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• 1. Introduction
• 2. The Electrical Safety Act 2002
• 3. The Electrical Safety Regulation 2002
  • 3.1 Part 2 – Electrical work
  • 3.2 Part 4 - Working around electrical parts
  • 3.3 Part 5 - Electrical installations
  • 3.4 Part 8 - Electrical supply
  • 3.5 Part 12 - Incident notification
  • 3.6 Part 13 - Miscellaneous provisions
  • 3.7 Schedule 2 - Exclusion zones
• 4. Risk management
• 5. Working de-energised
  • 5.1 Scope
  • 5.2 Regulatory requirement
  • 5.3 General
  • 5.4 Low voltage isolation and access
  • 5.5 High voltage isolation and access
• 6. Working live
  • 6.1 Scope
  • 6.2 Regulatory requirement
  • 6.3 Important issues when working live
  • 6.4 What to use to work safely
  • 6.5 Testing and fault-finding
• Appendix A
• Appendix B
  • 1 Common sources of electrical hazards
  • 2 Other electrical hazards to be addressed
  • 3 General elements of a safe system of work

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5.4 Low voltage isolation and access

5.4.1 De-energising and re-energising
5.4.2 Isolating and disconnecting
5.4.3 Proving de-energised
5.4.4 Altering isolation for testing, fault finding and energising

5.4.1 De-energising and re-energising

Switching, de-energising and reenergising must be performed under a safe system of work. Switching includes switching for isolation, return to service, synchronising and so on.

The electrical safety of workers and others should be addressed when switching.

Other electrical safety considerations that should apply to de-energising, the process of de-energising and re-energising connecting parts from all sources, include:

• The capacity of switching devices to make and break load currents, including in-rush currents;
• The capacity of switching devices to make and break fault currents;
• Contingency actions to be taken should a fault occur. Examples include what form of action should be taken if:
  • The main switch is a circuit breaker and the breaker trips the instant it is closed;
  • If a thermal over load trips a motor; and
  • A safety switch (residual current device) trips.
• Connecting sources that may not be synchronised or have the same phase relationship; and
• Creating circulating currents within ring feeds of networks.

5.4.2 Isolating and disconnecting

5.4.2.1 Isolating

Any parts worked on must be isolated¹¹ and proved de-energised unless a safe system of work exists and permission has been granted to work live.

Before you carry out work that is de-energised, you must ensure that supply is effectively isolated.

Matters that should be addressed in the isolation process include:

• De-energising the parts from all sources of electrical potential. To effectively de-energise parts, a number of isolation points¹² may be required;
• Removing hazards from other sources of energy, eg spring tension or hydraulic pressure within mechanisms; and
• Finally, conclusively proving that the parts are de-energised so that electric shock is not possible.

Both electrical and non-electrical workers should clearly understand the method or systems used to isolate and maintain isolation. Isolation points for the job should be explained and, where practical, shown to each of the workers.

A warning or safety sign must be attached in a prominent position on each isolation point or device.

Isolation can be achieved by methods or systems using locks or rendering the mechanism inoperable or a combination of these. In situations where isolation points are able to be accessed by other people, it is important that the isolation method or system is not able to be inadvertently or easily compromised.

Without proper authority, people should not alter, remove or change the status of a tag, lock or the method used to render the mechanism inoperable.

5.4.2.2 Disconnecting

Out of service tags should be used to identify equipment or machinery that is faulty or not suitable for use and has been taken out of service. However, an out-of-service tag does not indicate that equipment or machinery is safe to work on.

Where practicable, the electrical equipment or machinery should be isolated and tagged out of service.

Out of service parts should be left in a safe manner. Since out of service tags apply to electrical as well as non-electrical persons, the safety of all should be addressed.

Where isolation and access is required, the safe system of work should state whether tagging out of service is to occur in addition to isolation and access.

Refer to Section B.2.5 for further information.

For example, tagging on the job of replacing a 45 kW motor on a feedwater pump while maintenance is being performed on the intake ‘foot valve’ would include:

• Circuits for the pump supply, starter control and control and telemetry circuits would be isolated and proved de-energised;
• Out of service tags would be placed in key locations eg on the starter; and
• Personal tags, locks, methods of rendering the mechanism inoperable, or a combination of these would then be installed.

5.4.3 Proving de-energised

Parts must be proved de-energised before work begins. Within the electricity industry, an extensive range of devices can be used to prove parts de-energised. In general, when proving de-energised, a worker should at least know:

• How to determine whether the device is fit for purpose;
• How to determine whether the device is within test, inspection or calibration dates, as applicable;
• How to correctly operate the device, including self test functions, as applicable;
• The technical limitations of the device, tester or equipment used:
  • The threshold value of pick-up for the device eg for series test lamps indication of voltages below 35 volts, can depend on the operator and light conditions
  • Whether the device will detect the presence of DC on AC circuits and vice versa
  • Whether the device indicates induction on a circuit
  • Whether a clean connection is required for accurate readings
  • If the device is to be used outdoors – whether the device is water resistant or waterproof
• The actions required to complete the process of confirming the tester is operating correctly, prove de-energised and re-confirm the tester. These actions should include being able to determine:
  • Is the use of self-test mode preferred to testing the device on a known live source?
  • How can the device be proven if there is no self-test mode and no known source of supply?
  • The sequence of actions required to prove the part de-energised.
• What is deemed a conclusive test, i.e. there is conclusive proof that the part is de-energised; and
• What is deemed an inconclusive test or incorrect test and what action should be taken to resolve the situation.

The method used to prove de-energised must be effective. For example, a panel voltmeter should not be used as the only indication that a part is de-energised.

5.4.3.1 Proving cables de-energised before work

Where work is to be performed on a cable, the cable should be de-energised.

If the cable’s connections are exposed, the connections, attached live parts and so on should be proved to be de-energised and identified before work starts.

5.4.3.2 Cutting cables

Particular attention is drawn to cutting cables. Both ends of the cable should be checked for isolation prior to cutting.

Ensuring that an insulated or covered cable is de-energised can present difficulties. Additional precautions should be taken regardless of whether the cable is low voltage, high voltage or a control cable.

For example, the action of cutting a multi-core control cable is likely to create a hazard if secondary current from a current transformer is present. This hazard may not be initially apparent, ie the cable cutters may not be damaged when the cable is cut. A high voltage may develop across the open circuited secondary winding causing an electric shock, arcing or a fault at a later stage.

Depending on the situation, alternative precautions may include:

• Using a cable spiking or stabbing device that is fit for purpose; or
• A combination of proving de-energised and physically tracing the cable.

5.4.4 Altering isolation for testing, fault finding and energising

At times electrical workers need to alter isolation to be able to test or fault find, or both, on energised parts. Typical examples are the testing performed before returning equipment to service and commissioning new equipment.

Testing, faultfinding or both – and the alteration of isolation points – should be performed in line with a safe system of work. The safe system should address and control exposure to electric shock and electrical explosion.

Matters that should be addressed when isolation points are altered include:

• Ensuring that the isolation system or method is effective and not compromised;
• Eliminating access to the equipment for all persons not directly involved in the work;
• Contingency plans if the test fails or a hazardous situation is discovered; and
• Refer also to section 6.5 of this code for details of hazards associated with testing and fault finding.

¹¹ The term "isolated" is defined in Appendix A.
¹² The term "isolation point" is defined in Appendix A.

Last updated July 16, 2009

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