Safe isolation, preparation for inspection and testing, safe working practices
Safe isolation
The procedure
Safe isolation is a sequence, not a single action: identify the circuit and its point of isolation; obtain permission and agree the shutdown with the duty holder; assess the risk; isolate all live conductors at the correct point; secure the device with a lock and warning notice; prove the tester on a proving unit; test the conductors at the point of work; prove the tester again; then begin work.
Use a two-pole voltage indicator to GS38 with fused leads, finger guards and exposed tips no longer than 4 mm. Test line–neutral, line–earth and neutral–earth. Where several people are working, use a multi-lock hasp so the supply cannot be restored until every lock is removed.
Hidden supplies
Look for photovoltaic inverters, generators, UPS and battery systems, dual-tariff or off-peak supplies, emergency lighting, fire alarm supplies, door-entry and PIR feeds, borrowed neutrals, and a second intake at a three-phase board. A single main switch may not isolate everything.
Trap: proving the tester on the circuit you are about to work on. If the indicator is faulty, a live circuit reads dead. Prove on a known source, test, prove again.
Trap: treating the operation of an MCB as isolation, or isolating only the line while the neutral remains connected to a live source.
Rule of thumb: prove – test – prove, on every conductor, at the point of work.
Preparation for inspection and testing
Before you test
Agree the extent, the limitations and the access arrangements with the client in writing - for periodic work this may be the most important document you produce. Collect existing certificates, schedules, drawings and previous reports. Produce a risk assessment and method statement, arrange safe access equipment, barriers, signs and PPE, and agree shutdown times.
Instruments
Every instrument needs a valid calibration certificate (commonly within 12 months), a battery check, and lead checks. Confirm the leads are continuous, correct and within GS38, then null or zero them for low-resistance measurement. The instrument must be of the right type and accuracy: a low-resistance ohmmeter reading to 0.01 Ω, a 500 V insulation tester, a loop impedance tester with a no-trip facility, an RCD tester and an earth electrode tester. Check the measurement category of the tester against the installation.
Order of work
Dead tests first - continuity of protective and bonding conductors, ring continuity, insulation resistance, polarity by resistance - then live tests: external loop impedance, prospective fault current, loop impedance at the extremity, RCD operation and functional checks. Confirm polarity and safe conditions before energising anything.
Trap: a current calibration certificate is not proof the leads are sound - check them.
Trap: starting live tests before dead tests have confirmed the installation is safe to energise.
Rule of thumb: no valid calibration certificate, no certification work.
Safe working practices
The safe system of work
Competence, a risk assessment, an agreed method and the right equipment. PPE: insulated gloves, eye protection, and arc-rated clothing where the fault level justifies it. Insulated hand tools to IEC 60900. Test leads to GS38 - fused, finger guards fitted, probe tips no more than 4 mm exposed, rated to BS EN 61010-031 at the correct measurement category. Leads are easily damaged and should be inspected before every use.
The environment
Working at height, asbestos-containing materials, confined spaces, corrosive or wet environments, dust and heat all change the risk. Consider lone working and emergency arrangements: who raises the alarm, where the first-aid kit and insulated rescue pole are, how the supply is isolated. Protect temporary supplies with RCDs. Keep the client and other trades informed and barriered off from the work area.
Live work
EAWR Reg 10 permits work on or near live conductors only where it is unreasonable for the work to be done dead, where it is reasonable in the circumstances, and where suitable precautions are taken. Convenience is not a justification.
Trap: using a standard multimeter with long exposed probes on a live installation, or removing finger guards to reach a terminal.
Trap: assuming a 30 mA RCD makes live work acceptable.
Rule of thumb: if you would not do it in front of the client and the HSE, do not do it.