In April 2005 the NZ Ministry of Education issued an advisory notice to schools encouraging them to carry out electrical testing of portable appliances. The suggested means for doing this is a Portable Appliance Tester (PAT). This work can be carried out by a competent person – who could be a suitably trained staff member in a school, not necessarily someone holding an electrical certificate. The legal requirement for schools to carry out this testing basically comes from Occupational Safety and Health (OSH) and the MOE guidelines cite the specifications of AS/NZS 3760:2003 as the basis of the testing procedures to be followed.
I’ve started looking at PAT checks at our site and have noted some things already which may not be too obvious. One is that modern laptops, for some reason, are earthed and should therefore be tested as Class 1 appliances. When we took our first delivery of TELA laptops several years ago, they all used a 2 core mains lead and plug into the mains power adapter, meaning they were double insulated, as you would generally expect for a plastic cased device that runs from both battery and mains power. The latest Toshiba and HP laptops, however, all use a 3 core lead with 3 pin plug and socket fitted. When I put these on the Class 1 test, they all proved that a metal connection on the laptop case (such as the VGA connector screws) is electrically connected to the earth pin on the mains plug. Why the manufacturers have changed from double insulation to earthing, I don’t know, but if a laptop doesn’t have the double insulated symbol on its power supply then it must be considered earthed and tested as a Class 1 appliance.
Secondly, the laptop, both physically and electrically, consists of three parts: the mains cord, power adapter and laptop itself. The test is carried out using an earth connection onto the laptop with the mains cord plugged into the PAT, and then stickers are applied to each of the three parts, otherwise how can you be sure which part the sticker applies to (as all three parts are separable and interchangeable with other people’s laptops)?
Thirdly, and this is relevant to the above, the retest interval for flexible cords, like the power cord and the adapter, is less than the laptop itself. The laptop can possibly be given a retest interval marked at 3 – 5 years. The power cord and adapter, perhaps just 12 months. You may, however, need to connect all three parts together to do any retest just as I did with my original tests. The trickiness of this is to know which part actually failed if the tester shows such a result.