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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

    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.

  • 0 in reply to psychicwarrior

    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

  • 0 in reply to mapj1

    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.

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  • 0 in reply to psychicwarrior
    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.

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