It is perfectly possible to design a fuse holder where you can take the fuse but leaving the bits that were serving as contacts to it live, and not have that exposed to touch, A switch part is not a requirement to be able too change the fuse

I have never been a great fan, but at least one design of house cut-out achieves this in that the fuse comes out  on carrier, and leaves finger contact-able  live metal behind, EXAMPLE - no upstream switch needed.

Mike

Chris Pearson said:

If the fuse(s) remain connected to the supply side, how do you change them?

Isolate the supply (at he supply if necessary)

mapj1 said:

A switch part is not a requirement to be able too change the fuse

Agreed ... no matter whether it's a switch-fuse or fuse-switch. With either, there could be parts to change, that may remain live when the switch is in the open position.

There are, however, designs that remove both sides of a fuse when a switch-fuse or fuseholder is opened, to facilitate safe changing of the fuse regardless of whether either side is energized.

We will need to think about these issues a little more carefully as we move forward with embedded generation and energy storage.

With the terms fuse-switch and switch-fuse, I was thinking there was an implied order (of switch and fuse) in the two terms. It would seem not ?

For a symbol , is there an implied 'supply side' ?  As the switch is either before or after , depending, the fuse.

And of course by dint of relabeling the input and output terminals, if they wished the manufacturer could  make both models on  the same production llne . As I said above, in practice manufacturers and sales catalogues etc are not especially consistent. (notwithstanding the moving fuse part of the above drawings, usually both sides of the fuse get disconnected when you need to change it.)

And, as per Grahams point, with things like generator switching, both sides could be supply side in the same installation but under different sets of conditions.

M

thank you

do you have a real-world scenario where a 'fuse-switch'  (fuse on the switch mech.)  is preferable to a switch-fuse please ?

my experience leaves me with no idea im afraid.

psychicwarrior said:

my experience leaves me with no idea im afraid.

I think that's because it's a more historical anecdote really, but switch-fuses used to be smaller for the same functionality, so often found with higher current applications (say > 125 A)

But, with some novel designs, that isn't necessarily the case these days.

Also the observation for anyone who isn't aware of the drawing symbols, but the circle contact makes it a "suitable for regular switching" type device, and the line perpendicular to the current-carrying conductor means the device is suitable for isolation (disconnector in switchgear standard terms).

So, the switch-disconnector-fuse or fuse-switch-disconnector has the highest level of functionality, if you will, being suitable for both regular functional switching as well as use as an isolator, and could be the most expensive in the range.

gkenyon said:

Chris Pearson said:

If the fuse(s) remain connected to the supply side, how do you change them?

Isolate the supply (at he supply if necessary)

mapj1 said:

A switch part is not a requirement to be able too change the fuse

Agreed ... no matter whether it's a switch-fuse or fuse-switch. With either, there could be parts to change, that may remain live when the switch is in the open position.

There are, however, designs that remove both sides of a fuse when a switch-fuse or fuseholder is opened, to facilitate safe changing of the fuse regardless of whether either side is energized.

We will need to think about these issues a little more carefully as we move forward with embedded generation and energy storage.

Having a separate isolator seems to be unnecessary - isn't the whole idea that one device does it all?

The attached brief article may help, but I notice that the diagrams are the opposite way round to psychicwarrior's so does the fuse come before or after the switch/isolator? Or indeed, even if supply and load are marked, what is there to stop a device being connected back to front?

If the fuse carrier is the moving part, it is easy to see how it can be isolated at both ends to facilitate changing of a fuse - e.g. Eaton Glasgow.

PDF

I note with wry amusement, that although the pictures show a moving fuse and label it 'fuse-switch disconnector, they have carefully avoided a written definition beside the picture, while for the others there is one. Perhaps they are not that confident either.

Mike