Class 1 appliance with no exposed metal work to connect test lead too

So, you have a device with mains inside it. It may have a 2 core lead or 3.

The over-arching principle is "double fault to danger" - no single failure of a wire off or a single layer of damaged insulation should put a user at risk.


If there are conductive parts the user may hold these must not be live in operation, or able to become live in a single fault condition.


Therefore exposed parts that are either solidly earthed, or well enough insulated from all 3 cores to hold off mains voltage (so if the earthed bits inside came live from a first fault it would not matter)


So test L+N to CPC - should be high impedance. (no first fault)

test CPC to exposed metal - if connected, impedance must be low enough to clear fuse on first fault.

If not connected, retest at 500V  from CPC to exposed sufraces -  should be no connection, so if later there is a fault that makes the earthed bits inside live, you can be sure it will not reach the user, so you retain double fault to danger.


It is important to recall that this Class 0, 0A ,1,2 3 business  is only  an arbitrary classification that is a convenience for grouping devices whose safety is assured in a particular way, so that the correct tests can be performed in order, and without too much thought.

if you have something that does not  fit the classification, then like the chaps who dreamed it up, you need to think a bit about what you are trying to test and why. (in nature we have the odd platypus..)


Of course any test is a snapshot on the day - if the user drops the thing in the sink or down the stairs and then it is dangerous, then that is their call, the tester is not liable for that.

regards

Mike.

So, you have a device with mains inside it. It may have a 2 core lead or 3.

The over-arching principle is "double fault to danger" - no single failure of a wire off or a single layer of damaged insulation should put a user at risk.


If there are conductive parts the user may hold these must not be live in operation, or able to become live in a single fault condition.


Therefore exposed parts that are either solidly earthed, or well enough insulated from all 3 cores to hold off mains voltage (so if the earthed bits inside came live from a first fault it would not matter)


So test L+N to CPC - should be high impedance. (no first fault)

test CPC to exposed metal - if connected, impedance must be low enough to clear fuse on first fault.

If not connected, retest at 500V  from CPC to exposed sufraces -  should be no connection, so if later there is a fault that makes the earthed bits inside live, you can be sure it will not reach the user, so you retain double fault to danger.


It is important to recall that this Class 0, 0A ,1,2 3 business  is only  an arbitrary classification that is a convenience for grouping devices whose safety is assured in a particular way, so that the correct tests can be performed in order, and without too much thought.

if you have something that does not  fit the classification, then like the chaps who dreamed it up, you need to think a bit about what you are trying to test and why. (in nature we have the odd platypus..)


Of course any test is a snapshot on the day - if the user drops the thing in the sink or down the stairs and then it is dangerous, then that is their call, the tester is not liable for that.

regards

Mike.