Leakage test fails on PCs

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Leakage test fails on PCs

Postby andriusst » Tue Jan 29, 2013 11:06 am

Hi,

PrimeTest 100 keeps failing PCs and servers on ileak test. For example this particular rack mount server test returned 1.01ma leakage current which is above factory preset "pass" threshold and therefore the result is fail. So I was wondering what is the max acceptable leakage current for personal computers and rack mount servers? Thanks.

regards
Andrius
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Re: Leakage test fails on PCs

Postby Patnik » Tue Jan 29, 2013 11:43 am

I regard rack-mount equipment as 'stationary' so leakage current up to 3.5mA is acceptable. About 1mA is quite normal - many servers have more than 1 'hot swappable' PSU and they may each be over 1mA. I do expect this sort of equipment to be properly supplied from a 16A high integrity supply or similar - I won't pass it if it's supplied via a domestic extension lead if I calculate the leakage current at the extension lead BS1363 plug much exceeds 3.5mA.

Desk top PCs I expect to be under 0.75mA as they tend to get moved about when plugged-in so can be regarded as portable even though they are obviously IT equipment. Many (eg some Apple iMacs) are borderline though so I don't go failing them if I get a reading of 0.85mA or whatever as that's what the manufacturer designed.
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Re: Leakage test fails on PCs

Postby safe + sound » Tue Jan 29, 2013 5:39 pm

An interesting post Patnik. I agree rack-mount IT equipment is 'stationary' but consider a desk-top PC to be movable equipment and therefore fall under Other Class I Equipment in table 15.3, page 96 in the CoP with a 3.5mA maximum.
What is your concern if the total leakage on a BS1363 extension lead exceeds 3.5mA?
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Re: Leakage test fails on PCs

Postby Patnik » Wed Jan 30, 2013 11:07 am

Good questions safe + sound,

I'd agree that desk top PCs could be classed as movable equipment in many situations but where I work there is great aversion to shutting them down so it is quite common for a user to move a PC from desk to desk, or dump it on the floor to clear some room, without unplugging it. I think this is bad practice but as neither the IT staff or I can control it I use the preset portable equipment test with the 0.75mA limit. With a liberal interpretation of this limit I've only ever ended up failing very old or genuinely faulty PCs so no ones got upset.

The earthing facility of a BS1363 plug is only designed to be safe for a maximum of 3.5mA earth leakage which is why the CoP gives this as a maximum and asks that equipment exceeding this comply with the 'High protective conductor current' provisions in Section 15.11 (or would do if they bothered to proof read it properly ;) ). The risk of the inadequate earth, in particular the single screw terminal in the plug, failing and exposing the user to touch current in excess of 3.5mA is just as real whether the plug be connected to a single high leakage appliance or several lower leakage appliances whose design leakage currents add up to more than 3.5mA.

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Re: Leakage test fails on PCs

Postby safe + sound » Wed Jan 30, 2013 12:54 pm

Thanks Nik, though I don’t entirely agree with your reasoning on the 3.5mA maximum for a BS1363 extension lead, you are applying a ‘safer’ limit that works in your particular circumstances.

[The earthing facility of a BS1363 plug is only designed to be safe for a maximum of 3.5mA earth leakage which is why the CoP gives this as a maximum and asks that equipment exceeding this comply with the 'High protective conductor current' provisions in Section 15.11 (or would do if they bothered to proof read it properly ]

The earth connection on a BS 1363 plug will have a much higher current rating to handle earth fault conditions, albeit for a limited time.

[The risk of the inadequate earth, in particular the single screw terminal in the plug, failing and exposing the user to touch current in excess of 3.5mA is just as real whether the plug be connected to a single high leakage appliance or several lower leakage appliances whose design leakage currents add up to more than 3.5mA.]

Equipment with high protective conductor current permanently connected to the fixed installation via a fuse connection unit would have its protective conductor terminated with a single terminal screw.
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Re: Leakage test fails on PCs

Postby Patnik » Wed Jan 30, 2013 1:59 pm

Yes you're right, there are various examples of equipment with leakage current >3.5mA but <10mA having the earth secured by only one screw. I mention that as it's the only common earth point I've found to have failed on an extension lead to date.

