pat testing computers with primetest 100

[Derek B]

Hi, Its my first post so I hope somebody can help.
When trying to pat test computers at my school I always get a fail on the earth leakage test.
The primetest 100 I am using is rated at 200ma so it wont fry the motherboards etc.
can anyone explain why the earlh leakage test fails on all computers I have tried?

[verstapp]

my immediate thought is surge protection in the power supplies.
selecting a test which takes account of this, IT CLASS 1 MOV for instance, should help.

[Paul - Cotswold PAT]

Surge protection will only effect the insulation test, not the earth continuity which is not affected.
I assume the computers you are testing are desk top computers, not laptops? Also, that you are testing the computer tower/casing? Are the supply cords detachable, are they IEC leads? If so, test the leads first seperately before testing the casing. From what I know fo the PT100 they have a fixed setting for earth continuity. If the leads are very long, the test result, even though a pass may show as a fail as the PT100 cannot allow for the extra resistance through the flex.
Just a few thoughts, hope it helps.

[stu at ats]

Derek,
The earth leakage test limit for portable or hand-held class 1 equipment is 0.75mA (the factory set pass/fail limit of the primetest 100).
Other Class 1 equipment has a maximum (except heating appliances) limit of 3.5mA.
You need to look at the measured values and ensure the reading is between 0.75mA and 3.5mA.
Suggest you purchase the latest IET code of practice 4th edition.
Earth Leakage is a complimentary test to the insulation test, and should not be confused with IEC leads surge protectors etc.
Lastly even a PAT tester with a 25A test current option, used correctly, will not fry motherboards.

[Paul - Cotswold PAT]

Derek,
Stu above has it right, sorry, I misread your original post and got myself all tied up with Earth continuity. I obviously need more sleep!

[Grizzly]

The Primetest 100 doesn't do a 'true' earth leakage test, which would energize the EUT to 230V ac. Rather, it does a much lower voltage version of the test, at 40V ac, so that might have something to do with it. Then again, it might not...

However, I wouldn't recommend performing a 230V earth leakage test on computers, as to get any meaningful result, you'd have to start the computer booting. It's doubtful that the test would last long enough for the computer to complete booting, so it would crash out mid-boot. Even if it did complete the boot cycle, the test wouldn't last long enough to properly shut down the computer before the power was cut. Neither scenario is particularly conducive to a healthy computer...

[Derek B]

Thanks for all the help.
Merry christmas one and all !!!