socket

[Hawkmoon]

The difference is there's nothing you can do with the spur on the RFC because the ring is inherently vulnerable to this no matter what you do. It is perfectly correct in all design aspects so no code or comment. The 27A cable on a 32A OCPD does not meet correct co-ordination in terms of the upstream OCPD, instead relying on downstream fusing of the 2x13A which is relatively unusual in domestic, where bodgery is rife, and I believe we are under some degree of responsibility to guard against it (if it's not domestic I'd be less worried). I'm risk averse. I'd C3 it. Others may not. I wouldn't particularly choose to decry their choice.

It makes no difference what is usual/unusual in domestic - you look at/determine an install on its compliance re: BS7671 - if the cable (in this instance) has overload protection and satisfies thermal constraints then what reason would you have to comment/code it??? Seems you are being influenced by domestic installation convention.

You need to forget what is the apparent 'norm' for 'domestic installations' and apply regs as you would any install comm/ind/dom.

As I say...no code...no comment on EICR...All good!

 

[Pete999]

It makes no difference what is usual/unusual in domestic - you look at/determine an install on its compliance re: BS7671 - if the cable (in this instance) has overload protection and satisfies thermal constraints then what reason would you have to comment/code it??? Seems you are being influenced by domestic installation convention.

You need to forget what is the apparent 'norm' for 'domestic installations' and apply regs as you would any install comm/ind/dom.

As I say...no code...no comment on EICR...All good!

Well in this case it clearly doesn't comply. does it? if we don't comply then it's the slippery slope to butchery

 

[Colin33]

I've always thought that the sole purpose of the Fuse/MCB was to protect the cable ie the MCB needs to be equal to or less than the maximum current carrying capacity of the cable. So in this case, the 32A MCB is not suitable.....

 

[NickD]

As I say...no code...no comment on EICR...All good!

Having reminded myself that a C3 means improvement required, I now agree, no code is appropriate. I would say maybe a comment but I don't think the EICR form lends itself well to comments that aren't tied to codes (observations section requires a code for any observation made). Amazing what you can learn from civilised discussion. Cheers.

 

[HappyHippyDad]

I've always thought that the sole purpose of the Fuse/MCB was to protect the cable ie the MCB needs to be equal to or less than the maximum current carrying capacity of the cable. So in this case, the 32A MCB is not suitable.....

The purpose of the MCB is to protect the cable and as long as the Zs is ok then it is protecting against fault current. Its not protecting against overcurrent though, however the fuse in the plug is. Saying that I agree with Nick and Dave, although I wouldn't code it as a C3 because it does meet the regs (its just the same as taking a spur from a ring which is protected by a 32A MCB) but I would suggest to the customer I fit a 20A RCBO, I'd explain why and let them make the choice, or at the very least tell them not to add any DIY spurs on to it.

 

[gazj82]

I've always thought that the sole purpose of the Fuse/MCB was to protect the cable ie the MCB needs to be equal to or less than the maximum current carrying capacity of the cable. So in this case, the 32A MCB is not suitable.....

The fuses in the plug tops will stop an overload on the cable. This is no different to tapping of a busbar chamber (industrial) in smaller tails and having a switch fuse inline after a meter or 2 of cable. Protection against over load does not always have to be at the source of the circuit.

 

[Buzz-light-bulb]

This is the problem with this electrical game there's never a definitive answer this is why so many electricians get confused, suppose at the end of the day ( is the beginning of the night) it boils down to basic common sense.

 

[gazj82]

Although I stand by what I said above, someone could possibly use an unfused double adaptor, how do they still get away with selling them!

 

[NickD]

Although I stand by what I said above, someone could possibly use an unfused double adaptor, how do they still get away with selling them!

This is why I think it's important to remember what you're assessing and the real-world factors, whether it's a plating plant, a pigfarm or a house. Hot dip baths, pig crap and DIY Dans each present their own challenge to be mitigated against.

