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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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1 Common sources of electrical hazards

1.1 Identifying sources of electric shock

Contact with electric potentials is one of the common hazards identified in Section 4.4 in the electrical industry. The risks associated with this hazard are significant. In managing risks associated electrical work, preventing electric shocks is a major part of discharging electrical safety obligations. Potential sources of electric shock include:

• Voltages between phases and between phases and neutral; and
• Voltages between phases, neutral and earth where there is metalwork, damp situations, persons and other conductive surfaces nearby. These conductive surfaces are a source of potential that can cause an electric shock.

Identifying other sources of electric shock can be more difficult, but the following list will help. Sources include:

• Voltages across open switch contacts eg voltage across a light switch on an incandescent lighting circuit or the voltage across a bus tie where one side is de-energised;
• Voltages across undischarged capacitors;
• Voltages on disconnected conductors, particularly neutrals;
• Voltages caused by static electricity, leakage or discharge, or lightning;
• The potential (voltage) between parts of the earth in Multiple Earthed Neutral (MEN) systems can change, sometimes causing electric shocks. The changing earth potential can be due to a number of causes including: a high impedance return path to the low voltage distribution neutral, faults on other parts of the power system or lightning strikes;
• Induced voltages from sources other than the circuit being worked on, eg nearby circuits or radio frequency transmitters;
• Voltages across the secondary terminals of transformers, including current transformers;
• Voltages between parts, or open circuited parts of one earth system, or voltages between different earthing systems;
• Incorrect wiring connections eg transposing active and neutral, commonly referred to as incorrect polarity;
• Faulty equipment, eg the frame of faulty equipment may become energized;
• Voltages from sources near the work being performed. Examples include:
  • Working on a remote area power supply where both AC and DC voltages may be present;
  • Repairing lights on a shop facia when overhead power lines are nearby;
  • Working on transducer circuits when other AC and DC circuits are present; and
  • Working on a power system with multiple circuits that may be of multiple potentials;
• Voltages on the circuit being worked on from other sources including:
  • Illegal connections or reconnections;
  • Uninterruptible Power Supplies (UPS) and backup supplies;
  • Motor generators or alternators;
  • DC on AC circuits;
  • AC on DC circuits;
  • Harmonics eg 3rd harmonic 150 Hz in neutrals and earths where there is a large fluorescent light load; and
  • Back Electro Magnetic Forces (EMF) from collapsing magnetic fields or rotating machinery;
• Step and touch potentials and transferred earth potentials. Transferred earth potentials often result from system faults.

1.2 Tripping of supply on powerlines

If contact is made with powerlines, supply will not be disconnected immediately. In fact, if the fault current is low, the supply may not trip at all.

Depending on the voltage and type of protection, there is an inbuilt delay as long as a number of seconds before disconnection occurs. Even if an overhead feeder does trip, it may reclose and energise the fault again.

1.3 Working near sources of arcing, explosion or fires

Arcs, explosions and electrical faults can cause burns. Workers should be protected from the effects of burns. Examples of triggers for arc, explosions and faults which cause burns include:

• Materials providing a conductive path between sources of potential eg uninsulated tools falling across bus bars;
• Abnormal conditions on circuits such as:
  • Lightning striking mains;
  • Circuits of different voltages touching each other eg HV contacting LV circuits; and
  • High voltage in the secondary circuit of a current transformer if an open circuit occurs when current is flowing in the primary circuit;
• Abnormally high voltages when synchronising different supplies. For example, if the waveforms are 180o out of phase, twice the peak-to-peak voltage may be imposed;
• Voltage multiplication effects such as:
  • Ferro-resonance where the capacitive and inductive components of underground cables and transformers can significantly increase voltages when single-phasing occurs; and
  • Restrike can occur if capacitors are energised, de-energised and re-energised in rapid succession;
• Leakage or electrical discharge causing insulation to be compromised eg a combination of a build up of contaminants on insulators and wet weather or tracking through air voids in pitch filled insulating chambers; and
• Failure of insulating mediums²¹.

The consequences of arcs, explosions and electrical faults are compounded by high fault currents. The potential for injury is extreme because of the rapid release of electrical energy.

The level of electrical energy released can equal 20 times the rated supply current. When high fault currents are present, magnetic forces between the conductors can be high enough to cause the conductor supports to mechanically fail. This causes additional damage.

Protection systems should ensure that these high fault currents only flow briefly. However, when high fault currents are present, circuit protection may not operate to protect a person from electric shock, arcing or explosions.

