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.

 

[Charlie_]

Under fault conditions what is the maximum current/time a 4mm t+e can withstand?
What size fuse is protecting the 4mm cable from L to N & L to E faults?

 

[Lucien Nunes]

you can't rely on the 20a rcbo to protect the 4mm. What I mean by this is, future alterations,

It is not necessary or possible to protect an installation against incorrect future modifications. All systems can be modified so that they become dangerous.

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.

Not quite the same. Top of head without checking the numbers, think the 1.0mm² CPC would not be protected against fault current by a 45A fuse, whereas I think the 4mm² is protected by the cutout as would be any other tails if the CPC is 4mm² too, but if it's T+E, would have to look it up, sounds doubtful as mentioned above.

But the crux is 433.2.2 which allows OPD to be located somewhere other than at the source of the circuit, so long as certain criteria are met to reduce the probability of a fault on the circuit up to where the OPD is. It may be the case there that those criteria are met, whereas I don't think they would be on your hypothetical lighting circuit.

E2A:

What do you mean by in the bottom of the main switch.

what goes into the top?

Agreed, we should refer to supply side and load side. Those of us who spend most of our time with TP+N DB's are used to putting the supply into the botttom of the switch.

 

[Charlie_]

I would just code it badgers arse

How useful would that be if that was an actual code..
So many times I have seen horrific looking installations that still comply

 

[Wilko]

Hi - in order to make use of 433.2.2 as they’ve done I think they need to install the cable with specific protection against impact (say in metal conduit). Which I’m guessing won’t have been done. Reg 433.2.2 refers us to 434 and then 434.2.1 (ii) .

 

[westward10]

If the enclosure it supplies is metal the cpc must be able to withstand fault current.

 

[Wilko]

If the enclosure it supplies is metal the cpc must be able to withstand fault current.

Agree, I didn’t want to be tooo presumptive but even a 63A fuse will need more than 1.5mm ...

 

[SparkyAndGeorge]

Code 3

 

[Deleted member 26818]

Hi - in order to make use of 433.2.2 as they’ve done I think they need to install the cable with specific protection against impact (say in metal conduit). Which I’m guessing won’t have been done. Reg 433.2.2 refers us to 434 and then 434.2.1 (ii) .

That is not the case.
Generally tails are not contained in conduit, the mechanical protection is provided by the sheath.
Hence why we no longer allow unsheathed tails.

 

[Dustydazzler]

Code Red

 

[snowhead]

Code Red Brown

I've Harmonised that for you.