The safe isolation procedure is the fixed sequence that makes electrical equipment dead and keeps it dead while you work: identify every supply, switch off, lock and tag, deal with stored energy, then prove dead with a tester you have proved first. On a control panel the hard part is not the steps. It is finding every supply. This guide is for learning and revision, for competent persons only: always follow your site rules, your permit system and your employer's written procedure.
What safe isolation means, and what this guide is not
HSE, the UK regulator, says on its electricity FAQ page that live work is never absolutely safe and is justified only where dead working is unreasonable. The default is secure isolation first. It also says you should isolate all energy types, meaning electrical, mechanical, pneumatic, hydraulic and stored energy, lock each isolating device with the key kept by the person working, put warning notices on, and prove dead with suitable test equipment before touching exposed conductors.
This guide describes a safe order of work. It does not train you, authorise you or replace your employer's procedure. Never work live on the strength of a blog post, and do not touch any panel unless you are competent and permitted to.
UK and US terms side by side
The UK and the US teach the same discipline with different words. If you read both, the table below saves confusion.
HSE's practical references are HSG85, a guide to safe working practices for people working on or near electrical equipment and the managers who plan the work, and GS38, HSE guidance on test equipment for low voltage systems. GS38 ties to the Electricity at Work Regulations 1989 and prefers dead working. Read it directly for the rules on test leads and probes; we do not quote its details here.
In the US, OSHA's 1910.147 sets out the energy-control sequence: prepare, shut down, isolate, apply lock and tag, release or monitor stored energy, then verify isolation before work. OSHA's 1910.333 adds that a circuit is not treated as de-energised until it is locked or tagged and then verified by a qualified person with test equipment, and that the check must be able to catch induced or backfed voltage.
Why control panels need extra thought
A house circuit has one supply. A control panel often has several, and the main isolator may switch off only one of them.
| Source in or around a panel | Why it can stay live or hold energy |
|---|---|
| Main incoming supply | The isolator switches this one, but the incomer terminals may stay live |
| Separate control supply | A second feeder or transformer may feed the control circuit |
| 24 V DC power supply | Controls, sensors and PLC I/O can stay live on a battery or UPS |
| External volt-free circuits | Another panel or machine may feed voltage into your terminals |
| Drives and capacitors | A variable speed drive can hold charge after the supply goes off |
| Pneumatic and hydraulic | Air and oil pressure hold mechanical energy in actuators |
| Gravity and springs | Raised loads and sprung parts can move when power is lost |
HSE specifically lists stored energy among the energy types to isolate. For a panel that means reading the drawings first for every incomer, every external supply, every battery or UPS and every drive. Check the manufacturer's warning label on the drive for its discharge time before you open it. If the drawings and the panel disagree, stop and ask.
OSHA also says control-circuit devices such as push buttons or interlocks cannot be the only isolation. Pressing stop is not isolating.
The safe isolation procedure, step by step
The video above is by Martindale Electric, a maker of test equipment, so treat it as a vendor demonstration of the method. It is a short, clear walk through the same sequence.
1. Plan and get permission
Read the drawings and the job instruction. List every supply, every stored energy source and everyone who could be affected. Get permission under your site's permit or authorisation system and tell the people who work nearby.
2. Switch off and isolate
Open the isolating device for each supply you listed. Some panel designs interlock the door with the isolator, so the door cannot open while the supply is on. Do not defeat that interlock.
3. Lock and tag
Fit your own lock to each isolating device, keep the key on you, and attach a warning tag with your name. HSE says to lock each device with the keys kept by the person working. The lock is personal; a shared lock is not isolation for you.
4. Release or contain stored energy
Bleed pneumatic and hydraulic pressure, support raised loads, and wait for drive capacitors to discharge for the time the manufacturer states. Waiting is not a substitute for testing.
5. Prove dead: live-dead-live
Use a two-pole voltage tester and a proving unit, and follow the order below. This is the live-dead-live test.
- Live. Check the tester on the proving unit, or another known source, and see that it reads correctly.
- Dead. Test the isolated circuit. Test between every pair of conductors that matters, phase to phase and phase to earth, at the point of work.
- Live again. Check the tester on the known source again to show it was still working.
NFPA 70E, the US electrical safety standard, describes the same logic in its test-before-touch clause, 120.6 in the editions we know. We only describe it in general terms here because the text we opened was a committee draft, not the published standard: the instrument is verified on a known source before and after, every phase conductor at the point of work is tested, and the test is repeated if conditions change or you leave the site and return. Check the edition your site uses.
6. Only then start work, and keep it safe
If you leave and come back, or something changes, prove dead again. Remove tools and your lock only when the work is finished and tested, and tell everyone before you restore power.
