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 Post subject: When is a pass a pass
PostPosted: Fri Jul 04, 2014 9:44 am 
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Have been testing equipment at a youth camp and found unacceptably high earth continuity on a number of stage lights. (Simple PARCan type as typically used by many travelling discos). Failures were recorded because no exposed metalwork would return a low enough reading. Now I could have opened each of the units and 'forced' a pass by clamping onto the internal earth bond, but this would then effectively have only tested the supply lead - the sort of thing we have all heard of when some companies only test the IEC lead in fear of frying IT equipment). The problem appears to be that the device shell is in two 'halves' one hinged to the other. There is clearly high resistance (approx 3 ohms) across the hinge and my recommendation was that a supplementary bond be fitted across the hinge from the incoming earth. This to my mind is a design flaw as all the units failed in the same way but there was no manufacturers name, model, serial number etc so I can only assume they were made somewhere far away !!!!

What is the general view on this? Should I have just forced the pass or would most of you, like me, have failed all the units. As you can appreciate the customer was not best pleased - even though the fix will probably be straightforward and inexpensive.

I would appreciate your views.


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PostPosted: Fri Jul 04, 2014 1:06 pm 
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Hi Andy

I'm not sure if you are a facebook user, however there is a lively Pat Testing group on facebook where many of the lads and lasses have experience in theatre and DJ cable issues. It might be worth posing the same question there. Be aware that some dicussions can get very lively with people expressing very forthright views, however it may give some different perspectives on the issue you have.

https://www.facebook.com/groups/PatTestingNetwork/

Regards, Richard


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PostPosted: Fri Jul 04, 2014 4:38 pm 
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Location: Leeton, NSW Australia
Hi AndyM,

Not sure where you reside ie UK, Australia or New Zealand

In reading your posting it seems that you have experienced the testing of a "Totally Earth Encapsulated" unit now described/included in Clause 2.3.3.9 of the 2010 version of the Australian/New Zealand Standard-3760, covering PAT testing, described as Testing of Class 1 equipment that is totally encapsulated

This Clause covers what I read as your problem ie knowing that the unit is Class I but cannot get an earth pass result.

The way I test and the method described in the document is to:-
1. Carry out a visual inspection test.
2. Perform a single insulation test. Manually record the result in your Diary.
3. Perform a Leakage test. Manually record the result in your diary.
4. If the unit passes the visual test, print/create a tag just for the visual. If the unit failed the visual then you would fail the unit.
5. After you download the results from your tester into SP the result would/should only show a visual result.
6. Recreate/duplicate the asset/item tested by using the Manual Entry facility and then enter the results you recorded in your diary and don't forget to include the visual result as well.
7. Save the result whereby you will now have a duplicate asset.
8. Manually delete the original downloaded test result.

In relation to what you are suggesting of bridging the unit I would be extremely reluctant to do so as you may create an electrical problem rather than fix the problem.

If you live in the UK contact the staff at SP as I am 99.999999% sure they have a copy of the referenced document and they may be able to show you the relevant Clause otherwise send me, through a private message, your contact details.

Hope this helps.

Glenn


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PostPosted: Sun Jul 06, 2014 8:04 am 
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Hi Glenfer,

Thanks for your post...I am based in the UK so am reluctant in this instance to follow guidance provided in your quoted publication. So far as the equipment tested is concerned, in its crudest form, it is little more than a metal box with a bulb in it, so would certainly not fall into the totally enclosed/encapsulated category. The only external 'insulation' is a very thin layer of black paint or lacquer. As a result, where this is scuffed, and also on unpainted fixings and mounting bolts, there are obvious instances of exposed conductive parts and it is on these that I was unable to obtain the required resistance readings. as a qualified electrical engineer I have no qualms with my recommendation of a supplementary earth bond as this is not bridging anything that would compromise electrical safety. By straddling the rather crude hinge it would simply bring both halves of the shell to the same earth point.

Thanks again for your detailed response. Out of general interest I would still be interested in reading the Australian/New Zealand code.


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PostPosted: Sun Jul 06, 2014 10:04 pm 
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AndyM wrote:
The problem appears to be that the device shell is in two 'halves' one hinged to the other. There is clearly high resistance (approx 3 ohms) across the hinge and my recommendation was that a supplementary bond be fitted across the hinge from the incoming earth. This to my mind is a design flaw as all the units failed in the same way but there was no manufacturers name, model, serial number etc so I can only assume they were made somewhere far away !!!!


