IT PAT Problem

[Graeme Harrold]

Hi,

Had this barking mad fault twice now. Using a Fluke 6500 I started an auto test on a desktop computer. Lead passed no problem, plugged in to do a bond test at 200mA and the machine picked up an earth voltage ans halted the sequence. I pulled out a DMM and found 78VAC on the casing, which vanished when I pulled the printer (parallel) lead out. Both the printer and the computer passed wel within limits.

Then found the same with a home computer and printer. Holding my laptop in the crook of my arm, got a tingling sensation, initially thought it was something scratching my arm, but tested again and found 90ish VAC on the front speakers of the laptop..................again gone when unplugged.

Any ideas?

 

[gunner]

computers are notorious for earth leakage

 

[desertbootz]

What type of earthing system is being used?

What frequency is the AC.

Is yr insurance up to date?

 

[Graeme Harrold]

Yes I know computers are prone to earth leakage, but I would describe this as a hemorage.

Both premises have TNCS supplies and are wired fuses, no RCD's
didnt check frequency as the PAT machine dosent have the facility to test (only shows supply details), will check on my own printer ater
Yes my insurance is up to date

Its just a bit mad that a printer can cause so much leakage through the printer cable, lot to be said for wireless connections

 

[desertbootz]

If it were a haemorrhage you wouldn't be here :O)

Fluke 6500 should be able to measure touch current. If it's greater than 0.25mA it's a fail.

I may be misrepresenting this but Touch Voltage shouldn't excede 50V either.

I'd say you've probably got a fail there no matter how you look at it. Likely candidates? Breakdown in the PSU of of smothing or EMC filters?

 

[Graeme Harrold]

If it were a haemorrhage you wouldn't be here :O)

Fluke 6500 should be able to measure touch current. If it's greater than 0.25mA it's a fail.

I may be misrepresenting this but Touch Voltage shouldn't excede 50V either.

I'd say you've probably got a fail there no matter how you look at it. Likely candidates? Breakdown in the PSU of of smothing or EMC filters?

Trouble is, both items pass individually, no problem end of job. This fault was kind of highlighted by my "laziness" in not disconnecting all of the cables, therefore unlikely that someone else would have come across the same.

It was the 50V (safe) limit that concerned me too, will go and plug in my printer later and take some more readings...............TBC

 

[zupos40]

Trouble is, both items pass individually, no problem end of job. This fault was kind of highlighted by my "laziness" in not disconnecting all of the cables, therefore unlikely that someone else would have come across the same.

It was the 50V (safe) limit that concerned me too, will go and plug in my printer later and take some more readings...............TBC

Graeme this problems been around since 1990, when electricity of work regs came into force I got a great job testing the proto type seward Pat testers and this was a proble than, keep occuring on IT equipment when two or more item were plugged together.

After extensive investigation, they deemed it to be as a result of how the item talked to each other and that as long as each item was tested separately it was not a problem (yes it was refered back to IEE and electronic experts, I went to brimingham.

May I ask why were you testing the computer in the first, generally a through inspection is sufficient, computors are considered low risk item.

 

[Graeme Harrold]

Graeme this problems been around since 1990, when electricity of work regs came into force I got a great job testing the proto type seward Pat testers and this was a proble than, keep occuring on IT equipment when two or more item were plugged together.

After extensive investigation, they deemed it to be as a result of how the item talked to each other and that as long as each item was tested separately it was not a problem (yes it was refered back to IEE and electronic experts, I went to brimingham.

May I ask why were you testing the computer in the first, generally a through inspection is sufficient, computors are considered low risk item.

These were 4 year old desktops used daily in an accountants office 2 of which actually failed the earth bond test with no connection present, plus 7 IEC leads failed on high resistance. Customer had been having them inspected annualy, but I have dropped this to 4 years in line with the Guidance Notes. I know IT is low risk, but with older fixed wiring (no RCD protection) its prudent to make sure the end connected items are as safe as possible.

Seems more and more places are using cheap import leads with poorer quality conductors

 

[zupos40]

These were 4 year old desktops used daily in an accountants office 2 of which actually failed the earth bond test with no connection present, plus 7 IEC leads failed on high resistance. Customer had been having them inspected annualy, but I have dropped this to 4 years in line with the Guidance Notes. I know IT is low risk, but with older fixed wiring (no RCD protection) its prudent to make sure the end connected items are as safe as possible.

Seems more and more places are using cheap import leads with poorer quality conductors

Yes I would agree with you about the leads should be tested regularlyand that there seems to be a porblem with some IEC leads, I even had 2 cross wired recently (incorrect polarity).

I am now asked to cable tie the IEC lead to the computer once I have tested them and they have passed, I do so with a sticky pad and loose tie.

 

[Darkwood]

Note! When converting A.C. to D.C. in say a computer, printer etc to run the pcb's filters are used which effectively dump any unwanted noise to earth this can be done to suppress radio interference or to smooth out the waveform to name a few reasons, so these appliances are designed to have a 'hi earth current' so if you leave items cabled together by their data wires the screening will effectively keep you linked to the noise.
This is the reason why the regs introduced the strict earthing arrangements for circuits supplying items of hi earth currents.

 

[Liberator]

Yes I would agree with you about the leads should be tested regularlyand that there seems to be a porblem with some IEC leads, I even had 2 cross wired recently (incorrect polarity).

I've had this a couple of times.....

I have actually ripped open the plastic bag of a brand new IEC lead and found incorrect polarity.....