When your mind starts drifting as you work auto-pilot....

[SPECIAL LOCATION]

I am not after an answer as such...

Just something I was pondering while doing a quick little Friday afternoon job today..

(Adding a double socket in a porch direct through wall to CU less than 2m away.)

So as I am doing my bits.. 

(Connected my new socket as a spur onto an existing circuit at CU...)

I was thinking...

An existing 32A ring circuit could have multiple 2.5mm T&E spurs taken from any point around the ring, including the CU MCB terminations, 

each supplying 1x double socket off each spur taken from it.. 

(no specific length of each spur, just that it only supplies a single accessory.) 

BUT..

What if a 32A MCB had 5x 2.5mm radials directly connected to it, each supplying 1x double socket at the end of each cable..?

No actual ring at all..

Just 5x 2.5mm T&E radials, each 25m long with 1x double socket, directly back to a common single 32A MCB ?

Would this be considered acceptable? compliant?  poor workmanship? sneaky? dubious? other?

Guinness

:|  

 

[binky]

a very good question. This brings us back to a long winded discussion about loading of cables, ie if what is conected to the end of the cable cannot overload the cable, then the MCB is more or less irrellevant bar short cct protection. It's the same argument that applies to commercial lighting, ie a cct wired in say 2.5mm cable on a 20A MCB with 1mm flex drops to single light fittngs. As long as the light fitting cannot over load the flex drop cable, it is considered acceptable. 

 

[poni]

you can only as one spur for each socket/ fcu connected to the ring , so if you had 5 spurs off the ring you would need 5 sockets or fsu connected to the ring in the first place 

 

[Bruspark]

For a start you would have too many cables in the MCB terminal

 

 

[SPECIAL LOCATION]

For a start you would have too many cables in the MCB terminal

 

Where does it state the maximum number of conductors permissible? 

as opposed to the max CSA a terminal is designed for?

Guinness

 

[binky]

you can only as one spur for each socket/ fcu connected to the ring , so if you had 5 spurs off the ring you would need 5 sockets or fsu connected to the ring in the first place 

it's always shown as that, but electrically if you wired a large junction box into the ring and spurred off mulltiple times, what difference does it make to current carrying capacity of the cables? 

 

[SPECIAL LOCATION]

you can only as one spur for each socket/ fcu connected to the ring , so if you had 5 spurs off the ring you would need 5 sockets or fsu connected to the ring in the first place 

But this isn't a ring..

its multiple radials each having no different loading than the legs of a spur if they had been a ring..

Not aware of any restrictions on the number or positions or branches off a 20A radial circuit.. ?

Assuming you can make the joint mechanically sound would 5x 2.5T&E single accessory load radials be ok into a 20A MCB?

if yes why not a 32A MCB. ?

Been trying to think of any specific regulations that relate to this.. 

:C

Its a bit similar to the old 6.0mm radial feed 2.5mm ring lollipop circuit concept.

To look at it another way, what if it was..

32A MCB -> 6.0mm radial -> J/Box -> 5x 2.5 radial to single accessory.. 

Guinness

 

[binky]

But this isn't a ring..

its multiple radials each having no different loading than the legs of a spur if they had been a ring..

Not aware of any restrictions on the number or positions or branches off a 20A radial circuit.. ?

Assuming you can make the joint mechanically sound would 5x 2.5T&E single accessory load radials be ok into a 20A MCB?

if yes why not a 32A MCB. ?

Been trying to think of any specific regulations that relate to this.. 

:C

Its a bit similar to the old 6.0mm radial feed 2.5mm ring lollipop circuit concept.

To look at it another way, what if it was..

32A MCB -> 6.0mm radial -> J/Box -> 5x 2.5 radial to single accessory.. 

Guinness

getting a good mechanical grip on 5 cables in one MCB would be challenging to say the least, so I would say (without trying it) it would fail good work practice in respect to producing a mechanically sound electrical connection. 

Radial, JB and 5 spurs, as I said above, I see no reason why that is an issue electrically if no spur can be overloaded by whatever is connected to the end of it. Double sockets being rated as 20A of course. 

 

[Bruspark]

Where does it state the maximum number of conductors permissible? 

as opposed to the max CSA a terminal is designed for?

Guinness

Seriously ??   

Clearly 2 are OK as Rings are OK,
beyond that one or more conductor may be looser than the others or barely caught at all   - So bad practice 

 

[poni]

Assuming you can make the joint mechanically sound would 5x 2.5T&E single accessory load radials be ok into a 20A MCB?

if yes why not a 32A MCB. ?

then why have any fuses at-all just rely on the service head to do the job ,just run all circuits in single radials(lights, sockets, cookers, and showers) save the money on the consumer unit 

 

[Hefferl]

Seriously ??   

Clearly 2 are OK as Rings are OK,
beyond that one or more conductor may be looser than the others or barely caught at all   - So bad practice 

Surely 3 are ok too as you can legitimately spur from a ring at the mcb (as is being done here)

 

[Bruspark]

Surely 3 are ok too as you can legitimately spur from a ring at the mcb (as is being done here)

Yes its 'legitimate but tricky' to have 3 in one terminal and seems more prone to trouble on later testing, 


My point was that while there's no absolute 'stop right there' point it gets increasingly dodgy and I personally couldn't look myself in the mirror if installing with 5 !   

