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Topic Title: PAT Testing Multiple Rack Mounted Units
Topic Summary: Paradime
Created On: 09 January 2019 09:49 PM
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 09 January 2019 09:49 PM
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jd7688

Posts: 2
Joined: 09 January 2019

Hi
I am a technician working mainly with lighting, sound and av equipment for the entertainments industry.

I have recently come across a unit which I am struggling to design a testing scheme for and am looking for any input I can gain.
The unit is a rack mounted touring dimmer unit, with 6 6 channel rack mount dimmers, a patch panel and a socapex output panel. Additional the unit provides multiple non dim outputs. The power input is a 3 phase 125a ceeform connector.

My concern is while performing an earth leakage test, the unit currently fails as a whole on the 0.75ma limit, however it passes the 3.5ma limit of a static appliance. Each individual dimming unit will also pass the 0.75ma limit. The unit is currently not in use as a fail, however I am unsure if testing it as a class 1 on portable appliance is fair as the unit is over the 18kg suggested weight for transportable appliances (by some pat tester providers) and forgetting its flight case mount is as easy to move as a fridge. however it is a touring unit and designed to move on a regular basis.

Despite it being so heavy and so big, should I test the unit as a portable appliance, or is it fair to treat it as a static appliance?

can I perform the earth leakage on each individual unit within the main unit, or should I treat it as one whole thing?

Thankyou in advance for any help you may be able to give!
 10 January 2019 09:50 AM
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davezawadi

Posts: 4259
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This equipment is clearly not a portable appliance! PAT testing such an item is foolish to say the least, it is electrical distribution equipment, and it takes a significant level of power input, probably at least 50kW! PAT testing is aimed at power using equipment, at the end of a circuit where earth continuity may be suspect, and leakage should be controlled. The dimmers may well have a leakage (actually switching transients current) of many times your PAT limit, but this is in no way a problem and to be expected.

Routine installation test will include a Zs check after connecting up, which is quite sufficient for safety. See BS7909 for more information.

-------------------------
David
BSc CEng MIET
 10 January 2019 12:20 PM
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broadgage

Posts: 3170
Joined: 07 August 2007

PAT testing by means of a machine with pre-set pass/fail thresholds is primarily intended for relatively small and self contained portable or transportable appliances that are connected via either 13 amp plugs or other connectors of similar capacity.

The equipment rack in question is clearly not part of a fixed installation as it is routinely transported.
The size, electrical loading and number of sub-assemblies also mean that testing as a "normal" portable appliance is not applicable.

Therefore some engineering judgement needs to be applied as to what tests are applicable.
I would be inclined to test it as though it was a fixed installation, despite the portability.

Test and inspect for
Earthing of all parts that should be
Live parts protected from touch.
Polarity correct.
Correctly sized OCPDs.
Ramp test of any built in RCDs or RCBOs.
Insulation resistance, between earth and all live conductors connected together.
General fitness for use in the reasonably expected conditions that it is likely to be used in.
In general, "pretend" for testing purposes that it is an installation, and test it thus, completing a form of test results based upon that used for a fixed installation.

Any readily removable sub-assemblies that might reasonably BE removed for use elsewhere should be PAT tested separately.
 10 January 2019 03:22 PM
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mapj1

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As a practical matter for thngs I design like that, we don't consider a 100A 25mmsq 'flex' to be anything as likely to lose the CPC as say the cable on a kettle or a sandwich toaster, and at least for stuff we build we allow up to 10mA leakage, and provide lugs so the nervous can add supplimentary bonding as required.


-------------------------
regards Mike
 22 January 2019 08:53 PM
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jd7688

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Joined: 09 January 2019

Thank you, all much appreciated.

Would the appliance not come under a portable appliance test as it has a plug (plugs into a socket) and it is portable, it does commonly move, or is that voided by the fact it is basically a power distribution unit?

I am using a data base driven PAT tester so the test sequence can be defined by the user.
As far as electrical tests if I check for earth bonding (.10ohms to all outputs and case), insulation resistance (=>2Mohms) and earth leakage (3.5ma) with the Pat tester, would these sound fair pass marks? Coupled with the suggested visual, polarity and functional test of the unit.
 22 January 2019 10:18 PM
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sparkingchip

Posts: 11682
Joined: 18 January 2003

Have you actually made up a fly lead with a 13-amp plug and a 125-amp three phase trailing socket to be able to plug the equipment into a PAT tester?

