2.5mm on 32A MCB

[kingeri]

Just wondering what folks would do if you came across this on your travels. 4mm radial sockets circuit, on 32A MCB. Two branches from the CU, one supplying 6 double sockets, wired entirely in 4mm, so fine. The other branch consists of a 1m run of 4mm to a double socket, then around 5m in 2.5mm cable on to a second double socket.

The question is, who would be happy to leave this arrangement in place, and who would downgrade the breaker to 20A? I would say it's ok, as the 2.5mm can't be overloaded as it feeds only one double socket, just like an infused spur off a ring.

 

[hightower]

In bah humbug mode - I think the max length by reg xyz is 3m

I'm not sure there is a regulation stipulating max length. I think the 3m length reg you are thinking of is specifically for pendants with smaller flex.

So a scenario: you need to install an extractor fcu and the ONLY circuit you have accessible to take it off is the cooker on a 32A breaker. Does that mean you take it from the cooker point in 4mm+ to the fcu, or would you take it in 2.5?

 

[kingeri]

Thanks everyone for the input. I am happy it was not just me who this got thinking.

 

[Wilko]

I'm not sure there is a regulation stipulating max length. I think the 3m length reg you are thinking of is specifically for pendants with smaller flex.

So a scenario: you need to install an extractor fcu and the ONLY circuit you have accessible to take it off is the cooker on a 32A breaker. Does that mean you take it from the cooker point in 4mm+ to the fcu, or would you take it in 2.5?

I think 433.2.2 gives us up to 3m grace (if I'm reading it right) to use the smaller cable to get to the fcu. I was thinking there had to be some give and take in the scenario you mention, but what limits it? 433.2.2 was all I found. Always happy to learn though

 

[westward10]

Still don't know how the 4mm is installed.

 

[westward10]

I'm not sure there is a regulation stipulating max length. I think the 3m length reg you are thinking of is specifically for pendants with smaller flex.

So a scenario: you need to install an extractor fcu and the ONLY circuit you have accessible to take it off is the cooker on a 32A breaker. Does that mean you take it from the cooker point in 4mm+ to the fcu, or would you take it in 2.5?

To shove 2.5 conductors in with 6.0 is just plain poor practice.

 

[hightower]

To shove 2.5 conductors in with 6.0 is just plain poor practice.

How so?

 

[kingeri]

Still don't know how the 4mm is installed.

Ref method C.

 

[Midwest]

Poor practice, but there you go.

I seem to remember someone starting a thread, annoyed at people stating something was 'Good practise', but here's a personnel statement that something is 'Poor practise'. You can't have it both ways

 

[kingeri]

I seem to remember someone starting a thread, annoyed at people stating something was 'Good practise', but here's a personnel statement that something is 'Poor practise'. You can't have it both ways

I agree. Also, it would be nice to have something more like, "I think that is poor practice because....".

I often see things which I think may not be the best way of doing something, but I can't automatically C2 it because I don't like it!

 

[davesparks]

How so?

the size difference between 2.5 and 6 means that the 2.5 is unlikely to be properly clamped by the terminal screw. With great care it is possible to do, but better to stick with similar sized conductors in one terminal.

 

[westward10]

I seem to remember someone starting a thread, annoyed at people stating something was 'Good practise', but here's a personnel statement that something is 'Poor practise'. You can't have it both ways

Ouch

 

[Dave OCD]

I'm not sure there is a regulation stipulating max length. I think the 3m length reg you are thinking of is specifically for pendants with smaller flex.

So a scenario: you need to install an extractor fcu and the ONLY circuit you have accessible to take it off is the cooker on a 32A breaker. Does that mean you take it from the cooker point in 4mm+ to the fcu, or would you take it in 2.5?

With this scenario I'd say it would be absolutely fine to run a 2.5, the current of an extractor fan would be minimal and a fraction of what 2.5 can carry so overcurrent protection isn't an issue. And the fcu would have an appropriate fuse [probably 3 amp] to protect the fan and its internal circuitry. As far as terminating a 2.5mm cable in the same terminals as 6mm there's no problem as long as it's done carefully.

 

[Deleted member 93172]

In my opinion for whats it worth, I am sure you cannot reduce the cable size without down rating the mcb, therefore in this instance a fused spur should be connected in circuit between the last 4.0mm fed socket and the 2.5mm fed socket.

 

[DPG]

In my opinion for whats it worth, I am sure you cannot reduce the cable size without down rating the mcb, therefore in this instance a fused spur should be connected in circuit between the last 4.0mm fed socket and the 2.5mm fed socket.

Not entirely true. Otherwise busbar systems wouldn't work. Daz

 

[Deleted member 93172]

Not entirely true. Otherwise busbar systems wouldn't work. Daz

Ah, but busbar systems have fused tap off boxes to feed equipment