6.3.3??

[JohnW2]

wouldn't even be compliant with BS7671 unless you could justify a belief that 6A was an appropriate design current for the circuit

Then it would. Belief and appropriate are not the right words if the design current were 6A.

As I say so often, socket circuits must be the designer's biggest nightmare, because they preclude a proper design process - one really does need some sort of (hopefully reasonably well-informed and sensible) 'crystal ball' - that's why I have to use words like 'belief' and 'appropriate'.

Would the main argument not be that too large a cable had been used? Although, again this would be extra safe and not non-compliant.

Who's 'main argument'? Certainly not mine - as I've just written, I can't see that having a cable which is larger than required for CCC or VD, or larger than the OPD's In is ever going to be a problem in terms of compliance. If termination were possible (which it clearly wouldn't be), a 10mm² or 16mm² RFC (with a 32A MCB) would be perfectly compliant.

This is even more hypothetical than usual as we, or at least I, have no idea what the OP has in mind.

It may be hypothetical in terms of this thread but, more generally, I have seen people try to 'cheat' by specifying an unrealistically/ unreasonably low design current for a circuit - haven't you?

Kind Regards, John.

 

[sparkticus]

The only way (as far as I know) to make a 6amp OCPD connected to 2.5mm twin+earth compliant is :

A single 3 or 5 amp lighting socket (the round pin ones) as the only "socket" on the circuit.

or

A fixed appliance hard wired.

or

A lighting circuit



With that said the 2.5 t&e radial could then be used for VD requirements.

 

[JohnW2]

My main point around that is that whilst a designer has to justify his circuit design, I would be surprised if he had to justify picking a 6A design requirement and if in that position would strongly argue the point.

That surely depends upon how competent and sensible the designer is, doesn't it? To take an extreme example, what if I told you that the circuit in question, for which the designer had specified a 6A 'design current'. was supplying 5 double 13A sockets in a kitchen?

Kind Regards, John.

 

[westie101]

True, but I'm coming from the POV that the designer knows what he is talking about, in your case the whole design would be suspect!

 

[EFLImpudence]

So, if we assume (never assume) that the circuit is a 2.5mm² Ring FC (RFC stands for Radial FC as well) which is obviously supplying socket-outlets then have we come to the conclusion that RFLighting is correct and that 32A is both the maximum and minimum rating for the CPD?

 

[westie101]

However, BS7671 does impose requirements on the design process. Specifically, it requires than the In of the OPD shall not be greater than the 'design current' of the circuit - and that is defined (something like) the total current that the designer believes is likely to ever be demanded.

That is as I see it, the circuit has to be designed to carry the load the designer decides upon.

If the designer cannot demonstrate that the design current is 'reasonable' (per that definition), and below In of the OPD, then that cuircuit will not be compliant with BS7671.

Is that contained within BS7671?
As long as the design complies with the former, the issue of specifying too low a load is more contractual between the designer and the client!

 

[westie101]

conclusion that RFLighting is correct and that 32A is both the maximum and minimum rating for the CPD?

My view is that 32A is probably the maximum but the minimum is what the designer specifies below that figure

 

[JohnW2]

The only way (as far as I know) to make a 6amp OCPD connected to 2.5mm twin+earth compliant is :
A single 3 or 5 amp lighting socket (the round pin ones) as the only "socket" on the circuit.
or A fixed appliance hard wired.
or A lighting circuit

Well, they are certainly all fairly clear-cut situations - but, as I suggested,I think a designer can probably use judgement in other situations in which the maimum demand can reasonably be predicted. Imagine, say, a circuit supplying an appreciable number of sockets (13A, 5A or 3A) high on the walls of an art gallery, with the specific purpose of making provision for very low wattage light fittings, as required. I don't think I would have a problem specifying (or justifying) a 6A design current, would you? (even though people with ladders could plug electric kettles into them if they were 13A sockets!).

Kind Regards, John.