Andy B.
 22 January 2019 10:20 PM
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IronFreely

Posts: 445
Joined: 06 November 2014

Hi, this is an area of my own personal interest/experience as many moons ago I was but a humble theatre technical manager...

First I would not class a dimming rack of your description as a portable appliance, but that doesn't mean it shouldn't be subject to periodic inspections and testing as I will detail below.

Don't worry about the leakage, just whack a warning notice on it...

Essentially a dimming rack is a consumer unit with some brains so you should carry out a similar set of inspections and tests, such as, the outer casing should be sealed and un-damaged (IP rating), all leads and accessories should be free from defects with no basic insulation showing, check continuity between exsposed conductive parts and earth pin of supply ceeform, continuity between Earth pin on supply ceeform and earth pin on output channels, check all connections within are sound with no signs of over heating or arching (especially connections to any MCBs or RCDs) in my expirience most touring racks have both, unless you're dealing with a little alpha pack or something . Check MCBs are correct rating for relevant outputs (64A, 32A, or 16A for relevant sized commando/ceeform sockets, 25A or less for socapex, 10A for IEC or square pin). Check MCBs and RCDs genuinely isolate relevant output channels. I might class a dimming rack as senistive so if I did an insulation resistance test I'd do it at 250v but it might come up a bit squiffy especially testing between L&N. Carry out an RCD trip time test and an RCD trip current test (Ramp). I'm not sure what kind of rack it is but if it has manual faders then a functional test is in order.

Or and this is a big "or"...
Or simply contact the manufacturer and ask them for guidance on periodic testing and inspecting requirements as it is most certainly what I would class as a specialist piece of equipment that is only used under the supervision of specialist stage engineers such as you and me.
Check the manual if you have it...

I've got a fair few friends who do hire and supply of such things so I'd be happy to put you in touch if you want to message me your contact details.

Always remember that if any of the magic smoke comes out you probably can't fix it.
 22 January 2019 11:43 PM
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broadgage

Posts: 3170
Joined: 07 August 2007

Originally posted by: jd7688

Thank you, all much appreciated.
Would the appliance not come under a portable appliance test as it has a plug (plugs into a socket) and it is portable, it does commonly move, or is that voided by the fact it is basically a power distribution unit?
I am using a data base driven PAT tester so the test sequence can be defined by the user.
As far as electrical tests if I check for earth bonding (.10ohms to all outputs and case), insulation resistance (=>2Mohms) and earth leakage (3.5ma) with the Pat tester, would these sound fair pass marks? Coupled with the suggested visual, polarity and functional test of the unit.


It is undeniably portable, and yes it is an appliance, albeit a large and complex one.
It therefore requires testing so as to ensure safety in use.
However the size and complexity means that the normal pass/fail limits intended for kettles and toasters are not applicable.

3.5ma earth leakage might well be exceeded despite the unit being in good condition.
Likewise 2 megohms insulation resistance may be a bit optimistic.

To take an extreme but illustrative example, consider a large portacabin used as a site office, and fitted with 10 PCs, and numerous faxes, routers, printers and other IT stuff, together with a fridge, kettle, toaster, and small cooker.
A portacabin is somewhat portable, but would you expect the total earth leakage to be under 3.5ma ?
 23 January 2019 08:26 AM
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sparkingchip

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Originally posted by: sparkingchip

Have you actually made up a fly lead with a 13-amp plug and a 125-amp three phase trailing socket to be able to plug the equipment into a PAT tester?



Andy B.


I was thinking bigger than a portacabin, more like a terrace of six houses.

Andy B.
 23 January 2019 09:01 AM
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sparkingchip

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For several years I have inspected and tested some temporary distribution boards for an event company, although they are very basic I still end up using installation testers alongside a PAT tester to complete the testing.

Andy B.
 23 January 2019 09:11 AM
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mapj1

Posts: 12039
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As a rule of thumb, you may expect leakage to scale with current demand, and not be more than about 1/1000 - so never more than 30mA on a 30A circuit, 100mA on a 100A circuit etc. It may well be a lot less, nearer 1/10000, but as noted above, the total load you are talking about here is comparable to a few houses worth.
If you can, record the measured values , because noting changes is more use than the absolute value in deciding if something is deteriorating, and in any case, the main concerns with anything theatrical is more likely to be visual inspection for signs of rough treatment and damage than electrical performance per-se.

