3 ms·

So I came across something like this once, UK 13A Plug -> 16A Ceeform Socket in an event and asked the guy (a professional with credentials) about it and he exp

So I came across something like this once, UK 13A Plug -> 16A Ceeform Socket in an event and asked the guy (a professional with credentials) about it and he explained that it was actually fine from a safety standpoint: (This happened a while ago, might have understood it slightly wrong) The 13A fuse was there to protect the thing from drawing more than 13A from the supply. After that it just doesn't matter - under a fault, nothing would be able to draw more than the lowest rated link. It's up to you to be aware that if you push it to 11 then things will fizzle out when the fuse goes, but no damage would be done. In this case it was just a couple of parcans so no issue. The dangerous combination would in fact be the opposite, a 32A Ceeform plug to 16A Ceeform socket unfused. Then it would be possible under fault to actually pass >16A through a thing only rated up to 16A. He said something along the lines of a 16/32A socket on the wall just means that the socket is capabale of handling 16A, not actually giving you that (or if it was even switched on) and in his line of work for anything needing more than 'a bit' of power they'd rather just tow their own generator in. This made sense as in the UK, which is different from a lot of the world, 13A sockets are usually backed by a ring main that will happily give you 32A - hence a fuse is mandatory by law in all plugs to protect the plug and flex leading from the plug to device and anything after that. Conversely, you can buy a cheap car inverter with a 13A socket perfectly legally, but try drawing that full 13A and see how far you get. Also note I'm just talking about amperage here, the voltage (i.e. blue ceeform 230V) must be the same throughout.

gambiting 6y ago
So I discovered something disturbing about UK plugs - yes, the fuse is 13Amps, but it's not like your main circuit breaker which trips instantly - no, those fuses take a long time to melt and break. I discovered this by accidentally drawing 20 amps through a single plug, because I was mistaken about the power draw of the two devices that were plugged into one extension cord. I only realized once I touched the cable and it was pretty hot(not melting yet, but definitely hotter than you want your cable to be) - I got a power draw meter and yep, I was drawing about 4.4kW(~20amps) through a plug equipped with a fully intact 13Amp fuse! I asked an electrician how can that be, and he said that yep, these fuses won't protect you from a higher draw that lasts a few minutes, the current needs to be either super high(like, not 20 but 50 amps) or prelonged enough to melt the fuse. That has....changed my perception of how these fuses are meant to work.
- alibarber 6y ago
  Interesting! I did not realise they were so slow to blow. But I also had a feeling that they may have also been intended as a poor-man's RCD back in the day: Your washing machine shakes the live loose and it touches the (thankfully earthed) metal case. Then you have a dead short across the fuse which should hopefully be enough to blow it pretty quickly..
- nucleardog 6y ago
  A typical breaker won’t blow instantly when you exceed the rated current either (unless you exceed it by a lot — like at least 5x). At less than double the rated current you could be waiting several minutes. So it’s not just a UK fuse issue. This isn’t really an issue. “Hot enough to concern you” is undesirable but not really what they’re worried about so much as “hot enough to combust”. And the alternative—if it were to blow instantly—is that your fuses would blow any time you turned something on with a high inrush current like a stand mixer or a vacuum cleaner.

gambiting 6y ago

So I discovered something disturbing about UK plugs - yes, the fuse is 13Amps, but it's not like your main circuit breaker which trips instantly - no, those fuses take a long time to melt and break. I discovered this by accidentally drawing 20 amps through a single plug, because I was mistaken about the power draw of the two devices that were plugged into one extension cord. I only realized once I touched the cable and it was pretty hot(not melting yet, but definitely hotter than you want your cable to be) - I got a power draw meter and yep, I was drawing about 4.4kW(~20amps) through a plug equipped with a fully intact 13Amp fuse! I asked an electrician how can that be, and he said that yep, these fuses won't protect you from a higher draw that lasts a few minutes, the current needs to be either super high(like, not 20 but 50 amps) or prelonged enough to melt the fuse. That has....changed my perception of how these fuses are meant to work.

alibarber 6y ago
Interesting! I did not realise they were so slow to blow. But I also had a feeling that they may have also been intended as a poor-man's RCD back in the day: Your washing machine shakes the live loose and it touches the (thankfully earthed) metal case. Then you have a dead short across the fuse which should hopefully be enough to blow it pretty quickly..
nucleardog 6y ago
A typical breaker won’t blow instantly when you exceed the rated current either (unless you exceed it by a lot — like at least 5x). At less than double the rated current you could be waiting several minutes. So it’s not just a UK fuse issue. This isn’t really an issue. “Hot enough to concern you” is undesirable but not really what they’re worried about so much as “hot enough to combust”. And the alternative—if it were to blow instantly—is that your fuses would blow any time you turned something on with a high inrush current like a stand mixer or a vacuum cleaner.