ELE/Cable Work/TBT-ELE-016

Electrical Testing and Commissioning Safety

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Electrical testing verifies that installations are safe before being energised and handed over for use.
Tests include continuity, insulation resistance, earth fault loop impedance, and RCD operation checks.
Testing involves applying test voltages to circuits — creating a risk of electric shock during the process.
Only competent electricians holding appropriate qualifications should carry out electrical testing.
Insulation resistance testing applies 500V DC to circuits — live conductors must not be touched.
Earth fault loop impedance testing is performed on energised circuits, requiring additional caution.
Test instruments must be calibrated, in good condition, and appropriate for the circuit being tested.
Proving units must be used with voltage indicators to confirm they are functioning correctly.
Test results are recorded on Electrical Installation Certificates or Minor Works Certificates.
Any faults found during testing must be rectified and retested before the circuit is energised.

Electric shock	Testing involves applying voltages and working on energised circuits, creating direct shock and burn hazards.
Installation safety	Testing is the final safeguard that confirms the installation will not cause shock, fire, or equipment damage.
Legal requirement	BS 7671 requires initial verification testing before any new installation is connected to the supply.

Don't

Ensure only competent qualified electricians carry out electrical testing work
Use calibrated test instruments appropriate for the type and voltage of the circuit
Prove the voltage indicator is working using a proving unit before and after each test
Isolate circuits before carrying out insulation resistance or continuity testing
Wear appropriate PPE including insulated gloves for live testing procedures
Record all test results on the appropriate certificate form as required by BS 7671
Rectify any faults found during testing before energising the circuit for use
Brief other trades that testing is in progress and circuits may be temporarily live
Keep test leads in good condition — damaged leads create shock risk during testing
Verify the test instrument calibration date is current before starting any testing

DON'T allow unqualified persons to carry out electrical testing on any installation
DON'T use test instruments that are out of calibration or visibly damaged
DON'T skip the proving unit check on voltage indicators — false readings kill
DON'T touch exposed conductors during insulation resistance testing at 500V DC
DON'T energise circuits with faults identified during testing — repair and retest first
DON'T perform live testing procedures without appropriate insulated PPE
DON'T test circuits while other workers are connecting or working on them
DON'T issue an Electrical Installation Certificate for installations with unresolved faults
DON'T use test leads with damaged insulation or cracked probes
DON'T rush testing to meet handover deadlines — inaccurate results endanger future users

See also: Electrical Safety Awareness | Isolation and Safe Systems of Work

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