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Cable Sizing Calculator per SS 638:2018 (IEC 60364 / BS 7671) for Singapore

SS 638:2018 (IEC 60364 / BS 7671)2018 EditionSingapore

Cable sizing in Singapore follows SS 638:2018, the Singapore Standard for electrical installations based on both IEC 60364 and BS 7671. Engineers select cables using current-carrying capacity tables, apply tropical ambient derating (35-40 °C), comply with SP Group (utility) connection requirements, and verify voltage drop at 230/400 V, 50 Hz supply.

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Quick Reference Table

Singapore Cable Sizing Key References — SS 638 — SS 638:2018 (IEC 60364 / BS 7671) (2018 Edition)
ParameterValue / RequirementClause Reference
National standardSS 638:2018 — Code of Practice for Electrical InstallationsSS 638:2018, Clause 1
Supply voltage230 V single-phase / 400 V three-phaseSS 638:2018, Clause 132
Frequency50 Hz (SP Group)SS 638:2018, Clause 132
Current-carrying capacityTables derived from IEC 60364-5-52 and BS 7671SS 638:2018, Appendix 4
Design ambient temperature35-40 °C (tropical climate, year-round)SS 638:2018, Table 4B1
Voltage drop limits4% from the origin of the installationSS 638:2018, Clause 525
Utility requirementsSP Group connection standards and metering requirementsSP Group Technical Requirements
Common conductor sizes1.5, 2.5, 4, 6, 10, 16, 25, 35 mm²SS 638:2018, Table 4D1A

How to Calculate Cable Sizing for Singapore

  1. 1

    Determine load per SS 638

    Calculate design current per SS 638 maximum demand rules. For HDB flats, typical connections are 40-63 A single-phase. For condominiums and commercial, use assessed load with diversity per SS 638 Appendix A.

  2. 2

    Select cable type for tropical conditions

    Choose XLPE-insulated cables where possible — the 90 °C rating provides better margin in Singapore's 35-40 °C ambient. PVC cables are used for lighting and smaller circuits.

  3. 3

    Apply tropical ambient derating

    Singapore's year-round 35-40 °C ambient requires derating from the 30 °C reference. At 40 °C, the factor is approximately 0.87 for PVC cables. Apply grouping factors from SS 638 Table 4C1 for circuits in shared trunking.

  4. 4

    Select conductor size

    Choose the minimum conductor size from SS 638 Appendix 4 tables with derated ampacity exceeding the design current. Cross-reference with SP Group minimum requirements for service cables.

  5. 5

    Check voltage drop per SS 638

    Verify total voltage drop from the origin of installation does not exceed 4% per SS 638 Clause 525. At 230 V: maximum 9.2 V. Singapore's compact urban environment helps limit cable run lengths.

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Run compliant SS 638:2018 (IEC 60364 / BS 7671) calculations for singapore — free, instant results with full clause references.

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Frequently Asked Questions

Singapore uses SS 638:2018, a national standard that draws from both IEC 60364 and BS 7671. It is maintained by Enterprise Singapore and is mandatory for all electrical installations in Singapore. Licensed Electrical Workers (LEWs) must size cables per SS 638.
A typical HDB flat uses 2.5 mm² for power circuits (20 A MCB), 1.5 mm² for lighting (10 A MCB), and 4 mm² for aircon circuits. The main incoming cable is typically 16 mm² for a 40 A supply or 25 mm² for 63 A. All sizes per SS 638 Appendix 4.
Singapore's constant 30-35 °C ambient (higher in confined spaces like ceiling voids — 40 °C+) requires derating from SS 638's 30 °C reference. Unlike temperate countries, there is no cold season relief. Cable installations in unventilated ceiling voids and riser shafts need particular attention to derating.

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