PAT tests on a PC

[AVspark]

I have just started PAT testing, got a megger PAT420 due to the available work that i can use it for.

I have been getting to grips with the tester and have come up with 2 questions.

1. Tested a CRT monitor and the computer tower seperately, did the leads first then plugged them into the appliances. I did the reduced earth continuity at 200mA and got a reading of 0.15ohms for both pieces of equipment. The only available earth point on the monitor is the ground of the VGA plug which is connected to the chassis of the monitor. I did the same test on the computer tower and came up with the same reading. I tried various places on the tower and got exactly the same reading both times. As they are both class 1 pieces of equipment i technically need to fail them. I know the power supplies in computers will always generate leakage. is there any way to get around this??

2. There are a number of suggestions as to doing Insulation resistance/Leakage tests on PC's. Any advice on this would be helpful. I have got a number of churches to test and they have a number of PC's. I don't want to be responsible for any damage to them.

 

[tony mc]

Have you deducted the resistance of the lead that was plugged into the devices.

For appliances with a supply cord you need to looking at (0.1 + R )

IMO with that reading you have a earth point but need to know the R of the lead!

Have a look in your codes of practice and you can calculate the resistance etc there are even tables giving you the CSA and resistance with regards to lenth!

Welcome to the forum!!!

 

[AVspark]

I didn't take into account the lenght of the supply supply cable. They are both 2mts and according to the table will pass no problem. I took the clip off the plugs during the test just to check the reading to prove the earth. Seems the obvious thing to do when i have been taking longer leads into account for other appliances.


Thanks for the reply. Will retry the actual test on the same computer tomorrow, hopefully this time will pass.

 

[i=p/u]

i done my kettle with megger 1553 cliped the earth pin on plug and touched kettle with probe and got 0.35 so no way my lead resistance is .25

 

[i=p/u]

i have actually got my first pat job comming up and i need to get a pat tester... i do think i will only be concerned with earth bond and insulation resistance.. and a good visual

 

[AVspark]

Yeah, i am thinking of the continuity and insulation resistance. Forget about the power on tests, pc's have way too much stuff inside that is easily blown up with the wrong test. Mind you still hesitant to do the IR test on older PC's, just in case.

 

[tony mc]

Looks like you on the look out for a new kettle then unless the kettle lead was around about 16 meters long!!

 

[i=p/u]

yep, sure am not even allowed a cup of punjanna at 6am cause it has got very loud, just out get out , theres your lunch go get me money homm e

 

[AVspark]

I tested a kettle the other day and got <19.99. Needless to say the test got stopped and the element got a few scratched in the side to cut throught the scaling. Retested fine. I tested another kettle and with a 25a Bond and probe. I kept getting a reading slighty under then slighty over. Did the test about 8 times before i actually got it to pass. Had a really narrow neck so couldn't get my hand in properly to scratch away the limescale. If the kettle is a cordless that sits on the base is there any corrosion or film on the earth contact between the kettle and base itself that is giving that reading??

 

[i=p/u]

i didnt even empty it i just touch the metal casing on outside, i have looked at pat testing since i done the course last year.. need to scrub up

 

[oldtimer]

So what is the thinking behind the insulation test on a PC or PC type equipment

 

[Marnik]

Never do insulation test on IT equipment [500V ] insulation Res test could fry the PC , do it at 250V ? why?? Once you done a proper IEC lead test, (earthbond/insulation/polarity) all you have to do is a earthbond test at 100mA to the case of the PC or Monitor

 

[AVspark]

I have done and IR test on a couple of computers at 250V, keep hesitating before i hit the test button just in case. Both times i have connected the computer back up and booted it up, just to make sure it is working. I think in future i will just be doing a bond test at 100mA. If the IEC passes the IR test no sense in checking it a second time. I have been testing a lot of audio equipment and have been doing a bond test at 100mA and then doing the leakage test instead of the IR test. I guess after testing the IEC lead, i don't technically need to do the leakage test.

 

[Tonkatoy27]

Cordless kettles are a bitch, the scaping earth contact is so small on most of them it increases the value of the earth test to fail proportions if tested anywhere on the kettle body. I've got a shop as well and have tested new kettles with 0.2ohms or higher. If it's high, retest at the little copper contact coming out of the 360 degree base connector, if this is much lower then common sense kicks in and it's just the way it's designed.
After having a subby destroy a £2000 veg prep machine at the school kitchen we now don't insulation test ANYTHING that might have electronics in. (with ELECSA's approval) If the bloody testers would just connect phase to Neutral and then test to earth we wouldn't have a problem.

 

[tony mc]

Hi Tonkatoy

After having a subby destroy a £2000 veg prep machine at the school kitchen we now don't insulation test ANYTHING that might have electronics in. (with ELECSA's approval) If the bloody testers would just connect phase to Neutral and then test to earth we wouldn't have a problem

What type of tester are you useing as I was was under the opinion that all PAT instuments connected the Line & Neutral together when performing a IR test on all voltage ranges.

 

[Tonkatoy27]

From memory I think it's a Seaward primetest 300 or 350, intresting if that is the case. Even if they do it didn't stop that veg machine from being toast. Electrolux design said it would cope no problem, Lux tech said do not under any circumstance megger it ith any voltage. If they can't agree what chance did we have!

 

[oldtimer]

I have a Kewtech KT71 and the way I am reading it that this tester shorts L-N together before a IR is this correct as I would not want to make a mistake

 

[ohreally]

I have a Kewtech KT71 and the way I am reading it that this tester shorts L-N together before a IR is this correct as I would not want to make a mistake

'Tis my understanding. I'm not aware of an instrument (pat) which differs.


BTW, was in your neck of the woods earlier today - busy, busy, busy. Do you know why the road around Holyrood park was shut off, kinda wasted my day out a bit.

 

[Tonkatoy27]

Hmmm, thats interesting. I just presumes PAT testers didn't do that because of all the issues with 'will i or won't I blow up a pc on an insulation test' conversations. According to my ELECSA assessor if we do insulation resistance tests on installations by connecting L to N then it is impossible to damage anything. Thats obviously rubbish then.......

 

[oldtimer]

'Tis my understanding. I'm not aware of an instrument (pat) which differs.


BTW, was in your neck of the woods earlier today - busy, busy, busy. Do you know why the road around Holyrood park was shut off, kinda wasted my day out a bit.

Because Hoyrood Park is a major thorough fare during the week any work needing done on it or around it is done at the weekend I was down Leith today looking at a job so I went via the High Street as I know to stay away from HP because of works or weekend drivers