Multiple conductors in terminals - installation method

[JohnW2]

Surely then, that is not mechanically, and therefore not electrically, secure.

You're getting semantic! The point is that the joint should be electrically and mechanically secured when made, and would remain such 'if not disturbed'. The solder (or resin, or tape, or whatever) simply prevents that 'secure' state being disturbed - just as with my rope/tape analogy.

Kind Regards, John.

 

[JohnW2]

No cut & clench pliers then John?

New fangled gadgets

Kind Regards, John.

 

[EFLImpudence]

Have you looked at any of the devices in a CU recently (MCBs, RCDs, RCBOs, Main Switches etc.)?

Oh yes, but I thought we were talking about sockets and switches etc.

Yesterday removed a 10mm² conductor from an mcb and all the strands were in a line - just right.

 

[JohnW2]

Oh yes, but I thought we were talking about sockets and switches etc.

We essentially were, but the principle is the same, and I imagine modern 'things in a CU' wouldn't have terminals such as they do if 'screwing into the wire' was regarded as satisfactory,would they?

Yesterday removed a 10mm² conductor from an mcb and all the strands were in a line - just right.

Indeed, that's how it should be, but I'd personally always 'flatten' the strands first to ensure that happened, wouldn't you? Putting the stranded cable into the terminal 'as is' and relying on the brute force of tightening the screw to do the necessary 're-arranging of strands' satisfactorily sounds all very iffy to me.

Kind Regards, John.

 

[EFLImpudence]

Yesterday removed a 10mm² conductor from an mcb and all the strands were in a line - just right.

Indeed, that's how it should be, but I'd personally always 'flatten' the strands first to ensure that happened, wouldn't you? Putting the stranded cable into the terminal 'as is' and relying on the brute force of tightening the screw to do the necessary 're-arranging of strands' satisfactorily sounds all very iffy to me.

Yes, but the point was that would be impossible with a screw terminal.

 

[Paul_C]

Anyway, to put this all in perspective, of all the shapes and sizes of cables, solid conductors are only encountered in (some) 1, 1.5 and 2.5mm² ones. I still wonder why that happened with the change to metric - do you think it was just a matter of manufacturing cost? Is it the same in other countries? (where's Paul? )

Somebody call?

North American Romex (the equivalent of "T&E") is generally solid cores in the #14 and #12 AWG sizes, then stranded for #10 and larger. Approximate metric-equivalent sizes:

#14 = 2.08 sq. mm
#12 = 3.31 sq. mm
#10 = 5.26 sq. mm

As with 1.5 & 2.5 sq. mm here, however, the smaller sizes are available as both solid and stranded versions in singles.

Conversely, I believe that the Australian version of 2.5 sq. mm T&E has stranded conductors.

 

[JohnW2]

[Yes, but the point was that would be impossible with a screw terminal.

Oh, sure - screwing directly into/onto conductors is a pretty iffy concept. I may be wrong, but I'm pretty sure that I have seen sockets and other accessories which have 'proper' terminals - or did I dream it?

Kind Regards, John.

 

[JohnW2]

Anyway, to put this all in perspective, of all the shapes and sizes of cables, solid conductors are only encountered in (some) 1, 1.5 and 2.5mm² ones. I still wonder why that happened with the change to metric - do you think it was just a matter of manufacturing cost? Is it the same in other countries? (where's Paul? )

Somebody call? North American Romex (the equivalent of "T&E") is generally solid cores in the #14 and #12 AWG sizes, then stranded for #10 and larger.

OK, so much the same as here - so what's your view of the reason?

Kind Regards, John.

 

[ban-all-sheds]

[sorted]Wire everything with tri-rated singles in flexible conduit.[/sorted]


Thinking of that - does the French gaines system use stranded cables? I assume it does.

I know you can get bootlace crimpers which make a half-round cross section - can you get triangular so that you could arrange 3 conductors in a trefoil?

 

[Paul_C]

OK, so much the same as here - so what's your view of the reason?

I'm not sure what particular reason, if any, was ever given for the change to solid conductors with the change to metric sizes. Ditto for the change at the same time to bare copper in place of tinned copper.

One point of note on the comparison between British and American connections is that traditionally the 15 & 20A receptacles and switches used extensively with #14 & #12 cable in North America have screw terminals where the conductor is looped around under the head instead of the type employed on British sockets and light switches, making solid conductors ideally suited to the task (and also making it a case of "one conductor per terminal" by that method).

 

[JohnW2]

I'm not sure what particular reason, if any, was ever given for the change to solid conductors with the change to metric sizes. Ditto for the change at the same time to bare copper in place of tinned copper.

As I've said, in the absence of any other reason, I suspect it may have been simply a question of cost. It presumably has to be cheaper to manufacture solid conductors than stranded ones. Similarly, if it was decided that tinning was 'not needed', then it would be cheaper to not tin than to tin. Having said that, the two changes surely weren't simultaneous? I'm pretty sure that nearly all of the Imperial PVC T&E I've seen has been bare copper.

One point of note on the comparison between British and American connections is that traditionally the 15 & 20A receptacles and switches used extensively with #14 & #12 cable in North America have screw terminals where the conductor is looped around under the head instead of the type employed on British sockets and light switches, making solid conductors ideally suited to the task (and also making it a case of "one conductor per terminal" by that method).

Interesting. There seems a lot to be said for 'one conductor per terminal', not the least because it allows the design of the terminal to be optimised, and makes termination more 'certain'. I have, in the past, seen double 13A sockets with dual L&N terminals, to facilitate 'one conductor per terminal', but that idea clearly hasn't caught on to any significant extent. Such a design obviously would need the internal connection between terminals to be able to carry 32A, but that didn't ought to be a problem for a solid bit of brass or copper. Are there reasons against this idea (other than cost) which I haven't thought of?

Kind Regards, John.

 

[ban-all-sheds]

What would be useful would be twin sockets with 1 terminal per conductor (each would have to have room for two though for spurs and for my wheeze)..

.. with ..

.. jumper bars between them (present by default so that you needn't use both sets of terminals if you didn't want to).

Need to extend the ring? Remove the jumpers, put the existing conductors into the separate terminals, add new cables to the new socket(s).

 

[securespark]

I tend to find with imperial stuff that when the cores are twisted together, they take up more space, ie if you don't twist them together they fit more easily into the terminal.

 

[securespark]

Surely then, that is not mechanically, and therefore not electrically, secure.

Not mechanically or electrically what, EFLI?

 

[sparkwright]

I find more and more terminals are now square instead of round, which don't seem to grip all the wires you masy terminate. Often you need to double the ends of the wires over.

When fitting two wires into a terminal and one is bigger than the other, I double the smaller one over.