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

[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. ?

its to do with the current carrying capacity of the 2.5 T&E (17-27amps) , the mcb is there to protect the cable not the load ( but you known that all ready) that is why you should not use a 32A mcb on a radial circuit ( but again you know this)

 

[Andy™]

its to do with the current carrying capacity of the 2.5 T&E (17-27amps) , the mcb is there to protect the cable not the load ( but you known that all ready) that is why you should not use a 32A mcb on a radial circuit ( but again you know this)

wrong. even the diagram in appendix 15 shows 2.5 used on a 32a radial (only to one point though, but fact still remains that 2,5mm can be used on a 32a circuit)

 

[Sharpend]

wrong. even the diagram in appendix 15 shows 2.5 used on a 32a radial (only to one point though, but fact still remains that 2,5mm can be used on a 32a circuit)

But surely that makes a mockery of having the mcb protect the cable? 
I guess if you can guarantee that the load will never exceed the cable carrying capacity then ??? Is it right or is it wrong??

 

[kerching]

wrong. even the diagram in appendix 15 shows 2.5 used on a 32a radial (only to one point though, but fact still remains that 2,5mm can be used on a 32a circuit)

f

 

[Andy™]

But surely that makes a mockery of having the mcb protect the cable? 
I guess if you can guarantee that the load will never exceed the cable carrying capacity then ??? Is it right or is it wrong??

not really. overload and fault protection are 2 different things. if, by nature of the load, if the circuit canot be overloaded then overload protection doesnt need to be by the MCB, you only need to provide fault protection, which in almost all cases, 32a MCB will protect a 2.5mm t&e

which is why you can take a 2.5mm spur form a ring / 32a radial to one point, as the max load possible is 13a (yes, i know a double socket could have 2x 13a loads, but regs still consider it one point of 13a...)

so how many of you dont agree with a 2.5mm cable from a 32a MCB, but also dont have an issue with a spur from a ring? whats the difference?

 

[Sharpend]

not really. overload and fault protection are 2 different things. if, by nature of the load, if the circuit canot be overloaded then overload protection doesnt need to be by the MCB, you only need to provide fault protection, which in almost all cases, 32a MCB will protect a 2.5mm t&e

which is why you can take a 2.5mm spur form a ring / 32a radial to one point, as the max load possible is 13a (yes, i know a double socket could have 2x 13a loads, but regs still consider it one point of 13a...)

so how many of you dont agree with a 2.5mm cable from a 32a MCB, but also dont have an issue with a spur from a ring? whats the difference?

I agree that we can design a circuit whereby the cable is never going to be overloaded as such and therefore overload protection is not required but is it strictly correct or is it a deviation from standard design method? 
 

regarding the ring circuit we are led to believe it is possible as the Circuit is balanced— whilst we know in reality this is rarely the case. TBF my grey matter hasn’t been used on Electrics much recently everybody else is wearing it out on other junk! So I may be corrected. 

 

[Andy™]

I agree that we can design a circuit whereby the cable is never going to be overloaded as such and therefore overload protection is not required but is it strictly correct or is it a deviation from standard design method? 
 

regarding the ring circuit we are led to believe it is possible as the Circuit is balanced— whilst we know in reality this is rarely the case. TBF my grey matter hasn’t been used on Electrics much recently everybody else is wearing it out on other junk! So I may be corrected. 

433.3.1(ii)

ring or radial is irrelevant - the 2.5mm spur is still 2.5mm. the cable as part of the ring is required to carry 20a, but that doesnt apply to the spur wiring

 

[Fleeting]

The biggest failure to this scenario is that the OP refers to a ring final then suggests a situation which is not a ring final but a radial as suggested in 15B Appendix 15 therefore non compliant. However Appendix 15 is informative and not a cast in stone Regulation so he/she must offer an argument conversant with BS7671 for a non fixed load.

 

[SPECIAL LOCATION]

The biggest failure to this scenario is that the OP refers to a ring final then suggests a situation which is not a ring final but a radial as suggested in 15B Appendix 15 therefore non compliant. However Appendix 15 is informative and not a cast in stone Regulation so he/she must offer an argument conversant with BS7671 for a non fixed load.

So as the OP...

Lets suggest a "very very small ring"..

MCB  0.5m of 2.5mm T&E supplying 1x single socket, returning back via another 0.5m of 2.5mm T&E...

If you could branch some 2.5mm radial spurs off the socket terminations...

Could you also branch one or more 2.5mm radials off the MCB terminations..?

If yes... how many?

As..  at the end of the day the load on each individual leg would be limited by the 13A socket outlets protective device..

:C

 

[Andy™]

Could you also branch one or more 2.5mm radials off the MCB terminations..?

appendix15 says yes

 

[poni]

so how many of you dont agree with a 2.5mm cable from a 32a MCB, but also dont have an issue with a spur from a ring? whats the difference?

Well,I don't know whether to stand up or sit down, I am all a dither now, you are correct, but I would never think about doing that on a radial circuit, and I forgot the fact, because I don't do does not make it wrong,  

 

[SPECIAL LOCATION]

Well,I don't know whether to stand up or sit down, I am all a dither now, you are correct, but I would never think about doing that on a radial circuit, and I forgot the fact, because I don't do does not make it wrong,  

Which all just goes to show the elements of overlap between...

Compliance with BS7671 guidance..

Electrical safety..

Common sense..

Good Practice.. 

Interpretation and/or deviation from BS7671..

How much you could push the boundaries if you wanted to..

etc..

etc..

Best thing to do is..  Stand up..  Sit down..  have a beer  Guinness

Sit down again, turn around, stand up have another beer   Guinness

This all just goes to show what can happen when your mind starts drifting on auto-pilot..

Guinness

When I click my fingers all will be returned back to normal design/installation/testing..

wot we all do normally.. every day..  

:C