PAT testing PC's and other sensitive equipment

[oharaf]

Hi Folks

Would like a definitive answer on this, have done some reading around and getting conflicting answers.

When carrying out PAT testing on PC's etc should you ONLY do Earth Bond test?

As the tester delivers 500Vdc (and option for 250Vdc) surely the risk of damaging the equipment is higher and so Insulation resistance is a no no!!

Cheers

 

[luminaire]

On Pcs and other sensitive equipment I usually do an earth continuity check @ 100mA and then an earth leakake test @ 6mA, as long as it is <3.5mA it is a pass.

 

[Grizzly]

Have a look at the IEE Code of Practice (3rd Edition).

For IT and other sensitive kit, you should be doing the 'soft' version of the earth bond test, which has a test current in the range 20 mA - 200 mA (page 74).

Only IT kit that complies with BS EN 60950 will definitly be able to withstand a 500V insulation test.
If it doesn't, or you're not sure, do either a 250V insulation test, or a Protective Conductor Current test (pages 75-76).

The IEE CoP is about as definitive as it gets for PAT.

 

[ericmark]

IT equipment often has a track on the printed circuit board for earth connection and 25A will melt the track so a low current test is done.

Also often they use switch mode power supplies and feeding a capacitor designed for 339 volt peak with 500 volt can cause them to fail sometimes with dramatic results bits of electrolyte soaked paper every where so again leakage test is done.

Leakage can be a problem if I am presented with paper work to confirm by design it has high leakage then I will pass but no paper work then fail.

Lack of

Isolation sign

• ericmark
• 12 Mar 2009
• 10

sign in visible position is biggest problem with PC's as the peripherals which plug into USB are often not insulated and in theory you may get 230vac on the output of the switch mode power supply under fault conditions if it does not have that sign. But since it is the peripheral one would get shock from not PC I have never quite worked out if missing sticker is a fail?

On a new power supply they come with spare sticker to put on outside of PC which the builders of the PC often don't use and one would really be failing it on lack of sticker.

 

[oharaf]

Thanks for that guys, very helpful.

Will get a copy of the guidance booklet.

 

[Spark123]

then an earth leakake test @ 6mA, as long as it is <3.5mA it is a pass.

What does the @6mA part mean? I thought the tester just powered up the appliance, measured the current flowing in the CPC and in some instances converts it to what it would be at 240v - I know the PAT 4 DVF does the conversion thing as have had appliances fail with 30mA leakage but didn't trip the 30mA RCD - bit of a head scratching time!!