The CMC 500: The New Benchmark for Personal Safety

Dangers posed by the environment

• Visibility & access: Test locations are often not directly visible. This increases the risk that someone may enter the danger zone without being noticed, or that emergency situations are not detected early enough.
• System errors: When a complete system is being tested, defective components may produce unpredictable reactions – for example, a malfunctioning protection relay may output incorrect signals.
• External influences: Frequently, a number of people may be working in the same work area. In such cases, poor communications or accidental activation can be a source of danger.
   

Dangers posed by the test set or the testing procedure

• Electrical shock: Test sets generate high voltages. Before starting work, the test set (or its outputs) must be disconnected from the power system. Safety plugs should also be used and connected in the correct sequence.
• Wiring errors: Using a large number of cables makes it difficult to keep an overview. Errors can result in damage or personal injuries, so careful and accurate working is essential.
• Incorrect grounding: A broken protective ground wire represents a hazard for people and devices. An additional protective ground is mandatory.
• Procedural errors: Time pressures can tempt people to take short cuts, e.g., carrying out rewiring without switching off the device first.
• Measuring errors: Calibration can become inaccurate as a result of aging or environmental factors. Regular checks must be carried out.

The safety measures that have been adopted in the field are often derived from standards and subsequently enhanced by the imposition of operational requirements. Typical measures, for example, might include: work instructions, safety training courses, personal safety equipment (PSE), risk assessments, safety indexes.

The "5 safety rules", which are now internationally accepted when working on electrical installations, are particularly important:

1. Insulate
All system components must be completely disconnected from the power system – including possible return voltages.

2. Secure to prevent reconnecting
Secure switchgear, e.g., with interlocks or warning signs, to prevent unintentional reconnection.

3. Verify that the installation is dead
Using suitable measuring equipment, test each conductor to ensure it is not live. A voltage may be caused by a feedback loop or another test set.

4. Carry out grounding and short-circuiting
First connect to the grounding arrangement and then to the system component. All connections must be securely connected and short-circuit proof.

5. Provide protection from adjacent energized parts
If adjacent live parts cannot be switched off, cover or shield them.

Safety standards are at the heart of personal safety in the development of tests sets. IEC 61010-1, ISO 13849-1 (incl. IEC 61508-3), and EN 50191 are particularly relevant.

IEC 61010-1: Safety requirements for electrical equipment for measurement, control, and laboratory use
IEC 61010-1 specifies the general safety requirements for electrical equipment for measurement, control, and laboratory use. Its objective is to minimize the risk for users and the environment. Among other points, it stipulates the protective measures that will eliminate electrical, mechanical, and thermal hazards, and prevent the spread of a fire that might be caused by a faulty device.

ISO 13849-1: Functional safety
This standard describes how the control components (including software) that are important in terms of safety have to be configured. The objective is to minimize the chances of a dangerous error occurring. The standard has been extended by the inclusion of IEC 61508-3 for the software. It applies regardless of the type of technology, in other words it applies to electrical, mechanical, and hydraulic systems.

EN 50191: Erection and operation of electrical test equipment
This European standard governs the installation and operation of electrical test installations. Among other things, it includes requirements for protective measures, personnel, testing procedures as well as, for example, the signaling using lamps (red/green) to indicate operating statuses.