pat testing tactile buttons

[macca22]

Hi,

I'm about to start training on pat testing, and I have already got a good fairly understanding behind it all but the one thing that has always confused me is when it says the appliance must be switched on. If the appliance has no switch, and it is a touch/tactile/soft press switch, then is the appliance already on, as would be in standby so to speak, or is that not classed as on for the test and if so, how would you test this item?

I'm talking about a TV for example, which has a "joystick" underneath the tv, but is in standby whe you turn it on at the wall.

 

[Doc Hudson]

I think you will find most modern TV,s are double insulated, as such there will be nothing to test in relation to earth continuity or leakage to earth. So other than a visual check and confirming the correct fuse is in the plug there isn't a fat lot to check in relation to Portable Appliance Testing. You need to sit back and think about what are the actual tests you are doing on an appliance? What is their purpose? and what are you aiming to verify once it is complete? Bit like asking how to test the oil level on an electric car.

Doc H. 

 

[Geoff1946]

PAT on electronics is fraught with problems. Apart from getting misleading results you can do expensive damage. 

My take on anything with electronic switching, normally on in a standby mode, is that it is already ON. Only mechanical switches need to be checked to be ON.

(The simplistic "switch it on" instruction is for basic appliances. e.g. a kettle, or toaster, where the highest fault risk parts are physically isolated until the switch is put on).

Much electronic gear is class 2 so there is no earth continuity to check. By all means do an insulation check to exposed metalwork but be very careful what voltage you use, as low as possible, and never, ever, do a flash test.  90% of the safety checking of class 2 is by ensuring that the flex and enclosure are undamaged and that some clown hasn't used a 13 amp fuse for their bedside clock or desk lamp!

(Oh yes they do!  When you start doing PAT you need a large box of 3amp fuses, but you will never have to buy a 13 again.)

Where there is an earth connection to an item it may or may not have continuity of the to exposed metalwork. Audio and IT items are commonly like that. Where there is continuity take care to use only low current test or you can easily burn out circuit boards.  -  Always think what your tester is actually doing.     - For testing say a kettle, it pushes something like 20 + amps down the earth and to the body to ensure good connection. That's OK, but do the same to an audio amplifier and you will probably need a new one.

 

[NozSpark]

You'd only power up the equipment during a leakage test,,, my tester allows you to alter the "test" period so I could increase it to a duration that allows me to turn said bit of kit to turn on and carry out the test