During the time that it takes to clear the high fault current, the arcs produced have enough energy to cause an explosion, melt metallic switchboard cubicles, cause severe burns and flash burns to the face and eyes, as well as injury from flying debris or dislodged components.

1.4 Working in unsafe atmospheres

After faults and fires, often in emergencies, electrical workers may be exposed to unsafe atmospheres. Toxic gases and lack of oxygen can cause illness and death. General Workplace Health and Safety control measures should be used in these situations.

The method of extinguishing fires should be addressed. Typically, carbon dioxide or powder type devices are used against electrical fires. Extinguishers such as water, foam, and wet chemical should not be used as they significantly increase the risk of electric shock. Further information can be obtained from the Queensland Fire and Rescue Authority website.

1.5 Isolation and access

Hazards identified in section 4.4.1 should be addressed in the context of isolation and access. Hazard sources involving isolation and access include:

• Correctly isolating supply but not discharging residual energy, eg a capacitive charge may be present in power supplies, single-phase motors, or high power factor fluorescent fittings;
• Insulation and equipment failing or partially breaking down;
• Earth connection failing to stop an electric shock in earthed conductive parts when step and touch potentials exist;
• Carrying out the task causes a person, something a person may be holding or something a person is in contact with, to intrude into minimum safe approach distances;
• A power system conducting fault current or being subject to high inrush currents;
• Instructions or markings on the parts being inadequate, incorrect or both;
• Using equipment not designed for or capable of an operation, eg opening a "no load – bus tie" under load conditions or relying on an open circuit breaker as an isolation point;
• Another person energising circuits while a worker is working on them, or a vehicle hitting a pole;
• Natural elements such as lightning or wind causing static charges, overhead mains to clash or a high voltage circuit to fall onto a low voltage circuit;
• The inter-core capacitive effects of long multi-phase cables;
• Changes to wiring not being reflected in drawings, ie the drawings are not "as built". An example: a live control or supervision circuit being present though the drawing indicates otherwise;
• If there has been an error in wiring – opening the isolator may not de-energise the switchboard eg if incorrect connection (incorrect polarity) occurred in the service to an installation, opening the main switch will open circuit the neutral rather than the active;
• Intentionally disabling an interlock to perform a task eg opening the shutter of a "rackable" circuit breaker test to prove de-energised in the orifice;
• Inadvertently disabling an interlock while performing a task, eg in a switchboard with an integrated circuit breaker, isolator and earth switch, the operator accidentally moving the isolator into the earthed position;
• A combination of poor direction and insufficient knowledge, eg a worker is instructed to apply a set of earths and short circuits at a Ring Main Unit (RMU). The worker correctly observes that the isolator is open. However, the worker assumes that the earth switch can be closed because the isolator is open. Most RMUs are configured in such a way that the earth switch earths the cable, not the busbar. In this situation, it is possible that the worker would be earthing and short circuiting a live circuit;
• When applying a set of portable earths and short circuits – accidentally or inadvertently making contact with live parts. If this occurs, the worker is using a device that is conducting fault current;
• The threshold value (lowest level of indication or reading) of a test device causing a misleading interpretation of a test to prove de-energised. Depending on the device used, an indication that parts are not energised, in a high voltage situation, does not mean that low voltage and direct current voltages are absent;
• Application of earthing and short circuiting devices that depend on a conductive path through a fuse or a circuit breaker that is not fit for purpose;
• Ineffective connection to the general mass of the earth, eg the electrode, grid or temporary electrode that the earth from the earths and short circuits relies upon in a situation where a single phase becomes energised;
• Application of the short circuit portion of portable earthing devices prior to the earth tail being connected to the earth;
• Arcing and splattering associated with the application of earths and short circuits causing a hazard. The arcing or splattering may result from using the device in situations that range from energised conductors to residual energy such as capacitance. If the parts are energised, the worker can draw the arc from one phase to the other, causing a phase to phase fault; and
• A potential electric shock path existing once the earth tail is connected to earth. A worker may touch another live part and the earthed connector at the same time. For example, in a Common Multiple Earthed Neutral (CMEN) area, even when working on high voltage, contact between the earthed connector and a low voltage phase can cause an electric shock.

²¹ There are numerous insulating mediums in use that should be considered. Some of the mediums include, polyvinylchloride (PVC), cross linked polyethylene (XLPE), vulcanised insulating rubber (VIR), air, epoxy compounds and resins, zellamite, transformer oil, cable oil, vacuum, sulphur hexaflouride, pitch compounds.

Last updated July 18, 2005

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