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PAT Testing Speakers

PostPosted: Mon Jun 25, 2012 8:14 pm
by grantsonuk
He guys

Im trying to test a set of powered speakers
1 8" monitor speaker which passed after eventually finding an earthed screw

and 2 12" main speakers, I am unable to get a good earth on and of the screws on the casing or the terminals

Can anyone provide any advice on this one?

Thanks
Grant

Re: PAT Testing Speakers

PostPosted: Mon Jun 25, 2012 9:03 pm
by Alan Freeman
Grant

I have tried some of these and had some success using the screen of the signal leads - but even these are not always earthed to the power earth.

As with any class 1 item, if you can't find an earth, you might have to test as Class 1 no earth..

Re: PAT Testing Speakers

PostPosted: Mon Jun 25, 2012 9:34 pm
by grantsonuk
Thanks Alan

I thought about that but some of the screws on the case are just over the limit and some have massive resistance
One came within 0.01 when set limit calc to account for the iec lead and tested the same screw again the reading was off the scale.

I have to say im massively confused

Re: PAT Testing Speakers

PostPosted: Mon Jun 25, 2012 10:34 pm
by Alan Freeman
Are you saying that the one screw was 0.01 outside the limit of 0.1 ohm, but when you re-tested with limit calc it was >19.99.

I do not know why the second reading was off the scale, but I suppose you could accept the first reeding and change the result from fail to pass with a reading of 0.11.

I realise this is not a stable result, but you have physically seen a result which was in range, so if you had the limit set, you would not have re-checked it!!

Re: PAT Testing Speakers

PostPosted: Tue Jun 26, 2012 6:39 am
by Grizzly
Don't forget parts 11.1.3 and 11.1.4 of the Code of Practice.
These screws may only be in 'casual or fortuitous' contact with the actual earthed parts, and so could give misleading results.

Re: PAT Testing Speakers

PostPosted: Tue Jun 26, 2012 3:02 pm
by grantsonuk
Thanks Grizzly

Im about to go and try again with these

It was mainly that the RCA terminal were giving huge reading on both speakers I thought that they should give a clear reading

on the plus side the IEC leads are all clear lol

Re: PAT Testing Speakers

PostPosted: Tue Jun 26, 2012 5:01 pm
by grantsonuk
Done :)

after trying every damn screw on the case and getting readings all over the place I decided to try the large block of anodised aluminium cooling fins which id been ignoring figuring there was snowballs chance and hey presto all passed

Im wondering if there is some kind of hypersensative surge protection in there as there were some screws that gave low readings that then spiked way up dring the test

Re: PAT Testing Speakers

PostPosted: Tue Jun 26, 2012 7:13 pm
by Alan Freeman
Had you mentioned the heatsink (cooling fins) on the back, I would have directed you there straight away. They are part of the active circuitry, but must be at earth potential - so will have a direct earth connection. Solid every time.