Obvious question more than likely.

[jwc]

Second question of mine on here and it's one I've never got round to getting an answer for.


Mains comes into a building through a 60A main fuse for instance.
Why then are main switches rated at 100A or 80A?
Does this mean any load above 60A would blow the main fuse before it blew the main breaker?


Don't be harsh people. I'm fully aware the answer's probably an obvious one.

 

[ian.settle1]

On a similar vane I had an electrician with 2391 who carried out a PIR and recommended that a 40A 30mA RCD should be changed to a 32A one, asked him why he replied because the fuse protecting the circuit is only 32A thus it would go before the RCD if the was an earth fault and not the RCD as it was rate at 40A, shook my head and walked away in disbelieve

 

[Guitarist]

There is a simple reason for switches being 100A.... They can be used on a system with a 60A fuse, an 80A fuse, or a 100A fuse. In other words, one size fits all.
As already said, a switch is just that, the same way as an RCD is just that...they do not "trip" on overcurrent. While I agree that nobody knows everything, this is pretty basic stuff.

 

[SirKit Breaker]

But why have a main switch rated at 80A if the main fuse is only 60A?

Because thats what the manufacturer makes, and it will do for any supply rated at 80a or less.

 

[dan86]

I was refraining from saying anything, but it seems like the rest of you haven't held back! I agree with jamesBoater. how can the OP not know this basic knowledge after having gained said quals?!

 

[richy3333]

Thanks for the explanation, Darkwood. I've completed a full apprenticeship, AM2 and NVQ Level 3. Everything's much clearer now knowing that the main switch is exactly that... A switch.

FFS and people on this forum lambast Electrical Trainee!

Stick a 63A Main switch in and everyones happy?!

 

[SPARTYKUS]

FFS and people on this forum lambast Electrical Trainee!

Stick a 63A Main switch in and everyones happy?!

fair comment. Och aye.

 

[richy3333]

fair comment. Och aye.

Don't bring racism into it too

 

[trev]

Sore point Richy, some knacker accused me of that in a roundabout waylast night on here. Least said soonest mended bonny lad

 

[richy3333]

trev your'e the last person I'd think of a racist. Tell em to **** in their hat and punch it! (not a very scottish term, but its what came to mind)

 

[SPARTYKUS]

Don't bring racism into it too

Ahh dinna ken wha yer sayin, laddie ;-)

 

[ipf]

trev your'e the last person I'd think of a racist. Tell em to **** in their hat and punch it! (not a very scottish term, but its what came to mind)

Could use their sporran, then

 

[trev]

There's a French saying, Je te pis au cour
Something like that anyway, I should have said that to him

 

[brightspark2010]

a lot of domestic propeties have a 100a main fuse so why do many domestic boards have 100a main switch then 80/63a rcds surely there is potential for overload under fault conditons or am I missing something silly?

 

[telectrix]

because there are 2 80/63A RCDs, hopefully the load is reasonably equally shared between them.

 

[brightspark2010]

ok good point but isnt that similar to say a 10 amp lighting circuit with 5amp switches in different rooms surely the light switch is underated and could be overloaded under fault conditions?