Electronics > Beginners

Brymen BM235 10A fuse silently destroyed by a switched off UPS leakage current..

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hgg:
Indeed.
I measure leakage with a clamp meter.

In this case the UPS was off, it could not power on any device, apart from the blinking
led of the Raspberry barely, and I was curious to see why there was 230V between
ground and live and ground and neutral but with no power to turn on even the Raspberry.

But in order for the fuse to blow there should have been a capacitor between live and
ground inside the UPS.  Is this even possible?  Wouldn't that short the output during
normal use?

I still don't understand how the fuse blew...

Cnoob:
If your earth is connected to part of the UPS circuitry, then there is your potential current path.

malagas_on_fire:
A extension mains socket or single socket with included switch either for testing or turning off all loads when UPS is completly  powered off is also suitable.

hgg:
UPS OFF
Ground - Live : 230V
Ground - Neutral : 230V
Live - Neutral : 0V

I've connected an incandescent bulb between live and ground and the house RCD tripped.
The UPS does not isolate mains when switched off but it cannot also power anything from
live to neutral.  I have two devices connected.  A 3D printer power supply which is earthed
and the Raspberry Pi with its power adapter which is not earthed.  The Raspberry power
ON LED switches on and fades off every 5 seconds, only when one of its USB ports is connected
to the grounded 3D printer.  So it looks like its a kind of grounding issue.

I think I will include a main power switch as well.

malagas_on_fire:

--- Quote ---I've connected an incandescent bulb between live and ground and the house RCD tripped.

--- End quote ---

This is a dangerous move :S You've conected a resistive element between live and ground, so current will flow and RCD trips , probably more current and arcing :S The RCD has a self-test button to check this feature. Use the NCV /  EF ( Non Contact Voltage) to check isolation, but some cheap UPS have no isolation , even in the battery terminals .

About earth check if not creating ground loops  due to bad adaptor for the RPI, or use a 5V power supply that has grounding so the same loads has the same ground from the UPS. 

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