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

So, what's the answer ... well, again I said this earlier - this type of appliance has a plastic shroud over its exposed-conductive-parts, and someone who is competent to service and check that appliance will remove the cover and perform the test the way the manufacturer intended.


In some kit there may not be screws - it may be glued shut, and then it is likely the manufacturer intends it not to need testing ever again once shipped, as even if the earth continuity fails, it cannot fail in a dangerous way that exposes live parts - in which case the required action is an inspection of the outer containment integrity.

What constitutes a "safe" design in the commercial world need not be quite the 'safe' some folk like to imagine - for example the fuse inside a sealed case may be a  kind that explodes firing shards of glass everywhere under certain fault conditions, but so long as the power is disconnected, and so long as  the case can contain those sharp bits and the force of the explosion, then that is perfectly OK, although the use of that same fuse in a case that may be open to the user is utterly unacceptable.

This is part of the (in my view rather thin) argument for not allowing DIN rail parts from some makers inside enclosures from another.

A device that passed the singed cloth test  in one box, may not pass in another. (I kid you not, a special test cloth is put over the MCB or whatever in it's box and subjected to the worst case fault - if  burning bits of plastic and jets of vaporised metal do not emerge and burn the cloth before the thing goes open circuit, then that's a pass..) I suspect this is used as a bit of an excuse, as in reality the containment can be made more than adequate.

As a comparison, for 'really big' gear containment, then a lot of effort goes into directing any blast in the right direction, so cabinets have flaps that allow the metal to bulge, buildings may be designed with one wall that blows out (with "tear here" weakness features built in ) or a substation roof that lifts, to reduce the risk of an uncontrolled structural failure. That 'keep clear' that looks like a parking space you always wondered about maybe for a reason...

regards Mike.

So, what's the answer ... well, again I said this earlier - this type of appliance has a plastic shroud over its exposed-conductive-parts, and someone who is competent to service and check that appliance will remove the cover and perform the test the way the manufacturer intended.


In some kit there may not be screws - it may be glued shut, and then it is likely the manufacturer intends it not to need testing ever again once shipped, as even if the earth continuity fails, it cannot fail in a dangerous way that exposes live parts - in which case the required action is an inspection of the outer containment integrity.

What constitutes a "safe" design in the commercial world need not be quite the 'safe' some folk like to imagine - for example the fuse inside a sealed case may be a  kind that explodes firing shards of glass everywhere under certain fault conditions, but so long as the power is disconnected, and so long as  the case can contain those sharp bits and the force of the explosion, then that is perfectly OK, although the use of that same fuse in a case that may be open to the user is utterly unacceptable.

This is part of the (in my view rather thin) argument for not allowing DIN rail parts from some makers inside enclosures from another.

A device that passed the singed cloth test  in one box, may not pass in another. (I kid you not, a special test cloth is put over the MCB or whatever in it's box and subjected to the worst case fault - if  burning bits of plastic and jets of vaporised metal do not emerge and burn the cloth before the thing goes open circuit, then that's a pass..) I suspect this is used as a bit of an excuse, as in reality the containment can be made more than adequate.

As a comparison, for 'really big' gear containment, then a lot of effort goes into directing any blast in the right direction, so cabinets have flaps that allow the metal to bulge, buildings may be designed with one wall that blows out (with "tear here" weakness features built in ) or a substation roof that lifts, to reduce the risk of an uncontrolled structural failure. That 'keep clear' that looks like a parking space you always wondered about maybe for a reason...

regards Mike.