 

[JohnW2]

True, but I'm coming from the POV that the designer knows what he is talking about, in your case the whole design would be suspect!

Yes, but that's why we have rules and regulations. If the assumption were that everyone would 'do the right thing', anywy, there would be no need for rules.

Kind Regards, John.

 

[EFLImpudence]

However, BS7671 does impose requirements on the design process. Specifically, it requires than the In of the OPD shall not be greater than the 'design current' of the circuit - and that is defined (something like) the total current that the designer believes is likely to ever be demanded.

Important typo - not should be deleted.

 

[Wontdothatagain]

Imagine, say, a circuit supplying an appreciable number of sockets (13A, 5A or 3A) high on the walls of an art gallery, with the specific purpose of making provision for very low wattage light fittings, as required. I don't think I would have a problem specifying (or justifying) a 6A design current, would you? (even though people with ladders could plug electric kettles into them if they were 13A sockets!)quote]

The problem there is future use, the designer has to take into account that the property may change hands and be converted into say a night club and those same sockets could be used to power some high wattage jiggley lights.

 

[JohnW2]

So, if we assume (never assume) that the circuit is a 2.5mm² Ring FC (RFC stands for Radial FC as well) which is obviously supplying socket-outlets then have we come to the conclusion that RFLighting is correct and that 32A is both the maximum and minimum rating for the CPD?

I think that is true unless the designer can produce a good argument that the maximum demand, hence design current and minimum MCB In, is unlikely to ever exceed some figure which is less than 32A - and I'm suggesting that, with multiple 13A outlets, that may often be a difficult argument to mount (unless there are very special circumstances applying)

Kind Regards, John

 

[JohnW2]

However, BS7671 does impose requirements on the design process. Specifically, it requires than the In of the OPD shall not be greater than the 'design current' of the circuit - and that is defined (something like) the total current that the designer believes is likely to ever be demanded.

Important typo - not should be deleted.

Whoops again You know what I meant - original has been corrected!

Kind Regards,John.

 

[westie101]

I work a lot with HSE Codes of Practice and show others how they can comply with them.
The particular area is electrical and is known to cause a number of deaths every year from non compliance. The advice starts with this statement

This guidance is issued by the Health and Safety Executive. Following the guidance is not compulsory and you are free to take other action. But if you do follow the guidance you will normally be doing enough to comply with the law. Health and safety inspectors seek to secure compliance with the law and may refer to this guidance as illustrating good practice

Within it there are few specifics but lots of options, sometimes for a particular case there is no actual guidance. If it was followed to the letter these jobs could not be done, so what do I do?
Agree a design and method that complies with the legal requirements (yes it can be on my head if it goes wrong) as with wiring installations that is what a designer should do!
In other cases we agree on precautions that are far more than the minimum (sometimes because I specify that the minimum is not acceptable)

Any CoP generally specifies the minimum requirements not the maximum (apart from current carrying capacity)

 

[sparkticus]

Imagine, say, a circuit supplying an appreciable number of sockets (13A, 5A or 3A) high on the walls of an art gallery, with the specific purpose of making provision for very low wattage light fittings, as required. I don't think I would have a problem specifying (or justifying) a 6A design current, would you? (even though people with ladders could plug electric kettles into them if they were 13A sockets!).

I think that is a "reasonable" design criteria and I have designed and installed such circuits myself in commercial/industrial establishments. As far as I know you could also protect a socket outlet with a 6amp OCPD if it is under the supervision of an (instructed person) for example in a lab where the particular circuit in on a limited output UPS and where the Ib is < 6 amps.

I can't tell you right now where it is in the regs (if at all in the way I write the following) but my interpretation of such a situation (6amp MCB on a 2.5mm radial) is that it does not comply with BS7671 only if the expected/possible loading is > 6 amps which in reality takes us into socket outlets in easily accessible locations. In other words if circuit disconnection occurs due to loads that fall within the "expected" capability of a service outlet (a 13 amp socket disconnecting at 7/8 amps etc) then that does not comply with BS7671.