EN 50191 is about providing protection against electric shock. The standard addresses specifically the erection and operation of electrical test installations in the workplace. It incorporates provisions from 11 other European Norm standards to provide details of good engineering practice when testing electrical equipment.

Two harmonized standards are referred to in the text of EN 50191: HD 384 for voltages up to 1000 V and HD 637S1 for voltages exceeding 1000 V. Both documents are used when considering equipment for which the power supply does not fall within the scope of EN 50191. Table I lists other standards used as normative references. It is important to note that EN 50191 has no reference to CE marking or any other manufacturing product standard.

The new European standard was implemented March 1, 2001, and its introduction will require the withdrawal of all conflicting national standards by October 1, 2002. Compliance with the practices and conditions described in EN 50191 will, therefore, become a necessary requirement to show due diligence and best working practices.

Compliance with the standard will enable an organization to demonstrate that it has adopted the best working practices. Appropriate due diligence will be regarded as having been adopted through these best working practices with the application of electrical testing by skilled or trained personnel.

This combination enables risk assessment to be kept at an optimal level. EN 50191 sets the standard for the erection and operation of electrical test installations throughout Europe, which allows safe working conditions to become common practice in all member countries and judgments to be made against a common norm.

Most organizations involved in the manufacture of electrical or electronic products and components will need to comply with EN 50191. Compliance is not required only if contact with live parts presents no danger. The standard defines four conditions at live exposed points when conformance is not required. These conditions are associated with voltage, current, discharge levels, and the frequency of the product under test.

The protective measures vary between different locations. On production-line test stations, for example, safety requirements differ depending on whether the test location has automatic protection against direct contact with live parts (such as full test enclosures). However, in each case EN 50191 provides a variety of technical protective measures on insulation levels, for example. Physical requirements are given in the shape of barriers, signals, and lamps.

The standard details five definitive test installations and the levels of protection required.

Test Station with Automatic Protection against Direct Contact. The use of test enclosures encapsulates the device under test (DUT) and prevents any contact when the tests are
applied.

Test Station without Automatic Protection against Contact. This could be a product that is too large to allow the use of a test enclosure. Prohibited areas must be used with fixed barriers to prevent access to the DUT from unauthorized personnel.

Test Laboratories and Experimental Stations. Each test area within a laboratory must be individually protected and isolated. A common emergency cutoff could increase risk to another area, increasing possible hazards at other test stations.

Temporary Test Station. A skilled engineer conducts testing on a client's site or sets up a one-time test station to test a specially designed device. Individual assessment of the area and exclusion zones must be implemented to provide for the specific location and situation.

Test Station without Test Personnel in Permanent Attendance. In situations in which automated production line or life testing is undertaken, full protection from live parts with an automatic cutoff must be used in every position of entry to the DUT.

The implications of EN 50191 will be far-reaching. Any organization that carries out electrical safety testing is affected. In addition to test stations linked to production lines, test laboratories, experimental test stations, repair and service locations, and temporary stations are all covered by EN 50191.

The standard covers a range of safety measures designed to protect against electric shock in the erection and operation of electrical test installations. This range of general but vital safety measures includes:

It is apparent that the standard covers not only testing equipment but also testing methods for the entire electrical test installation. EN 50191 clearly defines specific instructions for the size of test areas and for the use of protective barriers and devices to be fitted, including indicator lights and appropriate signage.

Table I. Standards referenced in EN 50191.

Conforming to the requirements in EN 50191 will be new for many organizations, but it includes many safety controls and practices that should already be in place to meet existing regulations. The first step in complying with the standard is to perform an audit of testing operations. It is important to assess how to achieve compliance and to determine whether changes in testing methods could reduce the work or resources needed for compliance.

In addition to information on test installations, EN 50191 also provides guidance on the level of competence required of the personnel performing the tests and of those who control the testing operations. Staff responsibilities are defined in the standard as:

The standard calls for ongoing training and continual assessment of these persons to ensure compliance.

The standard includes a series of fundamental measures for all test locations to ensure protection against electric shock. These measures include providing emergency switch-off procedures, preventing automatic energizing, protecting against residual voltages, and implementing other specific requirements. In addition, further measures are described for different test environments, which vary with the level of risk associated with them.

For some test stations, a prohibited zone and installed physical barriers are required. However, a prohibited zone is not required when a test station is equipped with automatic protection to prevent direct contact with live parts. Areas that do not represent test stations with automatic protection require additional measures to address safety issues such as the use of test probes, work-area design and materials, protection from indirect contact with electrical equipment, and restrictions to 3-mA leakage current on the high-voltage side.

The harmonized European standards covered by the Low Voltage Directive (EN 60335) or Machinery Directive (EN 60204) are concerned with the design principles and electrical safety of particular items or groups of electrical equipment. These directives are product-specific. EN 50191, however, establishes safe procedures for testing all types of electrical equipment. It is location-specific and primarily concerned with the safety of personnel using the test area and preventing entry to unauthorized staff. Both types of standards apply. They are not alternatives.

EN 50191 establishes a common level of safety for electrical testing installations throughout Europe. It covers voltages from as low as 25 V. Instrument suppliers must be prepared to offer solutions for the safe use of their test instruments. End-users must satisfy the need for designated test areas, skilled and trained operators, and risk assessment of operations.

Although there is no requirement for test instruments to be labeled to indicate compatibility with EN 50191, instrument suppliers should be actively involved with helping end-users attain product conformance to the standard. Suppliers should ensure that ancillary safety devices easily interface and should provide good guidance in their documentation. Test stations should include safety enclosures and automatic protection to make conformance easier for end-users.

Penalties are not directly applicable for noncompliance to EN 50191, but failure to work to best practices could be interpreted as failure to observe the Electricity at Work Regulations of 1989 or the Health and Safety at Work Act of 1974. Therefore, penalties could be derived from failure to comply with these regulations.

In the United Kingdom, policing will likely be handled by the Health and Safety Executive office. This office will refer to EN 50191 for best working practices during assessments of the safety of testing areas. Equivalent bodies throughout Europe will probably establish similar procedures.

This new standard provides guidance on how to prepare most environments so that they protect against electric shock. Its implications are far-reaching, covering installations at manufacturers' production lines, laboratories, test houses, and other test environments. Compliance with the practices and conditions described in EN 50191 will become a necessary requirement to show due diligence and best working practices.