Multiple conductors in terminals - installation method

[pls1]

When running multiple T&E cables into metal screw terminals such as in a junction box or back of a socket/switch. What tends to be the best method for doing this?
I seem to recall that twisting multiple conductors together is not good practice although I've seen it many times in reality. Sometimes I've seen the bare ends bent back over (doubled up) and inserted, although this doesn't tend to work well where there are more than a couple of cables in the terminal.
Just pushing the conductors in straight can also be problematic I've found occasionally especially with junction boxes where the screw terminals don't quite 'bite' all the cables together and there is a loose cable.

 

[EFLImpudence]

You seem to have found out yourself.

As you suggest it depends how many wires you want to put in the terminal.

One or two - I bend back the end on itself.
More than two - You may only be able to put them in straight.

But - NO TWISTING.

 

[seasickstevie]

Often if there are three cores entering (not the Irish singers - now that would be interesting ), I tend to bend back one core which effectively becomes two wires.

Then the other two I put in singularly alongside forming a square formation, if that makes sense.

That way there's usually no wasted space, and all are snug.

 

[Lectrician]

The tip was always "fill the terminals", bending over one or two to achieve this.

Two cables I put straight in, one I will double over. On larger accessories or terminals it becomes more common sence what to do.

NEVER twist. A real pain when it comes to fault finding, PIR's and remedial!

 

[JohnW2]

NEVER twist. A real pain when it comes to fault finding, PIR's and remedial!

True, for the reasons you give. Ironically/unfortunately, it is my belief that, if done carefully/properly, twisting (which seemingly was once the norm) probably results in the most reliable (i.e. safest) joints.

Kind Regards, John.

 

[ban-all-sheds]

I can't help thinking that if conductors were stranded things would be easier.

Can anybody who remembers working with Imperial cable confirm/deny?

 

[JohnW2]

I can't help thinking that if conductors were stranded things would be easier. Can anybody who remembers working with Imperial cable confirm/deny?

I don't really need a memory - there's still some Imperial cable in my installation here! I'm certainly inclined to your view that termination is probably easier. Twisting certainly is, but that's no longer regarded as a good idea for the reasons already stated (much more need to 'interfere' with termination than there was in the 'old days'!). It's undoubtedly quite easy to damage, or loose, a strand or two - but I frankly doubt that is a major issue.

I've often wondered why it was that the change from Imperial to metric was accompanied by a change from stranded to solid (albeit only for the smallest CSAs). There presumably was a perceived 'advantage', if only cheapness of manufacture - any idea?

Kind Regards, John.

 

[bernardgreen]

Stranded conductors make better joints than a single core of the same total cross sectional area as the total contact surface area of stranded conductor is greater than the surface area of the equivalent single core.

Even better when the strands of the two conductors are inter-meshed with each other in the terminal.

 

[stillp]

Stranded conductors make better joints than a single core of the same total cross sectional area as the total contact surface area of stranded conductor is greater than the surface area of the equivalent single core.

Not sure about that Bernard. The total surface area is greater, but the surface area that's available to make contact with the terminal is surely less than for a solid conductor.

 

[bernardgreen]

Contact with the terminal is not as critical as the wire to wire connection in the majority of cable to cable connections.

Even in the back of a 13 amp socket on a ring or radial the wire to wire current could be as high as 20 amps or more to sockets elsewhere while the wire to terminal current could be zero.

 

[stillp]

Contact with the terminal is not as critical as the wire to wire connection in the majority of cable to cable connections.

Even in the back of a 13 amp socket on a ring or radial the wire to wire current could be as high as 20 amps or more to sockets elsewhere while the wire to terminal current could be zero.

Ah OK, I see what you're getting at. I'm still not sure I agree though.

 

[JohnW2]

Not sure about that Bernard. The total surface area is greater, but the surface area that's available to make contact with the terminal is surely less than for a solid conductor.

It's certainly not a straightforward situation, but I would imagine that the much greater ability of the perimeter of a stranded cable to conform with the shape of whatever it's in contact with will often result in a greater contact area than would be the case with a solid conductor. To achieve the same contact area with a solid conductor would probably require that it be 'squashed' to an undesirable extent (which is probably what we generally do!)

Kind Regards, John.

 

[stillp]

Not sure about that Bernard. The total surface area is greater, but the surface area that's available to make contact with the terminal is surely less than for a solid conductor.

It's certainly not a straightforward situation, but I would imagine that the much greater ability of the perimeter of a stranded cable to conform with the shape of whatever it's in contact with will often result in a greater contact area than would be the case with a solid conductor. To achieve the same contact area with a solid conductor would probably require that it be 'squashed' to an undesirable extent (which is probably what we generally do!)

Kind Regards, John.

Hmmm. Depends on the relative dimensions of the terminal and the conductors, as well as the extent to which the solid conductor can be squashed.
i was thinking this needs RF and his welder, but I doubt that the difference in temperature rise would really be measurable.

 

[JohnW2]

Contact with the terminal is not as critical as the wire to wire connection in the majority of cable to cable connections. Even in the back of a 13 amp socket on a ring or radial the wire to wire current could be as high as 20 amps or more to sockets elsewhere while the wire to terminal current could be zero.

Indeed - and that's why, if there weren't now this need for people to be able to 'tamper' with the terminations (PIRs etc.), I think that twisting conductors probably would produce the most reliable (safe) cable-to-cable joint.

In fact, that's essentially how I was 'brought up'. Just as I was taught that solder should only be used to maintain a joint which had been made mechanically, I was also taught that a terminal screw should really only be maintaining a mechanical joint (e.g. produced by twisting or splicing).

Kind Regards, John.

 

[JohnW2]

Hmmm. Depends on the relative dimensions of the terminal and the conductors, as well as the extent to which the solid conductor can be squashed.

Yes, it's complicated, and subject to many variables. If one is prepared and able to squash a solid conductor enough, one can probably get something approaching perfect contact, but whether or not that is desirable is another matter. With a stranded conductor, one theoretically ought to usually be able to get good conformity with the shape of the terminal with less squashing - because some of the 'conforming' results from individual strands re-arranging their positions, rather than being squashed.
.

i was thinking this needs RF and his welder, but I doubt that the difference in temperature rise would really be measurable.

As you say, I doubt the difference would be measurable. In any event, I think the bigger issue is not the initial performance but the extent to which the joint remains good in the long-term. I suspect (essentially just intuition) that stranded cable terminations are more likely to remain satisfactory, but I might be wrong.

Kind Regards, John.