How to Safely Isolate Electrical Equipment on Industrial Sites

Table of Contents

• Why Safe Isolation Matters on Industrial Sites
• Identifying the Circuit, Equipment and Every Energy Source
  • Accounting for multiple feeds and complex equipment
• Obtaining Permission, Risk Assessment and Coordinating the Work
• Electrical Safe Isolation Procedure: Switching Off and Isolating
• Lock Off and Tag Out Procedure
  • Group lockout and lock boxes
  • Shift handover and changing crews
• Prove Dead Procedure: Testing Before You Touch
• Industrial Electrical Isolation Checklist and Restoring Supply
• Booking Your Isolation Procedure Training
• Frequently Asked Questions

Electrical isolation is the process of cutting off every source of electrical energy to a piece of equipment so that you can safely isolate electrical equipment before work begins, without the risk of shock, burns or unexpected start-up.

This guide walks through the full approach, from identifying the equipment to restoring supply safely. It is written for the people who carry this work out and the managers who sign it off. The steps below reflect principles behind HSG47 and GS6 guidance.

Why Safe Isolation Matters on Industrial Sites

To safely isolate electrical equipment, you must treat isolation as the single most important control for preventing electric shock and arc flash injuries on site.

Many accidents happen not because workers ignore the rules, but because they assume a circuit is off.

Good isolation also protects the wider operation. A clear procedure means fewer unplanned shutdowns, fewer near misses and a workforce that trusts the system.

Identifying the Circuit, Equipment and Every Energy Source

Before anything is switched off, the person in charge needs to know exactly what they are isolating. Start with the drawings, single-line diagrams and the equipment’s own nameplate. Confirm the circuit on site, not just on paper, because drawings are often out of date and a panel may have been modified since the last revision.

On industrial plant, the hard part is rarely the main supply. It is the second, third and fourth source that nobody remembered. Work through the following for every item of equipment:

• Identify the equipment by its tag number, location and function, and match it to the drawing before you touch anything
• Trace every supply, including standby generators, UPS units, dual-fed distribution boards and interlocks from other plant
• Find the point of isolation for each supply, a circuit breaker, disconnect switch, isolator or removable link, and confirm it actually isolates the section you are working on
• Check control circuits, which may run at a lower voltage but can still be fed from a separate source and remain live when the power circuit is dead
• Look for backfeeds from motor drives, regenerative loads, parallel panels, neighbouring equipment and temporary supplies
• Note stored energy, such as capacitors, springs, hydraulic pressure, pneumatic pressure or elevated machinery

Accounting for multiple feeds and complex equipment

A single item of equipment can be fed from more than one direction. Common patterns include:

• Dual-fed boards and changeover arrangements, where either of two supplies can energise the same busbar
• Motor drives and inverters, which can feed energy back into the circuit even after the supply is switched off
• UPS and battery systems, which maintain voltage on circuits that appear dead
• Generators and embedded generation, which may run independently of the mains supply
• Interconnected machinery, where one line can back-feed another through shared services or control wiring

The practical approach is to build a source map for the equipment before work begins. List every supply, every isolation point and every stored-energy source on one sheet, then walk the route on site and tick each one off. If you cannot account for a source, stop and investigate, do not assume it is dead.

Multiple feeds are the usual reason isolation goes wrong, so check each one against the sources below.

Obtaining Permission, Risk Assessment and Coordinating the Work

No isolation should start without authority. On most sites, an authorised person issues a permit or safe system of work that sets out the scope, the isolation points and who is responsible at each stage.

Before the permit is issued, carry out a short risk assessment. It should cover:

• The voltage and fault level of the equipment
• Whether any part of the system must stay live, and how that is controlled
• Access, lighting and the working environment
• The people involved and their competence
• What happens if the isolation fails or the work overruns

Coordinate with operations, other trades and the shift team. Tell everyone affected that the equipment will be down, and agree how the work will be handed back. Clear communication stops someone restarting plant while another person is still inside it.

Electrical Safe Isolation Procedure: Switching Off and Isolating

This is the core of the process. Follow the steps in order every time, and never skip one because the job looks simple.

