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why might one use a fuse-switch isolator instead of a switch-fuse isolator - what really is the definitive difference ?

psychicwarrior

good morrow

as per the 'subject' - when might one be used over the other and construction wise in an enclosure, what is the difference* ?

seperate to that, is it important to have the supply on the moving pole of the switch or the fixed side (if that makes sense) ?

the symbols are different too between the two types  - one appears to show the fuse on the angled line of the switch where as on the other, it is on the horizontal line seperate from the switch.

the internet seems to not have an answer - at least on the basis of carrying out a nano-second search ;-)

thank you

*  is the only difference being that the fuse also protects the switch, in a fuse-switch isolator...

edit: no idea what i typed but edited the symbols sentence to read 'between the two types', which it wasnt originally

edit2: rather bizarrely, the * sentence was erased to be replaced by 'edit spelling' ...  i didnt erase the original entry there.  strange.  ive put it back as it was near enough once noticed. sorry.

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  • 0 in reply to Chris Pearson

    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

  • 0 in reply to Chris Pearson
    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.

  • 0 in reply to gkenyon
    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

  • 0 in reply to Chris Pearson

    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

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