What is application of Load-Switch + Disconnector?

That rather depends on the load, the supply, the rating of the cables, and practice varies to a degree by country as well. Normally there are many layers of ADS (Automatic Disconnection Supply) , with ratings getting more and more sensitive towards the final load. For ease of writing, I will use 'fuse' as short form for ADS protective device, but realise it could be a fuse or mcb, or MCCB  or some other kind of  breaker, but than it gets very long-winded to keep saying so.

There is always 'death or glory' fuse of some kind at the origin of the installation. That is mainly to protect the substation transformer, or generator or whatever. However, if the cables that follow it are suitably rated to survive if they were shorted, and low enough resistance to ensure that the fuse at the origin operated, then the cables  need no additional fault protection. There may be distribution circuits (submains, laterals, distributors depending on what nationality and age you are) that are more lightly fused and take power to another fuseboard, maybe with an switch or not, for fusing down for final circuits, or all final circuits may run back to the origin. The final circuit will normally be supplied via its own fuse. A consumer unit is nothing more than an isolator and some fuses sharing the same box, they could have been separate. (I often wish they were but that is another matter)

It may be that even the final circuit fuse is not fine enough for the load, so there is a local fuse at the equipment, and there may be another switch at that point too.

The key thing to realise, is that order is not rigid - if the fuse precedes the switch, that may allow a switch with a lower rating,, if the switch is first, you can turn it off to work on the fuseboard safely.

So for a realistic-ish  example a 100A fuse and a 100amp circuit looping round to feed a few 30A breakers each feeding a 30A switch with  a < 30A load on each is perfectly sensible.


Equally, a 100A switch feeding a 100A main, feeding  a few 30A breakers each beside  a < 30A load is also perfectly acceptable,

But these are solutions to two different problems.

('How do I isolate this whole room full of equipment quickly from one point?' instead of

'How do I make this one machine safe to allow someone to clean or repair it, and keep the rest of the factory turning?')

Both are common requirements, in different situations. You quite commonly find a mixture of both approaches

That rather depends on the load, the supply, the rating of the cables, and practice varies to a degree by country as well. Normally there are many layers of ADS (Automatic Disconnection Supply) , with ratings getting more and more sensitive towards the final load. For ease of writing, I will use 'fuse' as short form for ADS protective device, but realise it could be a fuse or mcb, or MCCB  or some other kind of  breaker, but than it gets very long-winded to keep saying so.

There is always 'death or glory' fuse of some kind at the origin of the installation. That is mainly to protect the substation transformer, or generator or whatever. However, if the cables that follow it are suitably rated to survive if they were shorted, and low enough resistance to ensure that the fuse at the origin operated, then the cables  need no additional fault protection. There may be distribution circuits (submains, laterals, distributors depending on what nationality and age you are) that are more lightly fused and take power to another fuseboard, maybe with an switch or not, for fusing down for final circuits, or all final circuits may run back to the origin. The final circuit will normally be supplied via its own fuse. A consumer unit is nothing more than an isolator and some fuses sharing the same box, they could have been separate. (I often wish they were but that is another matter)

It may be that even the final circuit fuse is not fine enough for the load, so there is a local fuse at the equipment, and there may be another switch at that point too.

The key thing to realise, is that order is not rigid - if the fuse precedes the switch, that may allow a switch with a lower rating,, if the switch is first, you can turn it off to work on the fuseboard safely.

So for a realistic-ish  example a 100A fuse and a 100amp circuit looping round to feed a few 30A breakers each feeding a 30A switch with  a < 30A load on each is perfectly sensible.


Equally, a 100A switch feeding a 100A main, feeding  a few 30A breakers each beside  a < 30A load is also perfectly acceptable,

But these are solutions to two different problems.

('How do I isolate this whole room full of equipment quickly from one point?' instead of

'How do I make this one machine safe to allow someone to clean or repair it, and keep the rest of the factory turning?')

Both are common requirements, in different situations. You quite commonly find a mixture of both approaches