Psu and pat testing

[chrbb]

Right I know this has been discussed before but I need to know what fellow technicians do in the same situation as me.

 

Sole technician, no onsite Pat tester - I thought I had a failing psu in a problematic computer, so I swopped one out from an idential computer to test it. Psu returned to original computer. Problematic computer solved by installing graphics card as it was onboard graphics that has failed, so original psu put back in and computer now working.

 

However last pat tester we had informed me that when I replace a psu in a computer it should be pat tested before returning to general use. What does everyone else, in the same situation with no onsite Pat tester, do?

[Hacksawbob]

Say nowt, It has returned to the original tested configuration and will be tested in the routine testing procedures. If its really an issue then keep a separate PSU to one side for testing purposes and/or spend the £300 for an in house tester. Although you will probably get asked to do the whole school if you go down that route if the T+Cs of your contract allow for it, could get onerous!

[powdarrmonkey]

Take formal guidance from your SMT. Testing is not a legal requirement (contrary to popular belief), but providing equipment that is safe for a competent person to use is (hence an often-blanket policy that it must be PATed, because this is cheap and convenient). It's up to your school or LEA's local policy, and if they require it to be tested they must provide the means to do so.

[Jamman960]

If we're talking about having a computer re-tested because its had its psu removed and put back in then I can't see how anyone can insist on a re-test, even if the psu has been swapped for another previously tested PSU I'd still query the need for a re-test. you'll be carrying out a visual PAT test while installing it and it'd have already been declared electronically safe. As long as your happy that it looks ok and you've not dropped or have any reason to believe that it may have been damaged then it should be safe.

 

If you've replaced he PSU with another untested/brand new PSU then I guess you'd need to treat it as you would any new bit of kit, either insist on pat testing before it goes out or ensure its pat tested on the next cycle.

[chrbb]

I've put the computers back into circulation as the psu was previously tested and deemed safe. But I'm unsure as to why he said a new Psu would need testing, is it the integrity of the new part or that I might muck up putting it in and trap a few wires or something?

[synaesthesia]

how does that work? PAT testing on a PC is a visual inspection only - the only part that can be tested by any means is the cable itself, not plugged into anything (if that's even possible).

[powdarrmonkey]

If we're talking about having a computer re-tested because its had its psu removed and put back in then I can't see how anyone can insist on a re-test, even if the psu has been swapped for another previously tested PSU I'd still query the need for a re-test. you'll be carrying out a visual PAT test while installing it and it'd have already been declared electronically safe.

 

Wrong. Part of a formal PAT is the earth bond formed between the metal case and the case of the PSU. If they are exchanged, their characteristics change.

 

As long as your happy that it looks ok and you've not dropped or have any reason to believe that it may have been damaged then it should be safe.

 

Wrong. The installation matters as much as the visual.

 

I've put the computers back into circulation as the psu was previously tested and deemed safe. But I'm unsure as to why he said a new Psu would need testing, is it the integrity of the new part or that I might muck up putting it in and trap a few wires or something?

 

See above.

 

how does that work? PAT testing on a PC is a visual inspection only - the only part that can be tested by any means is the cable itself, not plugged into anything (if that's even possible).

 

Wrong. A PC is a class 1 item, so it gets*

 

1. Formal visual inspection
   
2. Earth bond test (100mA conductivity, less than 0.10ohm resistance)
   
3. Fuse and polarity test
   
4. Insulation test (must be >10Mohm)
   
5. Powered run test within manufacturer's stated current requirements and acceptable leakage
   

 

*at least, these are my local requirements. Yours may differ.

 

The IEC lead gets a separate, aptly-named IEC test.

 

 

This is precisely why you should be asking your SMT instead of relying on folklore.

Edited January 25, 2010 by powdarrmonkey

[Andrew_C]

Powered run test within manufacturer's stated current requirements and acceptable leakage

This is the only bit I'd differ with; the PC may not complete a boot cycle, and thus the run test may be skipped.

 

That said, I know what I'd do in the OPs situation, but I'll not say in public.