Even if it's ok initially the chances it loosens off over time or if the conductors 'get wiggled'  are pretty high

Kinda' thinking I've stumbled into the DIY forum here.  I'd have been ridiculed all week for even suggesting this 40 years ago, but maybe that's progress  

 

[SPECIAL LOCATION]

Seriously ??   

Clearly 2 are OK as Rings are OK,
beyond that one or more conductor may be looser than the others or barely caught at all   - So bad practice 

Erm..    :C

How have we managed for years and years with the traditional circular junction box with four cables terminated together..?

such as...

https://www.toolstation.com/axiom-junction-box/p73144

So for example a not too rare lighting circuit arrangement ..

supply in + supply out + loop to switch + loop to light fitting..

Where we have:-

3x Perm live conductors in terminal 1.

2x Switched lives in terminal 2.

3x Neutrals in terminal 3.

4x Earth (CPC) in terminal 4.

Now if I were a gambling man.. 

I would be betting that 99.99% of competent electricians would say they they could easily terminate the 4x CPC conductors, (mechanically secure), into a screw terminal..?

And would probably say that adding and extra 1 wouldn't be too hard..?

But for the sake of arguments lets imagine we have put all of our conductors into a mechanical crimped lug..

Is there any major BS761 non-compliance with a 32A MCB supplying 5x 25m long 2.5mm T&E radials with a single double 13A socket on the end of each?

(no mention of all the strands on a concentric cable being terminated securely)..

But interesting thought exercise gents..

Guinness

Basically echoing many of the various thoughts going through my mind on Friday while I was adding my customers Christmas-lights socket in their porch!

:Salute

 

[kerching]

4 cables into a JB?!....Noooooooooooooooooooooooo!

ive seen far far more than that! Even more if you adopt the 60s practise of external,earth twisting.  This must, obvs, be done across the JB lid so tight that the lid cannot be removed.

Ashley even brought out an external earthing clamp terminal to mount the JB onto

 

[Geoff1946]

Coming back to power wiring, surely its the rigidity of the 2.5 wire, coupled with the often limited space in the backboxes, (and hence force applied when finally pushing the accessory in), which can lead to poor connections to multiple cores?

 

[Bruspark]

Erm..    :C

How have we managed for years and years with the traditional circular junction box with four cables terminated together..?

such as...

https://www.toolstation.com/axiom-junction-box/p73144

So for example a not too rare lighting circuit arrangement ..

supply in + supply out + loop to switch + loop to light fitting..

Where we have:-

3x Perm live conductors in terminal 1.

2x Switched lives in terminal 2.

3x Neutrals in terminal 3.

4x Earth (CPC) in terminal 4.

Now if I were a gambling man.. 

I would be betting that 99.99% of competent electricians would say they they could easily terminate the 4x CPC conductors, (mechanically secure), into a screw terminal..?

And would probably say that adding and extra 1 wouldn't be too hard..?

But for the sake of arguments lets imagine we have put all of our conductors into a mechanical crimped lug..

Is there any major BS761 non-compliance with a 32A MCB supplying 5x 25m long 2.5mm T&E radials with a single double 13A socket on the end of each?

(no mention of all the strands on a concentric cable being terminated securely)..

But interesting thought exercise gents..

Guinness

Basically echoing many of the various thoughts going through my mind on Friday while I was adding my customers Christmas-lights socket in their porch!

:Salute

I was not talking about lighting circuits  -  wrapping 8 twisted stranded corroded conductors in sellotape always used to be fine there

But for power and a MCB I would be betting that 99.9999999999% of competent electricians would say they they could easily
torque it up satisfactorily without a gauge - but we now know we were wrong all those times 

 

[Andy™]

see similar all the time... 32a ring with a spur from the MCB, perfectly fine... remove the ring and have just the 2.5 feeding a socket... may says thats a C2 because the MCB size is wrong for the 2.5

 

[ProDave]

see similar all the time... 32a ring with a spur from the MCB, perfectly fine... remove the ring and have just the 2.5 feeding a socket... may says thats a C2 because the MCB size is wrong for the 2.5

And that in a nutshell is how daft the regs can be. and where a 20 or 25A mch can be handy.

 

[Andy™]

And that in a nutshell is how daft the regs can be. and where a 20 or 25A mch can be handy.

its not how daft the regs can be imo, its the 'electricians' who cant think for themselves if anything is different from 'normal'

perfectly compliant, fault protection by the MCB, overload by the fact its one point.(yes, i know it could in theory have 2x plug with 13a loads, but still the same situation as a spur from a ring)

 

[binky]

perfectly compliant, fault protection by the MCB, overload by the fact its one point.(yes, i know it could in theory have 2x plug with 13a loads, but still the same situation as a spur from a ring)

Totally agree