electrical.theiet.org/.../
Personally I think Rotary Isolator would be far better than 20 amp Double-pole switch shown Fig 2 as this allows for isolation and LockOff/LockOut
The cost of the Rotary Isolator is still quite low see URL below. (Other brands and other Wholesalers are available).
www.superlecdirect.com/.../
As always please be polite and respectful in this purely academic debate.
Come on everybody let’s help inspire the future
In my opinion the set of BS136x standards need thoroughly revising to introduce a greater factor of safety in the design of plugs, sockets, accessories to ensure they are fit for purpose across the full range of domestic applications, backed up by a more rigorous set of tests to ensure the devices being placed on the market meet those standards, not just when brand new and shiny, but after some surface oxidation/corrosion/wear-and-tear, to prove they are robust across their likely operating life.
In 2025 we should not be having to discuss topics like whether a 13A load can be used with a 13A accessory in a common household application, it should just work and work safely. But this is just one example of a broader problem, similar issues occur with long-duration loads on 13A sockets where it has become almost accepted belief that typical 13A plug/socket combinations are not suitable for supplying 13A for any significant length of time, hence the anxiety about using EV granny chargers or using high powered plug in heaters for any duration.
More significantly, why do we still have house fires, injuries and even fatalities from overloaded multiway socket/plug adapters, when electrical protection devices are now both readily available and cheap, capable of ensuring these devices are always safe regardless of how they are used or abused?
In my opinion the set of BS136x standards need thoroughly revising to introduce a greater factor of safety in the design of plugs, sockets, accessories to ensure they are fit for purpose across the full range of domestic applications, backed up by a more rigorous set of tests to ensure the devices being placed on the market meet those standards, not just when brand new and shiny, but after some surface oxidation/corrosion/wear-and-tear, to prove they are robust across their likely operating life.
In 2025 we should not be having to discuss topics like whether a 13A load can be used with a 13A accessory in a common household application, it should just work and work safely. But this is just one example of a broader problem, similar issues occur with long-duration loads on 13A sockets where it has become almost accepted belief that typical 13A plug/socket combinations are not suitable for supplying 13A for any significant length of time, hence the anxiety about using EV granny chargers or using high powered plug in heaters for any duration.
More significantly, why do we still have house fires, injuries and even fatalities from overloaded multiway socket/plug adapters, when electrical protection devices are now both readily available and cheap, capable of ensuring these devices are always safe regardless of how they are used or abused?
In 2025 we should not be having to discuss topics like whether a 13A load can be used with a 13A accessory in a common household application, it should just work and work safely.
I entirely agree.
In my opinion the set of BS136x standards need thoroughly revising to introduce a greater factor of safety in the design of plugs, sockets, accessories
Now I don't agree.
As with all standards, BS 1363 specifies a set of limits. So if a plug (etc.) experiences a greater temperature rise than 52 K, it has failed the type test.
I suspect that the better quality BS 1363 devices will barely get warm.
As Graham has pointed out, the fuse itself will heat up, but the pins have a considerably higher CSA. Granted the conductivity of brass is only about half of that of copper, but I cannot see their contributing much to any warming.
It seems to me that the fuse holder is probably the weakest link on the basis that the metal is relatively thin, it relies on spring pressure alone, and oxidization could increase the resistance.
As with all standards, BS 1363 specifies a set of limits. So if a plug (etc.) experiences a greater temperature rise than 52 K, it has failed the type test.
Equally important to the limits, are the test conditions and the factor by which they exceed nominal ratings, to provide that safety margin for when the equipment is in use and suffering some typical, in-use degradation.
In the case if a plug, if rated for 13A and your test current is 14A, so +7.7% in current, or +16% in terms of I^2R heating, that's not much of a safety margin to cover, as you mention, effects from degradation - fuse spring pressure, contact oxidation etc all of which will increase heating above that of a newly manufactured plug/socket/accessory.
Combine that with the rather generous (to the manufacturers) allowance of a +52.5 K temperature rise, so in normal 20 deg C ambient conditions allowing a touch temperature of 72.5 deg C, already at a level which causes burns to human skin. There's not a lot of margin to begin with and that's with newly manufactured devices.
For me, its interesting when you compare the approach in Electrical engineering, to other branches of engineering like mechanical and civil engineering, where much bigger factors of safety are typical, and indeed necessary.
so in normal 20 deg C ambient conditions allowing a touch temperature of 72.5 deg C, already at a level which causes burns to human skin
Well, I think that if you wanted to pull out the plug (in an emergency?) you would let go rather sharpish and not get burned. My interpretation of the standard was that the BS wallahs are more concerned about frying cables than consumers.
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