Andy, are you completely sure that those PAR cans don't match the fourth example of Class I construction as detailed in the IET Code of Practice (4th ed)?

Quote:
Page 74; section 11.1.4
Class I construction incorporating unearthed metal separated from live parts by basic insulation and earthed metal


It even goes as far as to state on page 73: "In Figure 11.4, the unearthed metal may be in casual or fortuitous contact with the earthed metal. A continuity test made to this 'unearthed' metal may give misleading test results."

Having known and tested similar PAR luminaires by a number of manufacturers, that is definitely how many have been constructed.
The only real way to check if that is the case is to speak to the manufacturer, which unfortunately doesn't look like an option for you. :(

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C&G 2377-01 & -02


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PostPosted: Sun Jul 06, 2014 11:04 pm 
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Thanks Grizzly, You may have a point re the IET CoP however why would a supplementary bond be detrimental to safety? I have had experience in the past in the use of stage lighting lanterns and remember a number of well established UK manufacturers such as Strand Electric and CCT employing supplementary bonds between separate metallic parts of the same luminaire. How have you approached the testing of the PAR cans that you have come across, and have these also shown similar characteristic to those I have recently tested? (approx. 3.5 ohms in the worst case).


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PostPosted: Mon Jul 07, 2014 9:31 am 
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Personally, I can't see a safety problem at all with adding the additional bond.
My point is that it might not be required in the first place, if you determine that the construction is along the lines of 11.1.4, whereby that particular piece of metalwork cannot be exposed to live parts under fault conditions, and so doesn't require earthing.
It may be that the additional expense and work to fit those bonds doesn't provide any increased safety, so you'd have to decide if it's worth it.

_________________
C&G 2377-01 & -02


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PostPosted: Sun Jul 13, 2014 3:21 am 
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Location: Leeton, NSW Australia
Hi AndyM and Grizzly,

Having now read your additional comments following my comments of 6 July, 2014, it appears that your specific code of reference may not use the same terminology as the Aus/NZ Standard but has the same meaning, description and or definition of a "Totally Earth Encapsulated" unit.

The Staff at SP have a copy of the "Downunder" document. The "TEEU" definition was introduced as a specific clause in the 2010 version of the Aus/NZ Standard.

Cheers

Glenn


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PostPosted: Mon Jul 14, 2014 11:11 am 
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Hi glenfer,

I've had a quick look at AS/NZS 3760:2010 (one can find these things if one searches for the right things :wink: ), and I don't think that the definition it gives of 'totally encapsulated' (page 23) is quite the same as the section I quoted from the IET Code of Practice.
They are not totally encapsulated, as earthed metal is easily accessible.
This is what they are getting at, albeit captured from the 3rd edition (we are on edition 4 now), which I think matches the situation with these parcans.


Attachments:
File comment: IET Code of Practice 11.1.4
11.1.4.jpg
11.1.4.jpg [ 45.71 KiB | Viewed 2336 times ]

_________________
C&G 2377-01 & -02
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PostPosted: Mon Jul 14, 2014 12:15 pm 
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Location: Leeton, NSW Australia
Hi Grizzly,

Thank you for your comment.

Regards

Glenn


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PostPosted: Thu Aug 14, 2014 4:08 pm 
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Joined: Sat Mar 15, 2014 1:07 am
Posts: 25
Parcans should be fitted with a bare wire bond between the two halves. You mention a hinge, which I've rarely seen, usually the rear shell comes completely away. The way to rotate the oval beam of light from the can is to stick your hand inside, and rotate the holder! Therefore, modern Parcans should also be fitted with "ParSafe" lamp holders, which are Class 2. (cue discussion on if the earth should now be there at all.) Some have a knob on the outside for this instead of the ParSafe.
I attach the test probe to the bolt holding the yoke to the Parcan, and rarely find a failure.
Other issue is that a large Parcan (PAR64 - diameter of the lamp in 1/8"!) is more than likely 1kW, so generates lots of heat in use. I've had more issues with the cable gland melting than the earth bond failing.


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