Class 1 Testing with the Primetest 250

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Re: Class 1 Testing with the Primetest 250

Postby agbtester » Wed Apr 06, 2011 9:06 pm

Why does it stop the class 1 test on an appliance due to the earth continuity test being over the limit, but will carry on with a cord test with the same earth bond reading ?

Shorly it should halt both tests if the earth continuity result is over the limit, and wait for user confirmation to carry on with the insulation and leakage tests.

As you say it may be a basic tester with extra features, but I have just purchased this tester to carry out testing on appliances and cords....., and it seems that any equipment I test with a long cord I can not fully test....

I wait on your product managers prompt reply.
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Re: Class 1 Testing with the Primetest 250

Postby Grizzly » Wed Apr 06, 2011 11:37 pm

agbtester wrote:Why does it stop the class 1 test on an appliance due to the earth continuity test being over the limit, but will carry on with a cord test with the same earth bond reading ?


I would say that it's because during the Class I appliance test sequence, in particular the leakage test, the appliance will be energised to 230V ac, so one must be certain that the protective earth is present, and of a low enough resistance to be effective under fault conditions. As the PT250 has already recorded an earth continuity fail (of > 0.2Ω), then as far as it's concerned, it is not safe to proceed with any 'mains powered' tests, and so will not allow it.
A supply cord under test is not subjected to any 'mains powered' tests, and so it must have been considered safer to proceed with the rest of the test sequence.

That's my thinking, anyway.
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Re: Class 1 Testing with the Primetest 250

Postby agbtester » Wed Apr 13, 2011 10:31 pm

Could anyone verify the difference on an insulation test between a class 1 and a class 2 appliance.

I understand a 500v dc voltage is applied between phase / neutral and the earth return path of a class 1 appliance, and between the phase / neutral and the test probe for a class 2 appliance.

Re my query on the issue of testing a class 1 appliance with a long cord with a PT250.... an earth continuity fail result leading to a halt on the test.........and confirmation the test should have been a pass if the cord resistance had been subtracted.

Isn't this the same (insulation) test if you place the probe to an earth point on a class 1 appliance, and apply a class 2 insulation test....to overcome my issue of a halt in the class 1 test procedure.
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Re: Class 1 Testing with the Primetest 250

Postby Grizzly » Thu Apr 14, 2011 3:31 pm

agbtester wrote:Could anyone verify the difference on an insulation test between a class 1 and a class 2 appliance.

I understand a 500v dc voltage is applied between phase / neutral and the earth return path of a class 1 appliance, and between the phase / neutral and the test probe for a class 2 appliance.


Yes, that's exactly right.
It's generally outlined on page 75 of the IEE Code of Practice, and the method will be more specifically described in the instruction manual of your PAT instrument.

Re my query on the issue of testing a class 1 appliance with a long cord with a PT250.... an earth continuity fail result leading to a halt on the test.........and confirmation the test should have been a pass if the cord resistance had been subtracted.

Isn't this the same (insulation) test if you place the probe to an earth point on a class 1 appliance, and apply a class 2 insulation test....to overcome my issue of a halt in the class 1 test procedure.


I can see where you coming from with that.
However... have a look at pages 55 & 56 of the IEE CoP, specifically sections 11.1.3 (Class I construction incorporating unearthed metal separated from live parts by basic and supplementary insulation) and 11.1.4 (Class I construction incorporating unearthed metal separated from live parts by basic insulation and earthed metal).

If you were to unwittingly connect your test probe to one of these unearthed metal parts (if present on the appliance under test), and ran a Class II insulation resistance test, which passed with flying colours, the fact that the metal parts were unearthed could be masking an insulation breakdown on other parts of the appliance, between the live parts and actual earthed metal.
A Class I IR test would not be prone to this potential fault masking.
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Re: Class 1 Testing with the Primetest 250

Postby agbtester » Thu Apr 14, 2011 10:25 pm

Due to the unorthodox IR method, would not multiple class 2 tests be required to overcome the possible issue you have indicated.

It appears that I have made an error on purchasing the PT250, all I required was a simple PAT tester that conducted all tests without any issues, plus without the additional cost for memory.....

Thanks for your assistance on this matter.
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Re: Class 1 Testing with the Primetest 250

Postby Grizzly » Sun Apr 17, 2011 10:15 pm

agbtester wrote:Due to the unorthodox IR method, would not multiple class 2 tests be required to overcome the possible issue you have indicated.


Yeah, that would be a way of getting round it.
I still wouldn't be happy doing it, though.

It appears that I have made an error on purchasing the PT250, all I required was a simple PAT tester that conducted all tests without any issues...


I've always considered fixed-limit testers to be a pain in the rear, and Sod's Law says you'll always come across an appliance that foxes them.
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Re: Class 1 Testing with the Primetest 250

Postby Richard Williams » Mon Apr 18, 2011 11:11 am

Hi

The above is correct from Grizzly. The failure on the Class I Earth Bond test is there to prevent any danger being present if the appliance was energised during the Leakage test. If there is no protective earth and the appliance faults, there could be a fatal risk.

Again, as there is no leakage carried out on extension leads, the tester will allow the rest of the test to be carried out in the event of failure.

The Class II insulation test is in theory the same as long as there is a good earth point to connect to. Grizzly does bring a good point forward to say that even if the metal point wasnt connected to earth you would get a false pass.

We are looking into ways of improving the PT250 to overcome this issue.
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