 

[nickblake]

Where in the regs does it say you can wire a 2.5mm twin and earth and protect it with a 32 amp mcb you can with an additional fused spur as well as 1.5mm protective device for 2.5mm twin and earth is as stated in the little green book is 20 amp which is an A3 radial ,there is a risk of potential over load , how longs the cable length one bit of insulation will de rate the whole cable I would quite happily put it down as a C2 ,there are so many unfused 3 way adaptors out there i wouldn't risk it

 

[Colin33]

The fuses in the plug tops will stop an overload on the cable. This is no different to tapping of a busbar chamber (industrial) in smaller tails and having a switch fuse inline after a meter or 2 of cable. Protection against over load does not always have to be at the source of the circuit.

So based on this assumption I could wire a single 13A socket on the end of some 1mm cable from a 50A MCB in the CU?

 

[Pete999]

To protect our customers, as well as ourselves, we have to comply with BS 7671, the regulations for final socket circuits are there for us all to see. Should we detract from these regulations then we are in dispute with the EAW and in the eyes of the law, we are breaking this Act. If we install socket outlets in line with BS 7671 then, surely we are complying with the current regulations, until someone tells me different, then I will install 13amp socket outlets, in compliance with BS7671, 20amp radials with 2.5mm, 32 amp radials with 4mm and Ring Final circuits 32 amp with 2.5mm

 

[HappyHippyDad]

Where in the regs does it say you can wire a 2.5mm twin and earth and protect it with a 32 amp mcb you can with an additional fused spur as well as 1.5mm protective device for 2.5mm twin and earth is as stated in the little green book is 20 amp which is an A3 radial ,there is a risk of potential over load , how longs the cable length one bit of insulation will de rate the whole cable I would quite happily put it down as a C2 ,there are so many unfused 3 way adaptors out there i wouldn't risk it

Page 425, Appendix 15 Fig 15A

"An unfused spur may be connected to the origin of the circuit in the distribution board" with regard to connecting one (2.5mm) spur at the CU from the 32A MCB of the ring.

I feel like I'm arguing against the case for doing anything now! I'm not, I dont like it and I'd tell the customer so, but its not breaking the regs.

 

[Plonker 3]

Reg 434.2.1 could be applied here.

 

[NickD]

I will install 13amp socket outlets, in compliance with BS7671, 20amp radials with 2.5mm, 32 amp radials with 4mm and Ring Final circuits 32 amp with 2.5mm

Where in 7671 does it mandate that?

 

[HappyHippyDad]

So based on this assumption I could wire a single 13A socket on the end of some 1mm cable from a 50A MCB in the CU?

I think its a good idea to show extremes when getting your point across XT but... you are just looking at overcurrent with the above example not fault current, also it would be completely unrecognised by electricians and therefore far more likely to cause problems and also its against the regs, whereas one 2.5mm spur from the origin would be ok for fault current, fairly recognised and adhere to the regs.

But!! If it was just a 2.5mm coming out of a 32A MCB with no ring then why not advise the housholder to change to a 20A MCB, you dont have to but it seems like a good idea.

 

[Badged01]

So based on this assumption I could wire a single 13A socket on the end of some 1mm cable from a 50A MCB in the CU?

No, no, no! Minimum cable size for power circuit is 1.5mm but yes a single 13A socket on a 50A MCB in 1.5mm could be done. (433 & 434 give details of how & why!) Whether you'd want to do it is perhaps another thought ....

 

[HappyHippyDad]

Reg 434.2.1 could be applied here.

That is a bit contradictory to Fig 15A isn't it!! The only thing I can say to that is reg 433.2.1 doesn't have to be met if Reg 433.2.2 applies, but it doesn't look like it does!

The only other defense I can use is Fig 15A is extremely clear in its acceptance for a spur from the MCB, whereas the reg you have quoted is not as specific.

 

[7029 dave]

No, no, no! Minimum cable size for power circuit is 1.5mm but yes a single 13A socket on a 50A MCB in 1.5mm could be done. (433 & 434 give details of how & why!) Whether you'd want to do it is perhaps another thought ....

You would not be doing it in my house or any of my jobs, straight out of the door tools first.......!!

 

[Badged01]

Appendix 15 is informative and just sets out a possible option for a solution to 433 ...... there are other ways to skin the cat by careful reading and interpretation of the regs!