elec. low power nightlight fusing/safety

I've just be taking a look inside one of them low power night lights. The kind that has a 13 amp plug as part of its construction so just plugs into a 13 A socket. It consists of a small pcb that does all the switching logic and drives a high-brightness led. It has a CE mark and is double insulated. Thing is, there is no sign of a fuse inside the unit. (Not that I can see anyway). So afaik we have a 0.6W device protected by the ring main rated mcb (15A/30A?) + RCD (30mA). So, 1) the device in normal operation is taking less than the trip current of the RCD (~2.5mA : 30mA ie 12 times less) 2) a fault in the device would easily melt the wires etc within in before getting anywhere near 15 or 30A. Just some thoughts on safety anyway. Make any sense?

Reply to
mike
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Sounds like a fuse to me...

Reply to
Andrew

You mean the wiring within the unit is designed to melt like a fuse!!!! I don't think I can belive that one.

Reply to
mike

Fuses only really protect power leads, and as the device doesn't have a power lead (and it's going to fail open circuit long before the mains wiring gets warm) I don't think you need to worry :-)

Reply to
Rob Morley

Sometimes a weakness in a PCB link would act as a low current fuse...

Reply to
Phil

I'm not worried - just interested - it seemed a little incongruous that's all.

Reply to
mike

Fuses come in a few different forms, some of which look nothing like traditional glass or ceramic fuses. But these types of products usually use a safety resistor instead. This is a series resistor that does 2 jobs.

  1. it reduces inrush current
  2. if it gets too hot it fails safely open circuit, thus acts like a slow thermal fuse.

These effectively give very low current fusing.

Thin PCB tracks will fuse too, but they would be limited to LV use, you wouldnt want to do that for mains fusing. A fuse wire link soldered into the pcb will have the same problem, burnt pcb would tend to bridge the fuse, so its not good enough on mains.

NT

Reply to
bigcat

Likely, the PCB itself would fail close to the pin connections if there was some form of overload.

Reply to
Dave Plowman (News)

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