What electrical safety ratings mean

For electrical workplace safety in Australia and New Zealand, the safe design of electrical installations and testing requires compliance with local standard AS/NZ 3000, known as the Wiring Rules. Although this standard does not incorporate the International Electrotechnical Commission (IEC) standards for the safety requirements for electrical equipment for measurement (defined in section IEC 61010), it is the care of duty of the electrical works supervisor to ensure the safety requirements for electrical equipment used on the site for electrical measurement meets the IEC 61010 standards.

The preferred way to work on hazardous electrical circuits is with the power off. Equipment that could be turned on must be locked out and tagged. But some tests, such as the current tests that clamp meters perform, simply aren’t possible unless circuits are live.

As the electrical work environment becomes more hazardous, the need for arc-flash, electrical-transient and electrical-shock protection increases. In Australia and New Zealand, there is currently no arc-safety standard and the two major world standards - National Fire Protection Agency (NFPA) used in the US and IEC used in Europe - are the most common being adopted here.

For situations when a location-specific arc-flash hazard analysis is not available, NFPA 70E defines the arc-flash protection boundary for equipment with voltage levels between 50 and 600 b V at 4 feet (1.2 m). (See NFPA 70E section 130.3 (A) (1) for full details.) The standard names a wide variety of electrical maintenance tasks and assigns each a hazard/risk category of 0 to 4. The standard also details the kind of personal protective equipment (PPE) that must be worn when working in the various hazard/risk categories.

The NFPA standard categorises test equipment as PPE and requires that test equipment be rated and designed for the circuits and environments where it will be used. To clarify what this means, the 2009 Edition of NFPA 70E cites American National Standards Institute (ANSI)/ISA- 61010-1 (82.02.01)/UL 61010-1, the standard first established as IEC 61010.

These measurement categories (CAT) listed in the standards cover systems of 1000 V or less, including 415 V and 600 V three-phase circuits. They define the danger of transient voltage spikes and electrical arc-flash and differentiate the severity by location, voltage level and potential for harm.

ANSI, the Canadian Standards Association (CSA) and IEC define four measurement categories:

• CAT IV - Applicable to test and measuring circuits connected at the source of the building’s low-voltage MAINS installation;
• CAT III - Applicable to test and measuring circuits connected to the distribution part of the building’s low-voltage MAINS installation;
• CAT II - Applicable to test and measuring circuits connected directly to utilisation points (power points and similar points) of the low-voltage MAINS installation; and
• CAT I - Defines non-CAT rated products that are not intended to be directly connected to the MAINS supply.

Some installed equipment may include multiple categories. A motor-drive panel, for example, may be CAT III on the 415 V power side and CAT I on the control side.

A higher CAT number refers to an electrical environment with higher power available and the potential for higher-energy transients. A test tool designed to a CAT III standard can resist higher energy transients than one designed to CAT II standards. Within a category, a higher voltage rating denotes a higher transient withstand rating. For instance, a CAT III-1000 V test tool has superior protection compared to a CAT III-600 V rated tool.

By Henk van Velze, Fluke Australia