Let's twist again

[stunlawless]

Morning everyone,

When there are more than one cable to go into an accessory terminal (RF circuits), should the cable ends be twisted together or not ?

Similarly, when there is only one cable to go into a termonal ina socket outlet, should the cable end be doubled over ?

I've got both methods in my place, just wondered whatthe pro's opinion on best practice is.

Thanks, David

 

[ricicle]

Do not twist solid conductors together - they can snap off under the screw.
If you can get two doubled over conductors into the terminal all the better.
As my old college lecturer said on many occasions -"you must fill the terminal"

 

[Chri5]

No need for twists.

The terminals accepted groups of cores straight and clamp better and firmer on to straight rather than twisted.

As for bend back singles, again no need.

Just double check your terminations and give them a bit of elbow to make sure the terminals have tight contact on all cores.

 

[holmslaw]

..

 

[stunlawless]

Morning everyone,

I just did a search (don't shoot me for doing things in the wrong orderjavascript:emoticon('')), and everytime this question comes up, the answer is the same, so the answer is clear - don't twist !

Would it be a good thing to remake twisted connections whenever I find them, or is it better to let sleeping dogs lie ?

Thanks, David

 

[wingcoax]

It depends if you have enough spare cable to remake connections, I find that there is'nt always enough.

 

[comms]

Me personaly I dont twist conductor pairs but I do double over single conductors.

 

[bernardgreen]

I personally wrap the earth wires together to provide some chance of keeping continuity should the screw in the earth terminal lossen itself.

Not twisted ( where the wire is twisted ) but holding the wires loosely with the fingers while wrapping them round each other.

It was something a few old style electricians used to do. ( back in the old days pre 1960....)

For live and neutral I do not wrap. But I do ensure there are enough strands in the terminal for the screw to bite onto without the strand going sideways and out form under the screw.

 

[ericmark]

As an industrial electrician I was always taught one wire one hole and two wires need two holes. When building a board I would ensure there were enough terminals for the wires. With the maintenance free terminals this is a must there is no way two wires can be put in one hole unless you use a ferrule. You can get boot lace ferrules designed to take two cables but of course once crimped there is no way to separate for testing.

The domestic market is done on the cheap and often there is no alternative to using two wires in one hole and to lightly twist the wires together does reduce the chance of one wire not being gripped and removes the need for boot lace ferrules but of course it also means should it need removing for testing the cables will be weakened each time they are tested.

However also tighting screws on terminals can also cause necking and failure which is why there has been a move to maintenance free terminals especially with German equipment.

So the Electrician needs to balance the likely hood of a cable not held firm and need for maintenance. Since all cables in 13A sockets are the same size 2.5mm and no more than three I see no need to twist cables used with the live wires on sockets. However often there are more earth wires and some times it is safer to give a little twist but I can't see how you can really create any rule as to twist or not to twist. Best would be one terminal one wire then the question does not arise.

I do note however that MK do say you can fit three wires in the holes of their sockets. So there is nothing wrong with using three wires but once you try four or more then I think the chances of one wire not being gripped is too high to not twist them. Hopefully you should never need more than 3 so the situation should not arise.

 

[sparkybird]

What really annoys me though is when the cpc's have been completely twisted togther in the board (usually an old choc-a-block wylex one) and sleeved with one piece of sleeving. It makes it a nightmare to do PIR's properly

 

[VanSolo]

What really annoys me though is when the cpc's have been completely twisted togther in the board (usually an old choc-a-block wylex one) and sleeved with one piece of sleeving. It makes it a nightmare to do PIR's properly

That really is one of my pet hates. Did a db change recently where every RF circuit had been done like this, and up to three lighting cicuits at a time in a bunch with cpcs twisted in one earth sleeve.

 

[sparkybird]

Although I picked up a useful tip (maybe from here?) to do ring continuity tests and r1+ r2 at a socket if access at the board is a nightmare - saved my bacon a few times!

 

[Taylortwocities]

Good tip!

 

[stunlawless]

Hallo Everyone,

What I've picked up here is that wires should NOT be twisted together in most circumstances.

However, a few people have made some good points:

1. Ideally, one wire, one hole.

2. Most domestic accessories don't provide this, so, at some point, it will be necesary to fit two or more wires in one terminal.

3. Care must be taken to make sure all wires are gripped by the screw. Gentle twisting might be beneficial when three or more (protective conductors usually) wires need to go into the same terminal

4. A screw is not the best way of gripping wires - it can promote necking and fracture

5. Springy mechanisms ("maintainance free") are better (providing there is a means of removing the wire for testing without damage to the wire or terminal. These are, by definition, one hole one wire designs. Better still is a clamp design (like on all the mcb's etc I've ever seen).

6. Opinion is divided on "doubling back" on single wires. Seems that it might be better to do this to ensure the wire is gripped by the screw where it's a small wire in a large terminal, or the screw is small compared to the terminal hole (to avoid pushing the wire to one side of the screw).

Thanks for all the replies - some really good info.

David

 

[SparkyNinja]

I remember my old lecturer (and this is quite a few years ago now) saying to me that twisting solid conductors together would understandably require the use of a tool, pliers or whatever.
Now when you grip the end of the conductors and twist them, you cause strain on the cables and the twisting action can affect the csa of the conductor being installed. This could cause the cable diameter to be weakened/thinned creating a smaller conductor, causing heat then fire yada yada yada..

Now, maybe he was being a bit anal. But this has always seemed a good excuse as to why that particular practice shouldn't take place and so it has kinda stuck with me.

Anyway, didn't see this mentioned so thought I would throw it in there.