termination tightness

[calum63]

Hi, just a curious question that has been bugging me, just how tight do electrical connections need to be? whether its anything from lightswitch, socket terminals to choc blocks? Obviously if they are loose you run the risk of arcing and in worst case a house fire, or if they are too tight you end up snapping the conductor 1mm is very prone to this or maybe I'm just heavy handed.
Do connections just need to be tight enough so you can't pull the cable out the terminal and no more?
How do you know if a connection is tight enough or too loose? and at what point do you stop tightening to avoid snapping the screw or conductor?
thanks

 

[calum63]

....

You should look in the mirror my dear assuming it hasn't already cracked, New troll on this forum I see!. How pathetic your life must be

 

[mwatsonxx]

Well it's not like tightening your car wheel nuts.

The best I can think off (although I've done it 1000's of times) is, slowly tighten until you feel resistance then give another 1/8 turn. If you can pull the cable out it's obviously too loose. Its not an exact science.

 

[JohnD]

Copper is a soft metal and, under pressure, will flow a little. Sometimes you find an old terminal has gone loose. It seems to happen in large, stranded cables, e.g. in CUs where it has deformed over time. So it's often worth revisiting these and checking tightness a week or so after installation. However mighty you were when you fitted them, they may take a bit more of a turn.

Notionally a terminal should be "filled" meaning you may benefit from doubling over the end if it is a loose fit, especially if it is the sort where a single screw is driven down and (hopes to) catch the core centrally.

 

[ericmark]

You do get torque screwdrivers, however in industry there is an unwritten rule, one terminal one wire, what we do with a ring final putting up to three wires in one terminal would not have bin allowed. The panel would have links across terminals where more than one was required, and today with spring retention you simply could not put more than one wire in the hole however much you want to.
Necking off cables was a real problem as each service cable tightness was checked which is why the torque screwdrivers was used, also binding of screws either due to poor manufacture or a strand of flex so that's one reason for boot lace crisps, other is it holds cable number in place. There was a move to built in tags, so the screw does not turn against the cable, the tag only presses down, no turning, also helps stop the stray core binding the screw.
With so many different cables and terminals hard to give a rule, vibration and heat can cause screws to come loose and cores to compress, so the installation engineer has to decide on level of maintenance. This may be on a sliding scale, 1 month, then 1 year then every 5 years. Too often cables neck off, too far between cables can come loose.
Batching plants have a lot of vibration, a house has very little, so with a house often items never checked, with batching plant a regular maintenance job is to test all wires,so maintenance free terminals have been used for a long time. I first saw maintenance free in 1980 clearly around before then, today the wango is becoming more the norm.

 

[ban-all-sheds]

Well it's not like tightening your car wheel nuts.

But they too have recommended torque settings. I remember once using a torque wrench on mine, and I was surprised by how "un-tight" they were.

 

[rsgaz]

I was surprised by how "un-tight" they were.

It does feel like that, but when you see that a single M12 nut(10.9 grade steel), torqued to 122Nm, provides over 5 tons of clamping force, then you can see why you don't need to go crazy with the tightness of nuts and bolts.

 

[ban-all-sheds]

Indeed.

I think the point is that people who just use a wheelbrace and a Charles Atlas impression are probably way over-tightening the nuts.

 

[John D v2.0]

To be honest I don't tighten too much, but what I always do is get a long nose pliers and give each conductor a yank afterwards. This is more effective than resistance testing at finding an improperly made termination.

 

[JohnW2]

You do get torque screwdrivers ....

Indeed - but, as I have observed before, I have been quite shocked when I have tightened terminal screws on RCDs/MCBs etc. to the recommended torque, since the result seems to be a lot less 'tight' that I imagine most electricians would accept/tolerate if they were doing it 'manually'. They may, of course, all be 'over-tightening', but I personally do not feel comfortable with a terminal screw on which I can easily get a further 'half turn', or even 'quarter turn', manually, without much effort.

... however in industry there is an unwritten rule, one terminal one wire, what we do with a ring final putting up to three wires in one terminal would not have bin allowed.

It's not an unreasonable 'unwritten rule'. I'm a little surprised that we have not seen the evolution of ones like this (perhaps even with groups of three terminals, to accommodate spurs) (apologies for poor piccie!) ...

Kind Regards, John

 

[mattylad]

As an electrical assembler/wiresman I have a similar rule (knowing that you cannot always have just 1 wire per terminal) that I never fill the terminal with more than 80% of its size of wire.
I see colleagues (and Electricans at that) who stuff 3 wires (2x1.5mm and 1x0.75mm) into a 3.2mm diameter terminal block, twisting it and generally making a mess of the connections, pulling them out shows that at least 1 wire is not fully inserted.

I modified how the connections were made so that at most only 2 wires are inserted and not fully filling the terminal, I can always use larger or more terminals if needs be.

How tight? As tight as hand tight and a little thrutching, giving a good thrutching is only reserved for the big terminals.
I use a torque set tool as I can no longer screw all day like the young ones do (lol) as it gives my hand cramps and my middle finger tends to fold back.
What torque setting do I use? on terminals its no4, on M4-5 screws\bolts its no10 - what nmdo these relate to? buggered if I know, we dont have a rotational toque measurement device - but they feel about right

 

[ban-all-sheds]

I'm a little surprised that we have not seen the evolution of ones like this (perhaps even with groups of three terminals, to accommodate spurs)

And with push-in MF terminals.