Actually if you need an 'is it safe test' when bounced about and moved to a new location, then some sort of earth loop test is more suitable.

-------------------------
regards Mike
 23 January 2019 10:59 AM
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davezawadi

Posts: 4259
Joined: 26 June 2002

I think you have not quite taken on my comments about BS7909. It is the "bible" for these kinds of equipment, not PAT or BS7671. PAT earth leakage tests are fine for domestic appliances but not relevant to equipment like this. You PAT test cables and single lighting items, backline and small appliances but it is not suitable in any way for dimmers, or large PA systems which take 10s or 100s of kW. Earth leakage on these items with no load may well pass, but when working may be much higher, however this is in no way dangerous. The important tests are only insulation to metalwork from supplies, earth continuity and resistance, and inspection for mechanical damage of everything. BS7909 then specifies testing once the whole installation is wired up, which is similar to a BS7671 new installation. This step is often ignored by some operators, but is the only way to ensure that there has been no problems during transport and installation. It need not take long, but checking earthing of major items and possible exposed or extraneous parts is essential for safety. You then issue the test certificate in the usual way. No certificate and an accident is the way to have the HSE all over the technical manager and a likely large fine. Portable is in no way connected to a plug or socket, you will notice that you cannot plug these items into the tester without a special cable, and a 13A plug to a 3 phase group of 400A powercons looks a bit odd, particularly when you try switching on for the load test at 300kW plus!

-------------------------
David
BSc CEng MIET
 23 January 2019 11:50 AM
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sparkingchip

Posts: 11682
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My understanding is that each item of equipment that makes up a temporary installation should arrive on site with PAT having been completed, so that the installation can be assembled without it going bang and the BS7909 installation certificate does not require any insulation test results for the entire installation, as each component part of it has already been PAT off site.

So the designer of the temporary installation needs to consider the cumulative total earth leakage, which will be way in excess of the PAT pass limits for the component parts of the temporary installation.

Andy B.
 23 January 2019 02:37 PM
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Legh

Posts: 4427
Joined: 17 December 2004

Well, at what point do appliances become portable and visa versa?
My experience has shown that electricians doing Inspection and Testing do not test portable appliances, in fact any appliances unless previous arrangments are agreed.
PATesters will only test appliances that can be moved and have a standard BS1363 or BS EN60309-2. That leaves gaps where appliances do not get tested at all. Examples are compressors, stand drills, metal saws, arc welders, grinders, cookers, any applaince that has been hard wired through an Isolator or/and SFCU.
We don't have equipment racks par se but all our theatre lights, mixers, dmx conrollers and Lighting patch panels are checked, the PA system is checked separately by the company who installed it.

It appears to me then, that whatever system is used the equipment must be checked and suitable proof made available through some form certification. It would be the duty holder who would decide which method was appropriate.

Equipment racking that is moved around after each show could be regarded to be portable regardless of an upper weight limit and by others to be movable/fixed/stationary/fitted and the methods of testing maybe changed according to the sensitivities of the instruments being tested.

Legh

-------------------------

http://www.leghrichardson.co.uk

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 23 January 2019 03:23 PM
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AJJewsbury

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Perhaps that why the powers that be prefer the phrase "In-service Inspection and Testing of Electrical Equipment" to "portable appliance testing".
- Andy.
 23 January 2019 04:01 PM
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davezawadi

Posts: 4259
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I have not suggested we don't test anything, but BS7909 is clear on "how to test" temporary installations. I know that all manner of people think that the "tests" are important, but the main priority is to Inspect the items. Pre-testing everything, then driving a lorry over the connectors damaging the earth connection is much more likely than such breaking in normal use. Testing before shipping is only a bit of risk reduction, it is still necessary to ensure that the temporary installation is safe. PAT is not an effective procedure under most useage regimens, although it seems that many think it does something useful, and often yearly. Equipment could thus be faulty for 11+ months before a cable defect is noticed by inspection not the test itself. The important bit is the record of problems over the life and then deciding how often it needs to be checked for reasonable safety.

-------------------------
David
BSc CEng MIET
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