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UK diy (uk.d-i-y) For the discussion of all topics related to diy (do-it-yourself) in the UK. All levels of experience and proficency are welcome to join in to ask questions or offer solutions. |
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elec. low power nightlight fusing/safety
"mike" wrote in message ... Thing is, there is no sign of a fuse inside the unit. (Not that I can see anyway). .... 2) a fault in the device would easily melt the wires etc within in before getting anywhere near 15 or 30A. Sounds like a fuse to me... |
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Sometimes a weakness in a PCB link would act as a low current fuse...
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mike wrote:
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? 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 |
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In article ,
mike wrote: 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. Likely, the PCB itself would fail close to the pin connections if there was some form of overload. -- *I almost had a psychic girlfriend but she left me before we met * Dave Plowman London SW To e-mail, change noise into sound. |
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