Testing Your Work

After completing any electrical work, you should test the installation to verify it is safe before energising it. This is required by BS 7671 and is good practice even for simple jobs.

What to Test

Visual checkContinuityInsulation resist.Polarity

Visual Inspection

Before any testing with instruments:

  • All connections are mechanically sound (no loose screws, no bare conductors outside terminals)
  • All earth conductors are connected and properly sleeved green/yellow
  • No insulation damage from staples or drilling
  • Correct cables used (size matches circuit)

Continuity Test

Use a continuity tester or multi-meter to verify:

  • Ring final: end-to-end resistance of L, N, and E conductors
  • Earth continuity: from CPC at socket/light back to consumer unit

Polarity Check

Verify that at each outlet:

  • L terminal is connected to L conductor (brown/red)
  • N terminal is connected to N conductor (blue/black)
  • Reversed polarity is dangerous — fuses blow but equipment stays live when switched off

Insulation Resistance

More advanced — requires an insulation resistance tester (megger). Tests for leakage between conductors and between conductors and earth.

  • Test voltage: 500V DC — always disconnect dimmers, thermostats, and any other electronic components first, as the test voltage will damage them
  • Minimum passing value: 1MΩ (one megaohm) between conductors and earth
  • Disconnect all loads before testing

After Testing

If all tests pass, re-energise the circuit, test each outlet for correct voltage, and verify the protective devices operate correctly.

Certification

Completed electrical work must be properly documented:

  • Minor Works Certificate (MWC): For additions or alterations to an existing circuit (e.g. adding a socket or light point)
  • Electrical Installation Certificate (EIC): For new circuits, new consumer units, or complete rewires

These documents can only be issued by a qualified competent person. For notifiable work under Part P, the certification is also used to notify the local authority. Always obtain and keep the appropriate certificate — it will be required when you sell the property.