pat testing computers

[mattthesparks]

could someone please detail a test sequence for computers using a pat tester, with test voltages/currents.

 

[ericmark]

Any items with a switch mode power supply and RF filters one has to be careful not to blow the capacitors so often the IR tests are limited to 250v rather than normal 500v.

Also because often the earth connections on IT equipment are made vie the tracks on the printed circuit boards if the design is unknown then better not using 25A to test earths but 250ma test is very common.

However lead sets will still be tested like any other extension lead.

The problem with many PC's is the sticker that comes with the power supply that tells one it has an isolation transformer often is no affixed to the outside of the case. You have to decide when that happens if your going to fail it or not. I think most people don't worry.

Laptops often have extra low voltage supplies and a step down inverter often class 2 and you have to decide if you like the way it is marked up most just give them a visual check.

At the end of the day if your signing paper work you have to decide if you think it's safe or not. We can get very pedantic and find all sorts of reasons to fail the PC but can't really see the point. However I do look at leakage and if over 1ma I do note it and over 3.5ma is a fail. Really 1ma should be a fail but seems common for IT equipment to exceed 1ma.

The three figures 1M ohm, 1ma, and 3.5ma don't seem to add up but 1M ohm is a DC measurement but the 1ma is an AC measurement. I have found new equipment with 2ma leakage again you have every right to fail it you have to decide.

 

[Monkeh]

The problem with many PC's is the sticker that comes with the power supply that tells one it has an isolation transformer often is no affixed to the outside of the case.

I feel I should point out that PSUs typically don't come with any such sticker. Certainly not one you're meant to put on yourself.

 

[Grizzly]

For Class I PC

Full Visual Inspection of both lead and PC

For supply cord:

Earth Continuity test, pass limit according to nominal conductor CSA & length of lead (see IEE CoP, Table VII.1, page 124)

Insulation Resistance test @500V, pass limit 1MΩ

Polarity check.

For the PC:

Earth Continuity test
test current in the range 20mA - 200mA
Pass limit is (0.1 + R)Ω where R = resistance of the pc in the supply cord (from earth continuity test of the lead!).

Insulation Resistance test
test voltage 500V dc is fine if the appliance has been constructed to BS EN 60950.
If not, or if you are unsure, then either do the IR test at 250V (if the portable appliance tester has the facility), or do the Protective Conductor Current test (aka Earth Leakage).
Pass limit for IR test is 1.0MΩ. Pass limit for leakage is 3.5mA (don't know where Eric is getting his 1mA from).

 

[ericmark]

Yes I made a mistake scanned BS7671 and found 612.5.2 and did not check what it was taking about and now realise it is earth free location.

 

[Grizzly]

Yes I made a mistake scanned BS7671...

Eric, just a thought, but it might be an idea for you to stop looking at BS7671 when dealing with PAT questions.
It doesn't cover in-service inspection & testing, and just leads to you giving out innacurate information.
It's the IEE Code of Practice you should be using, not the 17th.

 

[OwainDIYer]

If you refer to the code of practice and the HSE guidance note, most office PCs don't need testing as they are replaced from new as or more frequently than the test interval.

Visual inspection yes, flex test yes, PC visual inspection sufficient.

 

[holmslaw]

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[ericmark]

Very good point. Although they still need to appear on the equipment register.

If they are kept over the 4 years recommended inspection period however we can find faults which were there from new but by then out of warranty period and so where I worked they were tested when new.

 

[plugwash]

Thats what I thought, also I know some companies find it cheaper to replace all the leads than test them.

My question to them would be why do they trust the manufacturers of bottom of the barrel IEC leads (I would guess that they aren't exactly buying quality products if they are finding it cheaper to replace than test) to supply a fault free product?

 

[holmslaw]

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