11.2 Control Measures

Protection of conductors

Conductors need insulation, enclosure and mechanical protection suitable for the voltage, environment and foreseeable use. Insulation prevents unintended contact or current paths; it does not stop the intended current flowing in the circuit. Cable binding or a conduit is not a repair for damaged conductor insulation.

Common methods of protection include:

• Reinforced plastic spiral binding. Groups cables together so that they do not snag, and gives light mechanical protection.
• Plastic conduit. Lightweight tubing suited to light mechanical protection and chemical resistance.
• Metal conduit. Heavier-duty tubing, usually galvanised to prevent corrosion, giving significant mechanical protection and fire resistance.
• Cable ducts. Ducting also gives mechanical and environmental protection to cables. Ducts can be plastic, metal or concrete and can be large enough to protect many different cables and electrical circuits.

Strength and capability of equipment

The strength and capability of electrical equipment means its ability to withstand the thermal, electromagnetic, electro-chemical or other effects of the electrical currents that can be expected to flow when it is part of a system.

Electrical equipment should be installed in line with the instructions, including the type, size, voltage, current capacity and specific use. The purpose of each device should be confirmed only after it has been reviewed and arrangements made so that it can fulfil that purpose. Even a small device matters. Opening a switch, for example, opens a circuit and stops the flow of electricity. The equipment must withstand weather, chemicals, heat, corrosion and any hazardous environment.

When working with electrical equipment, tools or machinery, workers must also make sure the equipment is properly installed and used correctly. If a power tool needs a 15-ampere outlet, for example, it should be plugged only into a socket that supports that requirement, because a lower-rated socket may overheat or short and injure the worker. Any electrical equipment should also be installed correctly, according to the manufacturer's specifications.

Advantages and limitations of protective systems

The principles, advantages and limitations of the commonly used protective systems follow.

Fuses

A fuse protects an electrical circuit against short circuits and overload. It is a metal wire or thin strip with a low melting point, placed in the circuit as the protective device. Under normal conditions the current in the circuit stays within safe limits. When a fault occurs, such as a short circuit, or a load larger than the circuit can carry is connected, the current rises above the limit, the fuse wire heats up and melts, and the current is broken. The fuse thus protects the machine or equipment from excessive current.

Earthing

Protective earthing connects exposed conductive parts to the protective system so a fault can cause timely automatic disconnection. Its effectiveness depends on the complete installation and protective devices. It is not an instant discharge that makes any fault harmless, and lightning or surge protection involves separate design considerations.

Isolation of supply

Isolation establishes a safe state for work by disconnecting relevant supplies, securing against reconnection and controlling stored energy. Verify that state before work; a normal off switch or tag alone is not sufficient. Restore energy only through the authorised handback procedure. This makes it possible to repair and maintain the system in a safe and secure environment. Lockout and tagout procedures must be followed in any workplace where equipment could release potentially hazardous energy unintentionally if not properly maintained.

Summary notes for Element 11 · Cheat sheet · Glossary. A study aid, not published or endorsed by NEBOSH.