PAT testing LED

[grizzly]

And my point:

 

Finally in some electrical equipment components connected to the live/neutral conductors for EMC filtering or surge protection can significantly influence the measurement, indicating an erroneous failure of the test.

.... snip ....

 

Reducing the test voltage to 250V, as now officially included in the IEE Code of Practice, overcomes the problem of surge protection and in reality was introduced as an option in some PAT testers some time ago at the request of end users testing multiway adapters or extension leads as these often have surge protection.

 

Surge protection devices are designed to suppress large voltages, typically those above 300V.

 

As a result, the 500V test will trigger the surge protection whereas a 250V test will not.

[dbuckley]

1) Any kit being sold must be CE marked.

2) To be CE marked it must conform to standards.

3) The standard in this case is likely to be EN60065.

4) EN60065 calls for routine testing during manufacture which comprises...

a) a 10A Earth Bond test

b) a 2kV flash test for Class 1, 3.5kV for Class 2.

 

This group of standads cover design and construction of stuff, and what EN60950 says (and I'll assume EN60065) is that before such a test you may disconnect stuff that is not involved in the insulation test, and this would include MOVs.

 

Now, for In-Service Testing you're not required to do a flash test but there is no reason kit shouldn't pass a 500v DC leakage test.

 

In New Zealand, in-service testing is covered by AS/NZS 3750:2010, which doesn't appear to have a more global reference, and it specifically says, E2.2(b):

 

A nominal measuring voltage of 500V DC. (To avoid equipment apparently failing the test, 250VDC may be used for equipment containing surge protection devices such as MOVs/EMI filtering, that bridge the insulation being tested)

 

My bold. The standards writers clearly understand that a MOV conducting at 500V will invalidate the test, and lead to apparent failure, that is testing showing a failure when the equipment is in fact sound.