Steve Dunning, Managing Director of Martindale Electric, looks at how to ensure you are carrying out Portable Appliance Testing (PAT) correctly.
Designed to help raise the standards of electrical safety in the workplace, portable appliance testing ensures that electrical appliances and equipment which have been classified as ‘portable’ are safe to use.
For the purposes of PAT testing, portable appliances are defined as those that use a flexible cable or plug and socket. This means if an appliance has a plug connected to a wall socket or generator, it should be PAT tested. This definition includes either hand-held or hand-operated equipment, intended or likely to be moved (refer to the Fifth Edition of the IET Code of Practice for full definition).
To help companies with their portable appliance testing strategy there are many commercially available PAT training courses. These are invaluable to help provide the necessary theoretical and practical knowledge to undertake testing and inspecting different electrical appliances.
When undertaking inspection and testing, a training course will provide the high level of knowledge needed and give invaluable information on the right test equipment to use, the ability to use it properly, plus the ability to properly understand the test results.
However, even for an experienced user of portable appliance testers there are 12 potential errors which need to be carefully avoided:
1) Not doing a visual inspection
Before you measure the condition of an appliance, make sure that all its parts are there—and in good condition. Any signs of damage should be reported along with any dents/scratches on the casing. These can indicate that the appliance has been dropped or handled incorrectly at some point in its life. If the cable shows signs of wear, or is not plugged in properly, this should be recorded as it could indicate that the appliance is unsafe.
2) Not doing the tests in the required order
If on a Class 1 appliance you do the insulation test first, you don’t know if the conductive earth path is good. That’s because in Class 1 appliances most PATs use the earth wire as the return signal path, which is why you don’t need to use a probe for the insulation test. If the earth path isn’t tested and proven good, you can’t rely on the insulation test.
3) Forgetting to switch the appliance on
Think about a situation where the live wire is broken inside the appliance and touching the outer casing. When you do the insulation test, everything inside the appliance should be at 250V/500V. The tester detects (via a probe or the earth wire) any voltage escaping to the appliance housing. But if you haven’t switched it on, the voltage can’t get through the live wire, nothing will escape and you could have an incorrect pass of a dangerous appliance.
4) Touching the appliance
The truth is most appliances pass the insulation test, so you get into the habit of holding drills, etc, to make it easier to hold the probe in contact. But there’s always the risk that one day the appliance insulation fails and results in a shock.
5) Only doing 1 earth bond test
If an appliance has multiple, apparently isolated, outer parts with separate earthed paths, each one needs to be separately measured.
6) Taking an average reading
If you have multiple earth paths, don’t take the average reading – it’s the worst case that matters.
7) Trying to do an earth bond test on a Class II appliance
This will, of course, fail as Class II appliances have no earth. This is a very common mistake and causes a large number of calls to technical help lines.
8) Only doing one insulation test
For the reason outlined in point 5 above this is a common fault. At how many places on a power tool could the insulation break down? Obviously at the chuck, but what about the ventilation slots, the trigger, the assembly screws, the speed control?
9) Not checking the fuse is conducting (see point 3 above)
You don’t have to do a separate fuse test – the function test will prove that the appliance is both on and the fuse is okay.
10) Failing to do a functional test (powering it up)
Some entry level PATs don’t have the ability to power up the appliance. If your PAT tester doesn’t, then plug the appliance into the wall socket (after PAT testing) and make sure it works properly.
11) Not testing at the correct voltage
It is quite common for people to make the mistake of performing a 500V test on surge protection extension leads. These require a lower voltage 250V test, which is especially helpful when testing appliances with surge protected circuits, such as sensitive IT equipment at 250V.
12) Not calculating the correct pass level
Many appliances use longer power cables than those specified by the manufacturer – therefore note the current pass level for an appliance with a longer power cable can be determined by a calculation available in the PAT code of practice.
So, given the importance of PAT testing and the wide variation in operating environments and equipment, it is extremely important to ensure the right kit is selected to suit the application. For example, to enable minimal disruption some appliance testers are small handheld devices and therefore highly portable, enabling appliances to be tested on site rather than back at a central workshop.
When choosing a tester, ensure all bases are covered - not only appliances but also mains extension leads – and consider early in the selection process accessories such as labels and adaptors for appliances. Ideally, your unit will have a good range of readily available accessories for use across a wide range of applications.
Visit https://martindale-electric.co.uk/product-category/pat-solutions/ for further information and tips.
