Light for understair cupboard

[securespark]

In both cases one disconnects wires in the hope of making it right and powers up. In both cases there is scope to re-energise a dead short.

What I'm saying is that, with the best will in the world without professional test equipment that diyers don't have, there is always an element of what you protest should not happen.

 

[ban-all-sheds]

Good luck testing an unpowered unloaded SMPSU

 

[securespark]

Don't understand. You can just megger L&N to E.

 

[ban-all-sheds]

But that does not really test the functioning of a SMPSU - this is blowing a fuse, not tripping an RCD, so it's a L-N overcurrent problem, not a leakage one.

 

[bernardgreen]

Don't understand. You can just megger L&N to E.

Putting the 500 volts from a megger onto the terminals of an SMPS is likely to do some harm to the device. May not kill it immediately but damage it enough that it fails sooner than it would have done had it not been "meggered"

 

[securespark]

Surely not if you put L&N together then measure between that and earth?

Been doing it all my life and not killed anything!

 

[bernardgreen]

The vunerable components are the capacitors and bleed resistors in the mains input filters. The item still works but is then prone to malfunction if the mains supply is noisy. Audio equipment and communications equipment functions but audio noise levels increase.

 

[securespark]

Sure, but meggering between L/N combined and earth will not damage these components.

 

[bernardgreen]

will not damage these components.

The capacitors that are connected Live~~Earth and Neutral~~Earth are the components at risk of being over volted.

 

[securespark]

That's a new one on me; I thought they were connected across L-N.

 

[ban-all-sheds]

No - that's why people get problems with accumulated leakage from lots of SMPSUs