socket

[Buzz-light-bulb]

Little scenario for you all.

I've been doing an eicr today and come across a double socket wired as a radial on a 2.5mm t-e, which is protected by a 32 amp rcbo.
Technically this cannot overload as the cable can withstand 27 amp ref method c. Unless mr DIY comes along and starts adding new sockets which I am not responsible for so my question is would you leave it

 

[Hawkmoon]

Yes no code - no different to spur on rfc wired from mcb.

 

[Buzz-light-bulb]

Yes no code - no different to spur on rfc wired from mcb.

That's what I thought

 

[Pete999]

Tin hat on, but I would change the cb for a 20a to comply, 20a radial 2.5 32a radial 4.0mm, only saying, section 15 I think Regs at work I'm having a nice bottle of wine,

 

[telectrix]

might be worth a comment on the eicr....... recommend 20A RCBO to allow for possible additions.

 

[NickD]

Little scenario for you all.

I've been doing an eicr today and come across a double socket wired as a radial on a 2.5mm t-e, which is protected by a 32 amp rcbo.
Technically this cannot overload as the cable can withstand 27 amp ref method c. Unless mr DIY comes along and starts adding new sockets which I am not responsible for so my question is would you leave it

It doesn't quite meet correct coordination as In > Iz which makes it vulnerable to a subsequent alteration overloading the cable. If it was risk-averse little me I think I'd put it down as a C3 just to cover my backside; there is after all scope for an improvement, i.e. fit a 25A RCBO. Obviously it's safe as it stands.

 

[Pete999]

It doesn't quite meet correct coordination as In > Iz which makes it vulnerable to a subsequent alteration overloading the cable. If it was risk-averse little me I think I'd put it down as a C3 just to cover my backside; there is after all scope for an improvement, i.e. fit a 25A RCBO. Obviously it's safe as it stands.

Can't quite understand your reasoning for fitting a25a RCBO

 

[uksparks]

Id mention about changing it to a 20A as that's best practise.

 

[NickD]

Think about what happens if someone upgrades the double socket to an (unfused) triple socket with the circuit as it stands and plugs in three 3kW heaters.

 

[NickD]

Three 2.4kW heaters. Sorry.

 

[Pete999]

Think about what happens if someone upgrades the double socket to an (unfused) triple socket with the circuit as it stands and plugs in three 3kW heaters.

That's my point a radial wired in 2.5 should be protected by a 20a cb

 

[NickD]

That's my point a radial wired in 2.5 should be protected by a 20a cb

But then you might get false tripping. That cable can (we are told) take 27A and there is a double socket that one might reasonably want to plug two 2.8kW heaters into. The cable will take this, and with a 25A OCPD all will be well. On a 20A, it will trip (eventually) even though the cable was never at risk.

 

[NickD]

(You don't want to recommend an 'improvement' on an EICR that's going to make the installation more proof against bodgery in the future, but in the present may infuriate the user with false tripping introduced to an installation that was perfectly safe as it was in its present state.)

 

[GLENNSPARK]

might be worth a comment on the eicr....... recommend 20A RCBO to allow for possible additions.

what for?...

it were good as found.....

we all know that a condition report is good for the condition as it was inspected & tested...no more-no less...

if a turnip wants to arse about adding stuff then thats their problem...

note that its there by all means...but not 20A RCBO stuff...

 

[Geoffsd]

Are there any unfused triple sockets?

The cable is protected from overload by the plug fuse(s) and fault current by the mcb.

If anyone adds more sockets they are incompetent.

 

[Hawkmoon]

Your reasons for coding it should also then apply to any spur off an rfc...If you won't code that, then why code this??

It's no different - you can't code depending on what some numpty may do in the future.

I wouldn't even comment on EICR

 

[GLENNSPARK]

It doesn't quite meet correct coordination as In > Iz which makes it vulnerable to a subsequent alteration overloading the cable. If it was risk-averse little me I think I'd put it down as a C3 just to cover my backside; there is after all scope for an improvement, i.e. fit a 25A RCBO. Obviously it's safe as it stands.

total crap.

 

[Pete999]

total crap.

Say it like it is Glenn

 

[NickD]

Your reasons for coding it should also then apply to any spur off an rfc...If you won't code that, then why code this??

It's no different - you can't code depending on what some numpty may do in the future.

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.

 

[7029 dave]

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.

Totally agree with your comment.

 

[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!

 

[Badged01]

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

And you're technical justification for that in-line with regulations would be .......

 

[Colin33]

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.

I certainly wouldn't advocate the scenario, and have always worked on the basis of MCB egual or less than CCC of cable. I have always replaced 'offending' MCB's in the past with something more 'suitable' but maybe I've been over cautious? I don't get involved with EICR's so don't have the dilemma of which code is 'appropriate'

 

[jamie-spark]

See 433.1.103

 

[Hawkmoon]

Say it like it is Glenn

Yes, because it is total crap!! lol

 

[Hawkmoon]

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

Explain to me where/how it does not comply...

 

[Hawkmoon]

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.....

Overload protection does not have to be at the origin of the circuit...

 

[NickD]

Yes, because it is total crap!! lol

But with an ickle maggot of truth wiggling about in it.

 

[jaypp]

deleted.

 

[Hawkmoon]

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, because even though, in your example, overload considerations may be met (though doubtful), thermal constraints (cpc fault current) certainly are not.

 

[dazza1981]

Overload protection does not have to be at the origin of the circuit...

So you think its ok to have a 1.5mm cable protected by a 50 amp breaker???