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TestPower discuss importance of positive protection against direct contact at electrical test workstations

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article image Workstation

According to TestPower , setting up a safe workstation for conducting electrical safety tests must meet the requirements of agency standards as specified by UL, CSA and EN. Addressing operator safety during a test is important as ensuring the safety of the end-product user.

The first challenge a manufacturer faces is finding guidelines on how test stations should be set-up. It is common to find that the individual responsible for setting up the test station may not have an understanding of electricity or the hazards involved. Lack of awareness of the potential hazards involved makes it difficult to protect the operator against potential shock hazards. Often the focus is on setting up the test area for maximum productivity.

Assembly operations may also be performed at the same workstation to balance the production line. This makes it critical to set up a safe workstation. Assemblers not involved with the electrical aspects of manufacturing the product could be exposed to electrical safety hazards.

Qualified personnel must have the skills to distinguish exposed live parts from other parts of electrical equipment. Exposed live parts are parts of the product which are energised and which the operator may come into contact with during the test.

Individuals responsible for setting up the workstation must be aware of the proper clearance distances for corresponding voltage levels. The operator should be trained in safety related work practices or procedures and in emergency, must have knowledge of procedures required to release victim from contact with exposed live parts or circuits.

A person setting up test stations must be able to determine the extent of the hazard and the personal protective equipment or job planning necessary to perform the task safely.

Standards require that conductive materials and jewellery should not be worn by anyone working on or near energised equipment. A test station cannot be considered safe without proper training of any individuals involved in or exposed to the testing. The test station needs to be configured to provide the operator with possible protection against exposure to hazardous voltages.

The operators can refer to the proposed European Norm Standard prEN 50191 Erection and Operation of Electrical Test Equipment for guidelines regarding the proper set up of an electrical testing workstation.

The European Norm Standard prEN 50191 Erection and Operation of Electrical Test Equipment has guidelines that are easy to understand as they address the set-up and operation of electrical test equipment.

The EN 50191 differentiates between test stations with positive protection against direct contact and those without. In a test direct contact, the device under test (DUT) and all live parts of the test apparatus have positive and full protection against direct contact while the equipment is in an energised condition.

An example of full protection is a test hood that covers the entire product and the test instruments, making it impossible for the operator to contact either during a test without de-activating the high voltage. Test stations without positive protection against direct contact should only be used if it is not possible to achieve positive protection.

Some reasons for setting up test stations without positive protection may be due to the physical size of the DUT or requirements to manually test multiple points, which could prohibit the use of an enclosure. However, testing of multiple points does not mean that positive protection cannot be used.

Several new safety-testing instruments are available with scanning matrixes that can automatically apply voltage to multiple points of a DUT without operator intervention.

EN 50191 recommends the following safeguards:

  • Barriers or walls to separate the test area from assembly areas. The distance between the barriers and any parts that could become live are specified in the standard in relation to the maximum test voltage.
  • Insulated enclosures or covers to prevent access to the DUT. These covers should be interlocked with the test instrument.
  • Indicator lamps and warning signs. These provide visual indications that can be incorporated in the test area to indicate the operating status of the equipment within view of all operators.
  • Positive protection to guard against residual voltage must be incorporated. This means that output shorting devices should be used to discharge any energy which may be stored in the DUT.

Following are suggestions to protect operators at stations that do not incorporate positive protection against direct contact:

  • Test stations should be separated from work areas. The use of walls and barriers should be constructed to protect the people standing outside the test area. The barriers should be constructed, so visual contact with the test operator can be maintained from outside the test area.
  • Test apparatus must be guarded against unauthorised use or unintentional operation. A lockout device should be incorporated into the design.
  • Emergency switching equipment should be incorporated. This provides the operator with a way to cut off all voltages that can result in danger. At least one of the devices should be located outside the danger area.
  • Test bench should be made of non-conductive material. This is required to isolate the DUT during the test. Two-hand controls should be implemented. If an insulated enclosure cannot be incorporated in the design of the workstation, the use of two-handed controls may be an alternative.
  • Two safety probes should be incorporated. The operator can either apply voltage to the probes by manual operation or release the live probes, which must insulate the user from the test voltage if it remains active. Some probes may include an automatic switching circuit which de-activates high voltage when the probe is released. Two safety probes are specified which require the operator to use both hands to test the DUT. This prevents the operator from contact with the device under test while the test is in progress.

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