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Electrical Safety Testing

 

Overview

Periodic Appliance Testing (PAT) is the in-service inspection and electrical testing of portable electrical equipment to ensure that it is safe to use. This in-service testing is necessary for the safety of persons using the equipment and for the proper discharge of the obligations of both employers and employees under the Occupational Safety and Health (OSH) legislation of New Zealand.

Whilst the testing of electrical equipment to AS/NZS-3760 is not mandatory in all situations, compliance with electrical regulations and maintaining the safety of personnel in the workplace are both mandatory. In the event of an electrical accident, penalties brought against an employer under OSH legislation for failing to take appropriate safety precautions can be severe.

The NZ electrical regulations specify AS/NZS-3760 as a means of compliance so if an electrical accident occurs and you have not complied with AS/NZS-3760 as a minimum then an OSH investigation would be likely to determine that you have not taken all practicable steps to provide a safe workplace and could then use non-compliance with AS/NZS-3760 as the basis for a prosecution.

Example of Rationale for Periodic Inspection and Testing

The rationale behind periodic safety testing of electrical equipment and the determination of the most appropriate testing interval is demonstrated in this example for stage lighting equipment. Consideration of the type of equipment and the environment in which it is used results in the following facts...

  • Luminaires operate at high temperatures that can cause the insulation of wiring to become brittle.
  • Adjustment of luminaires is usually done at the top of a ladder where a minor electric shock could cause a fatal fall.
  • Luminaires are often still in service 10 to 20 years after manufacture.
  • Scenery being moved on stage sometimes collides with luminaires which may cause damage to the luminaires.
  • Luminaires are typically operated in positions that prevent developing hazards from being easily seen.
  • Well-meaning persons tend to effect substandard repairs in a spirit of "the show must go on".
  • Equipment is usually operating in venues where a large number of members of the public are gathered.

Therefore, given the nature of its use and operating conditions, it is reasonable to conclude that stage lighting equipment is likely to deteriorate to a hazardous condition and that such a hazard could go unnoticed for an extended period of time unless some form of routine testing is carried out. Clearly, using a procedure such as AS/NZS-3760 to reduce the risk of hazards developing and to detect any hazards that do develop would be a prudent step towards maintaining electrical safety.

Can We Do Our Own Testing?

The short answer, in accord with the AS/NZS-3760 standard and current legislation, is yes you can BUT, with few exceptions, it's definitely not something we would recommend.

Certainly it is easy enough to purchase a suitable test instrument and teach someone how to use it correctly but the testing is only half of the required procedure, the other half is the inspection. A semi-skilled person can see a cut cord or broken plug easily enough but what about the less obvious issues?

Consider this example...

An older model spotlight had its power cord accidentally damaged during setup for a show. It was sent to a local domestic appliance repairer, unfamiliar with theatrical equipment, who replaced the power cord and returned the spotlight in working condition and the spotlight was put back into service.

Several months later a semi-skilled person tested the spotlight using a portable appliance test instrument and the tests were passed ok. That person's inspection of the spotlight determined that it was in good electrical and mechanical condition. The spotlight was tagged and put back into service.

A short time later a person focusing the spotlight for a show received burns to their face and fell from the ladder resulting in serious injuries when the spotlight 'exploded' in their face.

What went wrong?

The orignal power cord was of a special type rated for high temperatures which had not been manufactured for many years. The repairer was not familiar with theatre spotlights and had never seen cable of that type before so thought it was just an old type instead of recognising it as a type with special characteristics. The repairer then replaced the power cord with a cable type typically used on domestic heaters believing it would be adequate as the repairer didn't know that the wiring in theatre spotlights is subjected to higher temperatures than typical domestic appliances. The insulation in the new cable deteriorated rapidly over several months becoming increasingly brittle at its point of entry into the spotlight body until, with normal flexing of the cable during focusing, the brittle insulation finally crumbled causing a short circuit with arcing and sparks that burned the victims face. The fright caused the victim to loose balance and fall off the ladder.

The accident could have been prevented if the periodic test and inspection of the equipment was done by a company familiar with theatrical equipment as they would have immediately recognised that the spotlight had an incorrect type of cable fitted and tagged it as having failed the safety inspection. Neither would this accident have occurred if the original repair work was done by a company familiar with theatrical equipment who would have used the correct type of cable for the repair.

A qualified and experienced electrical worker is much more likely to spot a problem than a semi-skilled person with basic electrical knowledge who has learned how to correctly use an appliance test instrument. As the example above shows, even a reputable appliance repair shop can get it wrong when they are handling specialised types of equipment that they are unfamiliar with. It would therefore seem unreasonable to expect a semi-skilled person to be able to get it right.

Recommended Practice

Adena strongly recommends that all electrical equipment be tested according to AS/NZS-3760 using a testing interval that suits your own situation. In most school situations annual testing of stage electrical equipment is appropriate. In a theatre where equipment is in frequent use a six monthly or even three monthly testing may be more appropriate. The general rule is simple; if your equipment gets hard use it should be tested more frequently, if it hardly ever moves then it can be tested less frequently. Whatever test interval you choose, document your decision and the reasons that lead to your decision then stick to it and make sure all the test results are recorded in a log book or a database of some sort.

For the reasons demonstrated above, we recommend that you have all repairs and safety testing of theatrical equipment carried out by a reputable theatre services company. Such a company will have the necessary skills and tools as well as ready access to the correct spare parts to enable them to carry out the work efficiently, cost effectively and most important - safely.