[powdarrmonkey]

This is the only bit I'd differ with; the PC may not complete a boot cycle, and thus the run test may be skipped.

 

I've come across testers with an extended run time, so it can be done. But if I'm going to handle the machine, I'm far more worried that it passes earth and insulation

[chrbb]

Wrong. Part of a formal PAT is the earth bond formed between the metal case and the case of the PSU. If they are exchanged, their characteristics change.

 

Even with the same psu reinstalled?

[powdarrmonkey]

Even with the same psu reinstalled?

 

Perhaps. If the screws holding it in place aren't tight, for example, the resistance between it and the case changes. That affects the earth bond.

 

This is academic though. You should still be getting an answer from SMT (then it's their neck on the line, not yours).

[mjs_mjs]

 

1. Formal visual inspection
   
2. Earth bond test (100mA conductivity, less than 0.10ohm resistance)
   
3. Fuse and polarity test
   
4. Insulation test (must be >10Mohm)
   
5. Powered run test within manufacturer's stated current requirements and acceptable leakage
   

 

 

This is pretty much what a PAT test is, but there are more things on our in house PAT tester, but i'm not trained to use it. Any change to a PC should in theory require a PAT test, as you have changed the make up. New equipment should also be PAT tested as it may have been damaged internally while in transport. But as with everything like this, the person doing the PAT test should decide what does need doing and when. If you don't have one (someone who's in charge of it) ask up you line management until someone gives you a definitive yes/no, or insist it gets done if your worried about it.

 

Most faults we will be dealing with as technicians will be ones easily identifiable by visual inspection, anything that is still suspect should go to an electrical engineer, along with yearly checks on most equipment that's in use. That's my professional opinion.

[powdarrmonkey]

This is pretty much what a PAT test is, but there are more things on our in house PAT tester, but i'm not trained to use it.

 

One of them is probably a flash test, which you most certainly do not do to a PC. Ever.

[mjs_mjs]

One of them is probably a flash test, which you most certainly do not do to a PC. Ever.

 

Yep, we have that feature. I remember the person telling me that he doesn't do that on our PC's. Or any other devices with low voltage elec's.

[powdarrmonkey]

Yep, we have that feature. I remember the person telling me that he doesn't do that on our PC's. Or any other devices with low voltage elec's.

 

That's because it's an application of 3,000V between the case and the live+neutral shorted together. It kills things if you don't understand it, and it's no longer recommended for in-service equipment by the code of practice, though I believe it's still done by manufacturers in controlled conditions.

[mpe]

Take formal guidance from your SMT. Testing is not a legal requirement (contrary to popular belief),

The idea of a yearly PAT test is actually on the myths section of the HSE's website.

but providing equipment that is safe for a competent person to use is (hence an often-blanket policy that it must be PATed, because this is cheap and convenient).

In some cases it can wind up expensive and inconvenient. Especially when external contractors are involved and/or someone is incapable of reading where the manufacturer has indicated that certain tests NOT be carried out.

[mpe]

Most faults we will be dealing with as technicians will be ones easily identifiable by visual inspection, anything that is still suspect should go to an electrical engineer, along with yearly checks on most equipment that's in use. That's my professional opinion.

Which is completly at odds with the HSE guidelines. in the case of computers a starting point of formal visual inspection 2-4 years and a formal test every 5 years (or not at all in the case of double insulated).

It's unlcear where the "every year" idea even comes from. It's also important that if leads are unplugged for testing they are plugged back in fully after.

[Jobos]

I find many PAT testers are con men as well, as today I saw a ActivBoard that was sporting a PAT test label!

[mjs_mjs]

Which is completly at odds with the HSE guidelines. in the case of computers a starting point of formal visual inspection 2-4 years and a formal test every 5 years (or not at all in the case of double insulated).

It's unlcear where the "every year" idea even comes from. It's also important that if leads are unplugged for testing they are plugged back in fully after.

