Ring Finals Vs Radials

[JohnW2]

Is there anything stopping someone selling a socket which cannot tolerate more than 20A on the cable?

Good question. There's a general requirement: "Socket-outlets shall be so designed and constructed that in normal use their performance is reliable and without danger to the user or to the surroundings". Given that "normal use" when the standard was written meant in the context of a 30A ring final, I think that would cover it. However BS 1363 doesn't refer to BS 7671 or to the (then) IEE Wiring Regs.

Interesting questions - but is it probably not really about physical terminal capacity, what testing is done and what 'current rating' (if any) is claimed for the terminals, rather than a question of what current the terminals 'can tolerate'? I would imagine that it would be quite difficult to design a screw terminal which could satisfactorily accommodate the conductors concerned which was not able to 'tolerate' 32A, probably appreciably more, flowing between the terminated conductors, wouldn't it?

Kind Regards, John.

 

[stillp]

I would imagine that it would be quite difficult to design a screw terminal which could satisfactorily accommodate the conductors concerned which was not able to 'tolerate' 32A, probably appreciably more, flowing between the terminated conductors, wouldn't it?

If the conductors were terminated in a single terminal then I'd imagine the only way the terminal would be unable to tolerate 32A in the conductors would be if said terminal was made of something with a low melting point.
However there were once (are they still available?) twin socket-outlets with duplicated L, N, and E terminals, so that the T & E entering the SO was on one side, and the T & E leaving the SO on the other, so the current in the RFC flowed through 2 brass terminals riveted to a plated steel strip. Lots of opportunity for one or both of those riveted connections to fail.

 

[JohnW2]

If the conductors were terminated in a single terminal then I'd imagine the only way the terminal would be unable to tolerate 32A in the conductors would be if said terminal was made of something with a low melting point.

I certainly can't think of any other mechanism, and I'm doubtful about even that one - if the conductors terminated in a single terminal (or the connection between them) got hot enough to melt, or even damage, anything, then surely something would be very wrong?

IfHowever there were once (are they still available?) twin socket-outlets with duplicated L, N, and E terminals, so that the T & E entering the SO was on one side, and the T & E leaving the SO on the other, so the current in the RFC flowed through 2 brass terminals riveted to a plated steel strip. Lots of opportunity for one or both of those riveted connections to fail.

Yes, I'd forgotten about those and was, as you probably realised, talking about single terminals. However, having said that, I'm not sure that what you say should affect the 'rating' of the socket - which surely would be based on the per-spec product when manufactured, not what might happen if a rivited connection subsequently failed in service?

Kind Regards, John.

 

[stillp]

Yes to both, but you were suggesting it would be difficult to design a terminal that couldn't carry the necessary current, so I gave you 2 examples of how to do it.
Why you'd want to is another matter...

 

[ebee]

Does BS 1363 specifically list terminals as being capable of accepting 2 x 4.0mm plus 1 x 2.5 conductor as per the 4.0 T & E radial with 2.5 T & E spurs as per our reg book ?

If not then what`s to preclude a 4.0 "lollipop" or even a 6.0 "lollipop" or even a chimley sweeps brush providing there is room in the terminals? Some do have lots of room!

(For lollipop imagine a cooker unit decommissioned and used as the source of a ring ie = radial with ring on end and for "Chimney sweep brush" imagine 3 or 4 or more spurs fed from the end of the radial portion)

see Electrics can be fun

Similarly what its to stop us having two rings or more, both having each leg connected by the same fuseway providing that the designer declares it not as two ring final circuits but as one final circuit consisting of two rings.

Daft innit?

 

[stillp]

"Line and neutral terminals in fixed socket-outlets shall permit the connection, without special preparation, of one, two or three 2.5 mm2 solid or stranded or of one or two 4 mm2 stranded conductors"

 

[ebee]

I thought (from Memory) that so it does not list as a 4.0 radial with a 2.5 spur but the regs book "suggests" it. Therefore, by inference, we ourselves might suggest other combinations too as long as the terminals accept them I would think.

 

[stillp]

The text I quoted from BS 1363-2 is perhaps more interesting for what it does not say. For example, it doesn't require the terminals to be capable of securely connecting to a single 1.5 mm2 conductor. Or a single 6 mm2.

