Earth Bond Tests on laptops/TV/printers etc

[PhilCook]

I've seen the posts dealing with this, but none seem to state a solution I can comprehend I therefore submit the following scenario:

A three pin IEC lead connect to an adaptor that outputs to an 0.5m 18AWG four pin DC connector that plugs into a TV.

Transformer outputs 12V 4A and neither it nor the TV has any symbols.

IEC lead is tested as standard class 1 with an Earth Bond result of 0.05
IEC lead is attached to transformer block and Test Lead attached to pins inside DC connector and Earth Bond test returns 0.32

As there is a return do I assume that the Earth cable is continuous and fail it or do I treat it as low voltage and not test either the transformer or TV beyond visual inspection?

 

[Grizzly01]

The TV would not need an earth bond, insulation or any other 'PAT' test (other than a visual inspection), as it is an extra-low voltage supplied item (< 120V dc).
The power supply, however, is supplied by low voltage (50 - 1000 Vrms), aka 'mains' 230V, so certainly some electrical tests would be appropriate.

A couple of thoughts:

The pass limit for the earth bond test is (0.1 + R) ohms. As you have measured R already (the resistance of the protective conductor of the supply cord) as 0.05 ohms, the pass limit would be 0.15 ohms. So your combined result is still too high...

Not sure what model tester you're using, but it could have one of 2 methods to measure the earth bond resistance:

If it uses the 4-wire method - so the earth bond 3-core lead connects to the tester via a 3-pin plastic XLR-style connector - then the resistance of the test lead is automatically ignored by the test.

If it's just single wire - so connects to the tester via a banana plug or similar - then there should be a way on the tester to null the resistance of the lead. If this is the case, have you checked that the lead is nulled, and not adding unduly to the result?
(I am assuming here that the IEC lead plugs directly into the tester at both ends for the lead test, and doesn't use the test lead & clip.)