Switch Fuse's

[wreck-it-steve]

I see a lot of switch Fuse's in factories etc where a SWA cable will come from the DB to feed a machine but before it hits the machine there will be a switch fuse before it...

Why do this when there is a breaker protecting it? Why not just use an isolator as required..

Only asking as I've always wanted to know

 

[Iggifer]

Could be the cable is fed from say a 45a breaker and 10mm cable, and is then fused down for say 4mm cable and 30 amps etc

Makes it easier to change if the equipment changes than if you did the whole run in 4mm

 

[wreck-it-steve]

Thanks for your reply. That's makes sense now. Bit if the cable was say 4.0mm protected by a 32amp MCB feeding machine that draws 32 or so amp then is there much point having say a 32 amp switch fuse over a standard isolator?

 

[JohnW2]

Thanks for your reply. That's makes sense now. Bit if the cable was say 4.0mm protected by a 32amp MCB feeding machine that draws 32 or so amp then is there much point having say a 32 amp switch fuse over a standard isolator?

If you're talking about 4mm flex, or any other type of 4mm cable which has a CCC of at least 32A, then, no, I can see no point - but maybe others can!

Kind Regards, John

 

[Lectrician]

It's old school. Rotary isolators these days.

 

[ericmark]

It may be a stores thing. When I ran a stores we had to reduce stock for it to fit every thing in. So we went for preferred sizes SWA in stock was 6mm² and our outlets were 32A three phase sockets with a MCB built in. So if we wanted to replace something in a hurry it would have to be what we had in stock. If we had more time we would order up what was required, but we could not keep everything in stock so a 32A socket without any automatic disconnection device was rare.

Where fuses are used it also means electricians can remove fuses and place them in their box when working on the equipment. It is all well and good talking about personal locks, but normally an electrician only has one or two so it reaches a point where he has run out of locks. Having the fuses in a cabinet in the workshop means electricians are forced to go to the workshop so will read reason why removed. From bitter experience having locks with like keys and only electrician have the key it is too easy for mistakes to happen. Hence my mauled right hand.