 

I work for the council directly and they have an every year policy, so all of my lovely audio equipment that the centre has gets tested by some contracted numpty who sticks labels over serial numbers and fails some of it because it isn't grounded correctly, although it is.

 

At the school, almost every bit of kit we use gets a visual inspection as part of it's day to day maintenance so it's easy for me to say every year. Would i actually do one every year - no because if it's still working (ie no ones moaned to us) then it's probably still electrically fine. If it isn't is should trip an RCD/RCBO, so we get a call, and it gets an inspection to find a fault.

 

Anyway I/we go off topic. For swapping a PSU over, if it's new i wouldn't PAT test it. If it had already been PAT tested i wouldn't test it again for some time. If it's fitted correctly then there should be no real need.

[chrbb]

I spoke to smt about retesting the computers today, they have no idea what a psu is let alone what pat testing does and seem to be happy to leave the decision up to me as to whether the computers need pat testing. Appanrently there's no guidance from the LEA either. Thats the problem as a lone tech in a small school, you have to know everything and then make the decision!

 

So what I've decided to do is to take the two computers out of circulation until tested. My husband is an engineer, (he was an electrical apprentice, industry not domestic) and has explained at length that there should be no danger from anything that is earthed, but I think I should follow other schools procedures and make a 'corporate' decision and inform smt that interim pat testing is needed when a psu has been changed.

 

Replacement of other items, ram, hard drive etc don't require pat testing do they?

[mjs_mjs]

Replacement of other items, ram, hard drive etc don't require pat testing do they?

 

shouldn't do - there not high voltage so pose no dangerous risk and should not be accessible to the user to touch anyway. It should all be earthed to the chassis, which is earthed to the PSU, which should be earthed to the mains.

[powdarrmonkey]

I spoke to smt about retesting the computers today, they have no idea what a psu is let alone what pat testing does and seem to be happy to leave the decision up to me as to whether the computers need pat testing. Appanrently there's no guidance from the LEA either. Thats the problem as a lone tech in a small school, you have to know everything and then make the decision!

 

In the long run, if that's the case you're effectively taking responsibility (yes, it shouldn't be that way, because SMT are ultimately responsible, but I wouldn't put it to the test). I would hassle them, the governors and the LEA to do their research and write policy, then you can carry it out.

 

So what I've decided to do is to take the two computers out of circulation until tested. My husband is an engineer, (he was an electrical apprentice, industry not domestic) and has explained at length that there should be no danger from anything that is earthed, but I think I should follow other schools procedures and make a 'corporate' decision and inform smt that interim pat testing is needed when a psu has been changed.

 

This is wise. (Earthing isn't everything, but it is the last resort if a fault develops. The other measures that get tested should prevent any major problem long before that.)

 

 

Replacement of other items, ram, hard drive etc don't require pat testing do they?

 

No, not unless you've done something really weird, like wire them to the case

[mpe]

I find many PAT testers are con men as well, as today I saw a ActivBoard that was sporting a PAT test label!

Well it does have a PSU, with an unpolarised 2 pin connector...

I'll raise you some USB scanners, PSUs for a mobile phone and a bettery charger (both with plastic earth pins), a radio cassette player (also with 2 pin connector), several laptops and keyboards (of the musical variety).

[powdarrmonkey]

Well it does have a PSU, with an unpolarised 2 pin connector...

I'll raise you some USB scanners, PSUs for a mobile phone and a bettery charger (both with plastic earth pins), a radio cassette player (also with 2 pin connector), several laptops and keyboards (of the musical variety).

 

In those cases you are testing the power supply, not the board itself, and that's where the certificate should be attached since the supply can be detached from the device.

[mpe]

I work for the council directly and they have an every year policy, so all of my lovely audio equipment that the centre has gets tested by some contracted numpty who sticks labels over serial numbers and fails some of it because it isn't grounded correctly, although it is.

No doubt they also have a policy that "numpties" shouldn't be messing with the equipment in the first place As for the grounding issue they probably don't understand that grounding for EMI supression is nothing to do with grounding for electrical safety. Something which can result in expensive breakages in certain situations.