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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.

  • 0

    Part 2 may be helpful.

    Switch: "A device designed to make or break the current in one or more electric circuits."

    That only needs to break the line conductor.

    Isolator: A switch which isolates a part of the installation.

    Isolation: "Function intended to make dead for reasons of safety all or a discrete section of the electrical installation by separating the electrical installation, or section thereof, from every source of electrical energy."

    So that is more than just switching. The neutral (if any) also needs to be disconnected.

  • 0 in reply to Chris Pearson

    i might not have worded my splurb too well, as that is not related to the 'questions (with ?)' to my mind ... 

    :-)

  • 0 in reply to Chris Pearson
    Chris Pearson said:
    The neutral (if any) also needs to be disconnected.

    Except when it doesn't. Reg 461.2

  • 0 in reply to gkenyon
    gkenyon said:
    Chris Pearson said:
    The neutral (if any) also needs to be disconnected.

    Except when it doesn't. Reg 461.2

    Rolling eyes

  • 0

    I think one needs to read the data sheets carefully, and then think about the end use, I fear that what means in practice can be rather like Alice in Wonderland.

    When I use a word,' Humpty Dumpty said in rather a scornful tone, 'it means just what I choose it to mean — neither more nor less.


    It may mean that the switch isolates the fuse holder, or that removing the fuse isolates the switch. It may not.
    Isolator, switch and disconnector are defined in the degree of safety and the ability to open under load or fault .
    But if 'fuse' precedes or follows in the language and is the same electrically is probably a bit of a lottery.
    Mike.

  • 0

    In my experience the fuses are part of the moving mechanism in a fuse-switch whereas in a switch fuse they are stationary.  I suspect that the definition is manufacturer dependent though.  Moving fuse carriers can often mask live contacts giving an air of added safety not that this should be taken for granted as some mechanisms are quite flimsy.

  • 0 in reply to statter
    statter said:
    In my experience the fuses are part of the moving mechanism in a fuse-switch whereas in a switch fuse they are stationary.

    Yes, these are the definitions used in the product standards:

  • 0 in reply to gkenyon

    thank you

  • 0 in reply to statter

    thank you for that

    where would a fuse-switch isolator be prefereable to a switch-fuse isolator - or is simply about protecting the switch  (in addition) for a fuse-switch  for whatever reason ?

  • 0

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

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