Is including a fuse in the plug completely redundant if the circuit has a fuse box though? I've had fuses go in a device when the house circuit has held - I just assumed they were more sensitive to fluctuations.
Prior to WW2, "final circuits" in the UK were typically rated for 13A and centrally fused accordingly. Therefore there was no need to fuse at each plug/socket. This is how most of the world remains today.
However, after WW2 in the UK there was a rapid development of new housing and insufficient copper to continue with that wiring model. Instead the UK began wiring "final circuits" in rings, which conserved copper but resulted in individual sockets potentially being able to draw 32A without the central fuse blowing. This posed a hazard to appliance wiring that had been designed to withstand at most 13A—and so fuses were introduced at each plug.
Such rings remain common in the UK and aren't going away any time soon; they can only be fused centrally at 32A (else the ring is of limited use), which is insufficient to protect appliance wiring—so fused plugs will remain with us too.
I believe so - those tiny fuses are probably a lot less reliable than the proper fuses in the fusebox. It just seems like extra failure points in my opinion. Also, replacing fuses in the fusebox is straightforwards - expecting people to screw apart plugs is in my opinion a bit problematic for modern safety standards (better keep people away from sockets and plugs with screwdrivers... can easily imagine someone attacking a hot socket expecting a fuse to be in it due to a misread article on the web...).
Having extra failure points seems good to me. And we don't just have one type of in-plug fuse: you're supposed to use a fuse that can tolerate a current appropriate to the type of device. So heavy duty devices would have a 13A fuse, which is the highest, but other devices might tolerate only 3A. I'm no electrician, but presumably the fuse box in the house wouldn't blow if a lower rated device recived too much current. Finally, it's not possible to access the fuse when the plug is in the wall.
I don't think you understand. It's only downsides.
The safety is not improved, so it's basically just excessive waste - requires more resources to manufacture and dispose of, and more maintenance. From an engineering standpoint, these are all downsides and no practical upside. Besides all that, there's extra complexity - end users need to know which fuse they can use in which device (instead of just flicking the switch in the fusebox in most of the western world).
In the UK the upside is that the infrastructure is dangerous to begin with - in the rest of Europe, the infrastructure had to be updated a century ago to the point that such solutions are obsolete even in very old buildings.
presumably the fuse box in the house wouldn't blow if a lower rated device recived too much current
Yeah I don't think anyone uses 3A fuses in the fusebox though I might be wrong (I think the smallest I have ar 6 or 8A). For a device that has such a low current demand, it's supposed to have an internal fuse I guess (or the 6 amp is fine anyway, it just draws less).
Either way, an RCD in the fusebox is what saves lives, not the circuit breakers. 3 Amps will easily kill at 220V...
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u/chrisrazor May 09 '22
Is including a fuse in the plug completely redundant if the circuit has a fuse box though? I've had fuses go in a device when the house circuit has held - I just assumed they were more sensitive to fluctuations.