1. Notify everyone affected that isolation is about to begin
2. Switch off the load at its normal control point
3. Open the isolation device at each point of isolation
4. Secure each device so it cannot be closed by accident
5. Prove the circuit is dead using the method described below
6. Apply your personal lock and warning tag

The electrical safe isolation procedure is only complete when every point of supply has been opened, secured and proven. If any single source is missed, the whole isolation is unsafe.

Watch out: Switching off at the control panel is not isolation. A stop button or software command only stops the load.

Lock Off and Tag Out Procedure

Locking off physically prevents anyone from reconnecting the supply while work is underway. Tagging out gives a written warning of why the isolation is in place. On a single-worker job this is straightforward; on an industrial site with multiple trades, contractors and shift changes, the procedure has to be designed to survive people coming and going.

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A proper lock off and tag out procedure normally includes:

• A personal padlock for each person working on the circuit
• A lock-off device (a hasp or multi-lock clamp) where more than one padlock fits a single point
• A warning tag stating who applied it, the reason, the date and the expected duration
• A lock register or lock box so the team can see who holds each lock and why

Group lockout and lock boxes

Where several people work on the same isolation, use a group lockout arrangement rather than a chain of personal locks on the device itself:

1. The authorised person applies the primary lock and tag to the isolation device.
2. A lock box is attached to that primary lock, and the key to the isolation device goes inside the box.
3. Each worker then applies their own personal lock to the lock box and keeps the key.
4. The box cannot be opened, and the isolation cannot be removed, until every personal lock has been taken off.

This gives each worker ownership of the isolation without requiring every padlock to fit the device itself. It also makes it obvious at a glance how many people are protected by the isolation.

Shift handover and changing crews

Isolation ownership must transfer cleanly when a shift ends or a crew changes:

• The outgoing worker removes their personal lock only after the incoming worker has applied theirs and confirmed the isolation is still in place.
• The handover is recorded, who holds which lock, what work remains, and any changes to the isolation.
• The incoming worker re-proves the circuit dead before starting work, even if the isolation appears undisturbed.

Never leave a lock on a device that nobody is actively working under, and never remove another person’s lock. If a worker leaves site without removing their lock, follow the site’s formal lock-removal authority procedure, usually requiring management authorisation, a check that the equipment is clear, and a written record, rather than cutting the lock off informally.

Prove Dead Procedure: Testing Before You Touch

Opening a switch does not prove that a circuit is dead. Faulty equipment, back-feeds and incorrect labelling can all leave a conductor live. The prove dead procedure is the only reliable check.

Use the prove-test-prove method:

1. Prove your voltage tester works on a known live source
2. Test the circuit to confirm it is dead, at every conductor and phase
3. Prove the tester again on a known live source

Use a tester rated for the voltage involved and check its test leads before each use.

Never rely on indicator lamps, panel meters or a colleague’s word. Test at the point of work, and test every phase.

Industrial Electrical Isolation Checklist and Restoring Supply

Before any work is signed off, run through a final check. This industrial electrical isolation checklist is a useful starting point for your site:

• Every energy source is identified on the drawings and on site
• Permit issued and risk assessment completed
• All isolation devices opened and secured
• Circuit proven dead at each phase, with the tester proven before and after
• Personal locks and warning tags fitted
• Stored energy released or controlled
• Everyone affected has been told

Restoring supply needs the same care as isolating it. Confirm that all work is complete and everyone is clear of the equipment. Each person removes their own lock, the permit is closed, and the supply is reconnected in the reverse order. Tell the operations team before any equipment is restarted.

Booking Your Isolation Procedure Training

Written procedures only work when people can apply them under pressure. Practical, hands-on training can help teams understand what to do when they are near live equipment.

SJB Electrical Training offers HSG47 and GS6 training, and AP / Authorised Person and Competent Person courses.

Book your isolation procedure training today, and make safe isolation part of how your team works every day.

Frequently asked questions about electrical isolation are answered in the sections above. For tailored advice on your site, speak to our team.

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