resistance of the protective conductor end-to-end. For final circuits, the resistance of the protective conductor (R2) should be low enough that, combined with the phase conductor resistance (R1), the resulting earth fault loop impedance satisfies the disconnection time requirement.
What you need: A low-resistance continuity tester with a test current of at least 200 mA (to avoid errors from surface oxide on screw terminals). A standard multimeter's continuity mode typically uses very low test current and will pass corroded connections that would fail under fault current. Use a dedicated electrical tester with rated continuity test current.
With all equipment disconnected or isolated, test the insulation resistance between each live conductor and earth, and between live conductors (line-to-neutral). The SS638 minimum requirement is 1 MΩ for LV circuits. In practice, a healthy new installation should read well above 200 MΩ.
Test voltage: 500 V DC for standard 230/400V LV installations. 250 V DC for SELV circuits.
What to disconnect first: All surge protection devices (SPDs), dimmers, electronic ballasts, VFDs, and sensitive electronic equipment must be disconnected before applying 500 V DC. Failing to do so will damage equipment and produce invalid test results.
What you need: A calibrated megohmmeter with stable 500 V DC output. For large installations, a digital insulation tester with memory and PC download capability saves enormous time on documentation. See our insulation tester range for SS638-appropriate instruments.
Watch Out
If you test insulation resistance with all surge protection devices connected — as many electricians do in a hurry — the MOV suppressors inside the SPDs will conduct at 500 V DC and produce a falsely low insulation resistance reading. The reading may show 0.1 MΩ or even lower, making a perfectly good installation look like a failed one. Always disconnect SPDs before IR testing. Note this in your test records so the next inspector understands the test configuration.
Earth fault loop impedance (EFLI or Zs) is probably the most technically demanding SS638 test to get right. It measures the total impedance of the fault current path from the phase conductor through the fault point, through the protective conductor, back to the source transformer. If Zs is too high, a fault won't produce enough current to operate the overcurrent device within the required disconnection time — meaning the circuit stays live long enough to kill someone.
SS638 specifies maximum Zs values for every type and rating of protective device, for two disconnection time requirements: 0.4 seconds (final socket outlet circuits) and 5 seconds (distribution circuits). The calculation is based on the available fault current needing to exceed the device's threshold within the allowed time.
Example for a 16A Type B MCB on a socket outlet circuit: The MCB must operate within 0.4 seconds at 5× its rated current (80A). At 230V, maximum Zs = 230/80 = 2.875 Ω. Your measured Zs must be below this value — typically with a safety margin applied.
What you need: An earth fault loop impedance tester capable of measuring Zs accurately on circuits protected by RCDs (standard loop testers use a test current that trips RCDs — you need a tester with an RCD-safe measurement mode). Browse electrical testers that combine loop impedance and RCD testing.
SS638 requires verification that every RCD trips within the required time at its rated residual current. For 30 mA RCDs protecting socket outlet circuits, the maximum trip time is 300 ms. Type S (selective/delayed) RCDs must also meet their time-delay specification.
The test procedure requires a dedicated RCD tester — not the test button. See our detailed guide on RCD testing for the full procedure. The instruments you need are covered in our electrical tester range.
Key Stat
SS638 Section 6.4.3 specifically requires that RCD tests be performed using a suitable instrument that measures the actual disconnection time. Test button verification alone does not constitute a valid SS638 test result. This is one of the most frequently observed deficiencies in Singapore inspection records reviewed by EMA.
Verify that all single-pole switches and protective devices are in the line (phase) conductor, not the neutral. A switch or MCB in the neutral leaves equipment energised when apparently switched off — a serious electrocution hazard. This test requires a simple voltage tester, but it must be done systematically across every outlet and switch position.
What you need: A voltage indicator or multimeter rated for the installation voltage. For new installations, check polarity with a purpose-designed polarity tester after energisation.
After all the electrical tests, SS638 requires functional testing of all installed equipment: motors run in the correct direction, interlocks operate as designed, emergency stops function, RCDs trip on the test button, alarm systems respond. These tests verify that the installation works as intended, not just that it's electrically sound.
For building services, functional tests may require coordination with the BMS contractor, mechanical engineers, and SCDF for fire alarm integration. Plan this as a separate commissioning phase, not an afterthought on the day of certification.
SS638 Part 6 Section 6.1 requires that instruments used for testing be verified as suitable for the purpose and appropriately accurate. While the standard does not specify calibration intervals, professional practice and EMA expectations require annual calibration from an accredited laboratory.
Our SAC-SINGLAS accredited calibration laboratory provides traceable calibration for all instruments used in SS638 testing — megohmmeters, loop testers, RCD testers, continuity testers, and multimeters. Certificates carry ILAC-MRA endorsement, accepted by EMA, BCA, BMS contractors, and major Singapore property developers as evidence of instrument accuracy.
For a complete SS638 compliance test kit, speak to our technical team via the contact page. We can recommend the minimum viable kit for a sole practitioner LEW through to full multi-function test sets for larger M&E firms conducting high-volume periodic inspections.
What is SS638 and why does it matter for Singapore electricians?
SS638 is the Singapore Standard for Low-Voltage Electrical Installations (equivalent to the international IEC 60364 series). It is the foundational technical standard that CP5 and the Electricity Regulations reference. When an LEW signs a Certificate of Completion and Compliance (CCC) for a new installation or a periodic inspection report, they are legally declaring that the installation meets SS638 requirements.
What tests does SS638 mandate for new electrical installations?
SS638 Part 6 mandates the following tests in order: (1) continuity of protective conductors; (2) insulation resistance testing; (3) protection by SELV/PELV; (4) protection by electrical separation; (5) floor and wall resistance; (6) polarity check; (7) earth fault loop impedance; (8) additional protection verification (RCD testing); and (9) function tests. All tests must be completed and documented before energisation.
What is the maximum earth fault loop impedance allowed by SS638?
The maximum permitted earth fault loop impedance (Zs) depends on the type and rating of the overcurrent protective device protecting the circuit. For a 16A Type B MCB protecting a socket outlet circuit (requiring 0.4 second disconnection time under SS638), the maximum Zs is approximately 2.87 Ω at 230V. For a 32A MCB, the value decreases proportionally. Your earth fault loop impedance tester calculates or displays Zs directly — compare it against the value in the SS638 disconnection time tables.
Can I reuse test results from a previous inspection for SS638 compliance?
No. SS638 requires that tests be performed on the installation as it exists at the time of inspection. Results from a previous inspection are historical records — they don't certify the current condition. Any addition, alteration, or extension since the last inspection requires testing of the affected circuits, and a periodic inspection requires full testing of the entire installation within scope.
Do my test instruments need to be calibrated for SS638 compliance in Singapore?
SS638 does not prescribe calibration intervals, but the Electricity Act and your professional obligations as an LEW require that test results are accurate. EMA has taken action against LEWs who produced test records using instruments of unknown accuracy. Best practice — and the standard expected in any legal dispute — is calibration annually from an accredited laboratory with traceable certificates.
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