What to record
| Item | Why it matters |
|---|---|
| Supplies and devices isolated | Shows nothing was missed |
| Lock and tag owner | Shows who holds the isolation |
| Tester and proving unit used | Shows the tester was suitable and proved |
| Test results, before and after | Shows the live-dead-live order was followed |
| Time of isolation and of release | Shows how long the equipment was under your control |
Your site will have its own form. The point is that someone else can see what you did and in what order.
Tools, and their limits
Two-pole voltage tester with a proving unit. This is the usual tool for proving dead, because its two probes read between conductors and the proving unit shows it works. HSE's GS38 is the place to read about what makes a test lead and probe suitable.
Multimeter. A multimeter measures well but is a different kind of tool. A high-impedance meter can read ghost voltage, a capacitively coupled signal, on a dead wire. Fluke says it can read up to roughly 80 to 85 per cent of the real voltage. Its LoZ mode, with about a 3 kilohm input, drains ghost voltage and shows near zero on a dead wire while real voltage still reads true. Fluke also says not to use LoZ on sensitive electronics. Whether your site allows a multimeter to prove dead is your site's rule.
Non-contact detector. Fluke describes these as a first check only. They do not prove anything.
Socket testers and RCD buttons. HSE warns that socket testers can mislead, and an RCD does not replace isolation.
For more detail on ghost voltage and on using a meter once the panel is proved dead, see our guide to troubleshooting a control panel with a multimeter.
Practise the order in the lab
EDWartens Lab, our free browser lab, teaches the order in its Panel Lab. At 415 V 50 Hz to IEC practice you lock out with a padlock, hasp and danger tag, prove dead with a two-pole tester and a proving unit using live-dead-live, wire from the schematic, restore power, commission and pass the factory acceptance test. The insulation tester, at 500 V or 1000 V, can only be used on a locked-out, proven-dead panel. It is a simulation: it teaches the sequence and the habit, not the real hazard. See the Panel Lab at lab.edwartens.com or the public pages under /project-sim.
Our free course on electrical safety, arc flash, NFPA 70E and LOTO covers the US side, and electrical fundamentals for technicians builds the basics. For the standards background, read our guides on NFPA 70E training requirements and arc flash PPE categories. Practice sits optionally inside the Free PLC Programming Internship, which is free to join and fully online. It is training, not employment. The optional certificate of completion for any course is a paid add-on and can be verified at edwartens.com/verification; it does not make anyone competent or authorised to work on live equipment.
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Questions
What are the steps of the safe isolation procedure?
Identify every supply and energy source, get permission and warn others, switch off and isolate, lock each isolating device and tag it, release or contain stored energy, then prove dead with a tester you have proved on a known source, and prove it again afterwards. Follow your own site procedure, which governs.
What does prove dead and live-dead-live mean?
Prove dead is the UK term for confirming a circuit has no voltage before work. Live-dead-live is the same idea: check the tester on a known live source, test the isolated circuit, then check the tester on the known source again. Both show the tester worked before and after the reading.
Can a multimeter be used to prove dead?
Some sites forbid it and many prefer a two-pole voltage tester with a proving unit. HSE publishes GS38 as guidance on test equipment for low voltage systems, and it is the document to read for your rules. A high-impedance meter can also show ghost voltage on a dead wire, so a reading needs care.
Are non-contact voltage detectors enough to prove dead?
No. Fluke describes non-contact detectors as a first check only. They help you decide where to look, but they do not replace testing with a proved two-pole tester on every conductor you will touch, and a reading from one is never proof that a circuit is dead.
What is the difference between safe isolation and LOTO?
They cover the same ground under different names. In Great Britain the term is safe isolation, with prove dead. In the US the energy-control rule is lockout/tagout, with verification of isolation before work under OSHA 1910.147 and 1910.333. Both require locks or tags and a test.
Does an RCD count as isolation?
No. HSE states that an RCD does not replace isolation. An RCD trips on certain faults, but it does not make a circuit dead or secure. Only a proper isolating device that you lock off, followed by a proved test, gives a safe condition to work in.
Sources
- HSE: Electricity at work, frequently asked questions (read 16 October 2026)
- HSE: GS38, Electrical test equipment for use on low voltage electrical systems (read 16 October 2026)
- HSE: HSG85, Electricity at work: Safe working practices (read 16 October 2026)
- OSHA: 29 CFR 1910.147, The control of hazardous energy (lockout/tagout) (read 16 October 2026)
- OSHA: 29 CFR 1910.333, Selection and use of work practices (read 16 October 2026)
- Fluke: Dual impedance digital multimeters and ghost voltage (read 16 October 2026)
Written by the EDWartens engineering team for general education. Product names are trademarks of their owners; mentioning them does not imply endorsement. Prices and terms of other providers were checked on the date shown and can change.
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