4mm cable into the bottom of main switch.

[Ian1981]

[QUOTE - So the 4mm is protected by the cut out fuse?]

For fault current yep but depends on what type supply

[QUOTE So by the cut out fuse then?
What other ocpd is there?]

What over current can the 4mm suffer when it can pull no more than 20 amp?

Overload protection is not the issue,How about short circuit protection?

 

[Wilko]

Could get a little toasty if the 1.5mm cpc ever got across the 100A fuse ...

 

[Marcus Vaughan]

Watching with interest - what I can't follow is where this 4mm comes from.

It must come from another db/ocpd?

 

[gazdkw82]

Assuming the main switch is a 100a/60a main switch then the 4mm is not suitable protected for over current and fault protection.

It's a c3 for me

 

[Ian1981]

It's the 20-A RCBO, as per original post.

No it’s not that is it will protect the 4mm against overload but short circuit protection is by the cut out fuse.

 

[Ian1981]

Not a C1 as it is not immediately dangerous, a C2 at worst but most likely a C3 or no code.

That narrows it down Dave haha

 

[gazdkw82]

The problem is, you can't rely on the 20a rcbo to protect the 4mm. What I mean by this is, future alterations, who's to say someone won't split that 4mm and feed something another db etc. There is nothing to protect that 4mm from overload.

It's the same as having a 1.5mm t+e for a lighting circuit protected by a 45a but at fused down to 6a at the first luminaire.

 

[Marcus Vaughan]

Watching with interest - what I can't follow is where this 4mm comes from.

It must come from another db/ocpd?

Sorry - confused by the post - I think the question I'm asking is what exactly is upstream of that main switch - what goes into the top?

 

[Pete999]

Assuming the main switch is a 100a/60a main switch then the 4mm is not suitable protected for over current and fault protection.

It's a c3 for me

It's a Bolls up for me

 

[Richard Burns]

A very poor installation but could be compliant if the connections are sound and the cable route to the 20A RCBO is suitable, then the RCBO can provide sufficient protection to be acceptable.
However there are a lot of caveats to the compliance so not generally a good idea.