I don't have a copy of BS1363 so maybe wrong but I've always understood that the 3.5mA earth leakage is the design limit of the plug, both the CoP and BS7671 make it clear that equipment with a protective conductor current designed to exceed 3.5mA should:

1. be permanently wired to the fixed installation or be supplied by a BS EN 60309 industrial plug
2. have internal protective conductors of not less than 1mm
3. have a 'high protective conductor current' warning label as specified

I don't see that this excludes equipment fed from a single source via an extension lead just because the individual units leak less than 3.5mA, it would make a nonsense of the requirement.

Leads fitting this criteria with BS1363 outlets are readily available for IT applications. The problem tends to be that users either don't recognize the problem or don't want the expense of installing the appropriate sockets. I've seen unbonded IT racks with total earth leakage of over 15mA supplied via piggy-backed BS1363 extension leads before - a failure of the common earth point would result in all the metalwork becoming dangerous.

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Re: Leakage test fails on PCs

Postby andriusst » Tue Feb 19, 2013 11:07 am

hi thanks for your replies. I was going to ask few more questions but you have discussed them already. Thanks again.
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Re: Leakage test fails on PCs

Postby fccvs4 » Tue Jan 28, 2014 2:35 pm

A brand new primetest 100 has failed every desktop computer we have. This includes a brand new dell taken out of it's box for comparison. They all fail on the Ileak test with readings between 0.77 up to 1.1

Other replies indicate that people are using their judgement and passing when the readings are in this range, this would imply that there is a higher acceptable level than the factory set 0.75.

The seaward guide supplied with the equipment says this:-

portable or hand held class one equipment = 0.75
class one heating appliances = 0.75 or 0.75 per kW whichever is greater to a max of 5.0
All other class one equipment = 3.5

Personally, I would not call a desktop computer portable. Yes, you can move it from desk to desk, but not without disconnecting everything first. Generally, it will stay in one place as long as a fixed server would.

This might mean that some people would pass desktop computers up to 3.5 mA
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Re: Leakage test fails on PCs

Postby Grizzly » Tue Jan 28, 2014 8:38 pm

The PT100 doesn't do a 'proper' differential leakage test at 230V, but rather a 'substitute' leakage test at 40V.
(see explanation by Seaward's Jim Wallace here: http://www.seaward.co.uk/forum/viewtopic.php?f=3&t=55609).

I personally wouldn't be bothering with any sort of leakage test on computer equipment, if the earth bond and IR tests are passed OK.
C&G 2377 -01 & -02
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Re: Leakage test fails on PCs

Postby Stephen Armstrong » Wed Feb 19, 2014 5:20 pm

Thank you for your enquiry

Substitute leakage is measured between both line and neutral and the protective earth conductor. It is similar to an insulation resistance measurement except that a test voltage of 40V/50Hz is used rather than 500V DC. The measured current is then automatically scaled by the tester to show the leakage that would present at mains voltage (i.e. scaled by a factor of 6). If the appliance under test has filter components between both line-earth and neutral earth (as appears to be the case with the washing machine) the substitute leakage method will measure both leakage current. The IET Code of Practise includes the substitute leakage method but does not have limit values that take into account the additional leakage path between neutral-earth.

Differential leakage is measured at the normal supply voltage with a normal supply connection i.e. it is a true indication of the leakage under normal operating conditions and is therefore a much more robust measurement. If the differential leakage measurement value is less than the limits specified by the IET CoP then the appliance is OK.

In addition, according to ch15.5 (of the 4th Code of Practice), the insulation test should be applied at 500Vdc (which it is with a PT 100) and according to ch15.6 the protective conductor/touch current measurement is an alternative or complementary test to be carried out if the insulation test in ch15.5 can’t be performed or gives suspect results.

Kind regards
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