 

[ebee]

Another one I think would look daft is a tree circuit.
a 16A or 20A fuseway feeding a socket, two radials from socket to two more, doubling everytime, in fact two such radials or even three from said fuseway.

It`s the old established tree circuit but a bit of a beggar to I & T though.

I must have a warped mind to think of these things!

 

[EFLImpudence]

That's certainly one problem and another, certainly for mere amateurs, is that I'm sure that trying to play 6mm² within standard backboxes would feel more like plumbing than electrical installation, and a complete pain - 4mm² is bad enough!

Is that necessarily a reason to eschew the design if it's the most appropriate?

No - but I didn't say it was. I do, however, seriously doubt that even a professional would normally contemplate wiring sockets in 6mm² - and, as has already been said, that would limit one to a non-branching radial circuit, because of consderations of terminal capacity (even with MK).

Even if, for a 32A radial, it were necessary to use 6mm² from the CU because of the installation method that does not mean it needs to be continued 'around the kitchen' (or wherever).

Three 4mm² conductors are quite easily connected to sockets in my experience.


Edit - Sorry if I have repeated - I didn't realise there was another page.

 

[JohnW2]

Yes to both, but you were suggesting it would be difficult to design a terminal that couldn't carry the necessary current, so I gave you 2 examples of how to do it. Why you'd want to is another matter...

Hmmm - I do love people who take my words that literally In any event, whilst I accept your 'low melting point terminal' as one way one could design such an animal, I'm not so sure about your second example, since one would surely not design a product which deliberately had faulty riveted connections at the time of manufacture?

Kind Regards, John.

 

[JohnW2]

Even if, for a 32A radial, it were necessary to use 6mm² from the CU because of the installation method that does not mean it needs to be continued 'around the kitchen' (or wherever).

True, one would obviously only need 6mm² for those bits of cable whose installation method required it - whichever bits they may be.

Kind Regards, John.

 

[stillp]

Yes to both, but you were suggesting it would be difficult to design a terminal that couldn't carry the necessary current, so I gave you 2 examples of how to do it. Why you'd want to is another matter...

Hmmm - I do love people who take my words that literally In any event, whilst I accept your 'low melting point terminal' as one way one could design such an animal, I'm not so sure about your second example, since one would surely not design a product which deliberately had faulty riveted connections at the time of manufacture?

Kind Regards, John.

Probably not, but it would be quite an easy design mistake to make, if you didn't know the likely temperature rise of the conductors in the first place, and the reliability of riveted connections in the second. I once worked for a manufacturer of switches for automotive applications, who made several thousand headlamp switches that depended on a rivet holding two copper strips, one on each side of a piece of thermoplastic. Fine until the switch was carrying full load, in a hot climate, then the plastic softened slightly, the pressure came off the rivetted joint, whose resistance promptly increased, which made the switch overheat...

 

[JohnW2]

Probably not, but it would be quite an easy design mistake to make, if you didn't know the likely temperature rise of the conductors in the first place, and the reliability of riveted connections in the second. I once worked for a manufacturer of switches for automotive applications, who made several thousand headlamp switches that depended on a rivet holding two copper strips, one on each side of a piece of thermoplastic. Fine until the switch was carrying full load, in a hot climate, then the plastic softened slightly, the pressure came off the rivetted joint, whose resistance promptly increased, which made the switch overheat...

True - but, as I'm sure you realise, my point was that, unless one were an idiot, one would not deliberately design a product to behave in such a way

Kind Regards, John.

 

[JohnW2]

I thought (from Memory) that so it does not list as a 4.0 radial with a 2.5 spur but the regs book "suggests" it. Therefore, by inference, we ourselves might suggest other combinations too as long as the terminals accept them I would think.

I guess that depends upon what mean by 'list' and 'suggest'. Appendix 15 of the BGB does include it. Although that Apendix is only 'informative', it is also, to the best of my knowledge, also the only place where other things we regard as 'compliant' (or not)(e.g. only having one socket supplied by a 2.5mm² unfused spur) are explicitly mentioned.

Kind Regards, John.