Should ring main live return to same MCB?

[electronicsuk]

Highlights again the problems of remote diagnostics and assumptions

Well, we're only as good as the information provided to us, but we can't help that!

 

[Chri5]

So at least we can now clear that up. Playing up in someone else's post when the op may well take what you posted as fact is naughty.

Your post mentions 32amp mcb's and regs that allow radial 2.5mm feeds, no where does it caveat that comment with "only 1 x socket".

Please remember this site is to help, posting 'grey area' advice isn't helpful.

 

[securespark]

Appx 15 states that you can fit a 2.5 unfused spur to a 32A Ring Final circuit, feeding one outlet. Or an FCU can be used to supply several outlets wired in min. of 1.5mm² T&E.

On a 20A Radial Final circuit, a minimum of 2.5mm² T&E must be used.

On a 32A Radial Final circuit, a minimum of 4.0mm² T&E must be used.

HOWEVER, an unfused spur can be taken from any point in the circuit in 2.5mm² (including at the origin of the circuit), providing it feeds only one single or twin outlet.

 

[ban-all-sheds]

Highlights again the problems of remote diagnostics and assumptions

Don't make them, then...

 

[SUNRAY]

Highlights again the problems of remote diagnostics and assumptions

Don't make them, then...

My point exactly

 

[SUNRAY]

Appx 15 states that you can fit a 2.5 unfused spur to a 32A Ring Final circuit, feeding one outlet. Or an FCU can be used to supply several outlets wired in min. of 1.5mm² T&E.

On a 20A Radial Final circuit, a minimum of 2.5mm² T&E must be used.

On a 32A Radial Final circuit, a minimum of 4.0mm² T&E must be used.

HOWEVER, an unfused spur can be taken from any point in the circuit in 2.5mm² (including at the origin of the circuit), providing it feeds only one single or twin outlet.

Yep your dead right it is permissible to install a double socket using a cable rated at 28ishA derated to say 50% or 14A by insulation, temperature etc on a 32A breaker or 30A fuse running a 6Kw load.

There are facilities in the regs to use a (restricted length of) cable which is protected down stream. That certainly happens on a regular basis within control panels where the tap off a busbar will be rated for the protective device on the end of it rather that the device that feeds it.

 

[electronicsuk]

Yep your dead right it is permissible to install a double socket using a cable rated at 28ishA derated to say 50% or 14A by insulation, temperature etc on a 32A breaker or 30A fuse running a 6Kw load.

There are facilities in the regs to use a (restricted length of) cable which is protected down stream. That certainly happens on a regular basis within control panels where the tap off a busbar will be rated for the protective device on the end of it rather that the device that feeds it.

Although we're getting pretty pedantic now, and I agree in principal especially with reference to control panels, you couldn't use this regulation to justify a 6kW load on a cable with a rated design current of 14A. That goes against all the basic circuit design principles.

 

[SUNRAY]

Yep your dead right it is permissible to install a double socket using a cable rated at 28ishA derated to say 50% or 14A by insulation, temperature etc on a 32A breaker or 30A fuse running a 6Kw load.

There are facilities in the regs to use a (restricted length of) cable which is protected down stream. That certainly happens on a regular basis within control panels where the tap off a busbar will be rated for the protective device on the end of it rather that the device that feeds it.

Although we're getting pretty pedantic now, and I agree in principal especially with reference to control panels, you couldn't use this regulation to justify a 6kW load on a cable with a rated design current of 14A. That goes against all the basic circuit design principles.

The whole point about my post is that a ring final spur may be made using 2.5mm cable and it may be derated to around 14A by the conditions its in and it may have a double 13A socket on the end of it and there may be a 3Kw device pluged into each socket. And yes I have seen exactly this too many times and earnt a lot of money correcting the resulting damage.

That goes against all the basic circuit design principles.

NO
Thats all in the regs and may be fitted in every other house in the country.

 

[ban-all-sheds]

Your post mentions 32amp mcb's and regs that allow radial 2.5mm feeds, no where does it caveat that comment with "only 1 x socket".

Yes it does - read 433.2.

 

[ban-all-sheds]

Yep your dead right it is permissible to install a double socket using a cable rated at 28ishA derated to say 50% or 14A by insulation, temperature etc on a 32A breaker or 30A fuse running a 6Kw load.

No it is not.

 

[ban-all-sheds]

The whole point about my post is that a ring final spur may be made using 2.5mm cable and it may be derated to around 14A by the conditions its in and it may have a double 13A socket on the end of it

No it may not.

and there may be a 3Kw device pluged into each socket. And yes I have seen exactly this too many times and earnt a lot of money correcting the resulting damage.

And the reason you see damage is because it's not in compliance with the wiring regulations.

NO
Thats all in the regs and may be fitted in every other house in the country.

It may be commonly encountered, but it is NOT in the regulations.

 

[ajrobb]

So if the wires are sorted, I'll have 4 wires to the one mcb, which means 2 ring circuits off one mcb. I guess that is allowed, and I don't need to get a new CU with another 32A point...?

You started with 2 MCBs and you've got 2 rings. Why not rearrange to give you one ring per MCB?

 

[ban-all-sheds]

Err...

The consumer unit is about 20 years old, and the holes for live feed to each mcb are about 4mm wide with 3 twisted cables in.

I think you'll find that 3 cables in each of 2 MCBs is unlikely to be 2 rings...

 

[ajrobb]

Err...

The consumer unit is about 20 years old, and the holes for live feed to each mcb are about 4mm wide with 3 twisted cables in.

I think you'll find that 3 cables in each of 2 MCBs is unlikely to be 2 rings...

Sorry, I misunderstood.

Now for another silly suggestion. If the 2 smaller ring mains cover less than 100 sq m together, cannot they be rewired in series as a single ring?

 

[ban-all-sheds]

Subject to considerations of volt-drop, EFLI and 314, yes.