Testing
Pre-test (before energising)
Typical workflow (adapt to the job).
1) Visual inspection +
- Correct accessories/IP ratings, mechanical protection, cable support
- Correct circuit identification and labels
- Tight terminations, no copper showing, CPC present and sleeved
- No signs of damage, overheating, water ingress
- Correct circuit identification and labels
- Tight terminations, no copper showing, CPC present and sleeved
- No signs of damage, overheating, water ingress
2) Dead testing (isolated) +
- Continuity of protective conductors (CPC)
- Continuity of ring final conductors (if applicable) and calculate R1+R2
- Insulation resistance (see section below)
- Polarity checks (where applicable prior to energising)
- Continuity of ring final conductors (if applicable) and calculate R1+R2
- Insulation resistance (see section below)
- Polarity checks (where applicable prior to energising)
3) Record results +
- Write down test results per circuit (R1+R2, IR, etc.)
- Fix issues before energising
- Fix issues before energising
Insulation Resistance (IR) testing
Common gotchas that save time on site.
Before you test
- Disconnect sensitive equipment (LED drivers, dimmers, SPDs, electronic controls, EVSE, etc.)
- Remove lamps if required (some fittings/lamps can skew readings)
- Make sure neutrals aren’t borrowed/shared between circuits (can cause misleading results)
- If you’re getting low readings, split the circuit to find the section causing it
- Remove lamps if required (some fittings/lamps can skew readings)
- Make sure neutrals aren’t borrowed/shared between circuits (can cause misleading results)
- If you’re getting low readings, split the circuit to find the section causing it
Typical minimum values (guidance)
These values depend on your local regulations and the installation type. As a common rule of thumb for LV
circuits, you generally expect IR readings in the megaohms. If you want, I can tailor this table to your
country’s standard.
Quick tables
Useful when estimating R1/R2 and checking device operation.
Copper conductor resistance (approx @ 20°C)
Ω/km (for quick estimates; actual values vary by standard/manufacturer).
| CSA (mm²) | Resistance (Ω/km) | Resistance (mΩ/m) |
|---|---|---|
| 1.0 | 18.10 | 18.10 |
| 1.5 | 12.10 | 12.10 |
| 2.5 | 7.41 | 7.41 |
| 4 | 4.61 | 4.61 |
| 6 | 3.08 | 3.08 |
| 10 | 1.83 | 1.83 |
| 16 | 1.15 | 1.15 |
| 25 | 0.727 | 0.727 |
| 35 | 0.524 | 0.524 |
| 50 | 0.387 | 0.387 |
| 70 | 0.268 | 0.268 |
| 95 | 0.193 | 0.193 |
Reminder: resistance increases with temperature. Use this for rough estimates only.
RCD trip times (quick reference)
Typical maximum disconnection times depend on RCD type and standard. Always verify against your regs and
the device label/test instrument guidance.
| RCD type | Test current | Max trip time (typical) |
|---|---|---|
| General purpose (instantaneous) | 0.5 × IΔn | No trip |
| General purpose (instantaneous) | 1 × IΔn | ≤ 300 ms |
| General purpose (instantaneous) | 2 × IΔn | ≤ 150 ms |
| General purpose (instantaneous) | 5 × IΔn | ≤ 40 ms |
| Time-delayed (S-type) | 1 × IΔn | 130–500 ms (device dependent) |
| Time-delayed (S-type) | 2 × IΔn | 60–200 ms (device dependent) |
| Time-delayed (S-type) | 5 × IΔn | 50–150 ms (device dependent) |
Post-test (after energising)
Typical live checks after power is restored.
Functional checks +
- Verify operation of switches, lights, and controls
- Confirm correct polarity at accessories where applicable
- Verify labeling and circuit identification
- Confirm correct polarity at accessories where applicable
- Verify labeling and circuit identification
Protection device checks +
- RCD/RCBO test button and instrument trip tests (as required)
- Confirm protective device ratings match the circuit design
- Record final results/documentation
- Confirm protective device ratings match the circuit design
- Record final results/documentation