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

Arran Cameron:

Plastic class 1 devices where the earth conductor of the mains cable is connected to a metal chassis inside, or is used for screening EMI, has to be tested as class 1 rather than class 2 because of the potential for earth leakage current that could trip a RCD.


There was a (at least one) case of a plastic class 1 device in a hospital that would trip a RCD because of a fault resulting in excessive earth leakage current, but it successfully passed the class 2 EST that was being used at the time.

Is that a safety issue? I can, however, see that in hospitals, more attention is absolutely necessary with equipment that may be used in a Group 1 or Group 2 medical location - but I'd expect a greater degree of competence to test and maintain that equipment anyway?


In any case, even testing Class I appliances in that way won't always detect issues that cause RCDs to trip - or even detect all faults.


For example, if you test a washing machine, a faulty component or circuit may not be switched "on" until the door is closed and the interlock connects, and the component is in circuit set by the control board.


 

Arran Cameron:

Plastic class 1 devices where the earth conductor of the mains cable is connected to a metal chassis inside, or is used for screening EMI, has to be tested as class 1 rather than class 2 because of the potential for earth leakage current that could trip a RCD.


There was a (at least one) case of a plastic class 1 device in a hospital that would trip a RCD because of a fault resulting in excessive earth leakage current, but it successfully passed the class 2 EST that was being used at the time.

Is that a safety issue? I can, however, see that in hospitals, more attention is absolutely necessary with equipment that may be used in a Group 1 or Group 2 medical location - but I'd expect a greater degree of competence to test and maintain that equipment anyway?


In any case, even testing Class I appliances in that way won't always detect issues that cause RCDs to trip - or even detect all faults.


For example, if you test a washing machine, a faulty component or circuit may not be switched "on" until the door is closed and the interlock connects, and the component is in circuit set by the control board.