RCBO terminals

[maltaron]

Just had a problem trying to connect a ring final to a MK RCBO. No matter how tight the screw it would not grip 2 X 2.5mm cables. Has anyone else had this problem and if so, how did you rectify it?

 

[Iggifer]

if you take the rcbo out of the board does the terminal close fully?

 

[maltaron]

The terminal closes fine with no cable and clamps single 2.5 OK. With 2 X 2.5 one cable is tight and the other pulls out.

 

[sparkwright]

Just had a problem trying to connect a ring final to a MK RCBO. No matter how tight the screw it would not grip 2 X 2.5mm cables. Has anyone else had this problem and if so, how did you rectify it?

Very common problem.

I strip a bit more off the end of each wire, and fold the end over.

 

[Scoby_Beasley]

Also stand your cables like soldiers. i.e. in a line, next to each other. If they're crossed over in the cable clamp you are virtually doomed to failure.

 

[JohnW2]

Also stand your cables like soldiers. i.e. in a line, next to each other.

... is that not the very arrangement in which, if they are fractionally different in size, it becomes difficult to grip all of them adequately? Allowing as much separation as one can get between the conductors may help - since the movable part of the cage can then 'tilt' slightly in order to adequately grip conductors of fractionally different sizes.

Kind Regards, John

 

[securespark]

But these are the same size. Am I missing something?

 

[JohnW2]

But these are the same size. Am I missing something?

They are nominally the same size, but the real world being the real world, there is likely to be a fractional difference - particularly after the cables have been handled, stripped, bent etc. (and certainly after the initial attempt to clamp them in a terminal).

If the moveable part of the cage couldn't tilt at all, it would have to compress the (fractionally) fatter conductor to exactly the same size as the (fractionally) thinner one before it could grip both simultaneously and equally. As I said, there presumably always is a little 'tilt' avaialble', and the benefit of that will, I would have thought, theoretically be at its greatest when the two conductoirs are as far apart as possible.

Kind Regards, John

 

[sparkwright]

But these are the same size. Am I missing something?

They are nominally the same size, but the real world being the real world, there is likely to be a fractional difference - particularly after the cables have been handled, stripped, bent etc. (and certainly after the initial attempt to clamp them in a terminal).

If the moveable part of the cage couldn't tilt at all, it would have to compress the (fractionally) fatter conductor to exactly the same size as the (fractionally) thinner one before it could grip both simultaneously and equally. As I said, there presumably always is a little 'tilt' avaialble', and the benefit of that will, I would have thought, theoretically be at its greatest when the two conductoirs are as far apart as possible.

Kind Regards, John

If all that stuff is right, why don't they make round tunnel terminals like older consumer units had?

It seems to me that 'square' terminals are just not up to the job, as I have noted on some socket brands nowadays.

 

[JohnW2]

If all that stuff is right, why don't they make round tunnel terminals like older consumer units had?

If you are referring to 'traditional' terminals, in which one tightens a screw directly onto the conductor(s), then I think that's probably even worse (than 'cage' or 'bar' terminals), particularly when one is trying to terminate two or more conductors in the same terminal.

I suspect the truth probably is that there is no fully satisfactory way to terminate two or more conductors into a single terminal (of any sort) - so the ideal might well be to provide two or more separate terminals. In the 'good/bad old days', electricians would have twisted the conductors together - but there are good reasons for not doing that!

Kind Regards, John

 

[EFLImpudence]

I think the only problem with RCBOs is the depth of the terminals and therefore the difficulty of positioning one wire on each side of the clamp without being able to see where they are.
In fact they seem deeper than they appear.

Even if the conductors do seem tight they may only be held where one conductor has crossed the other.

 

[JohnW2]

I think the only problem with RCBOs is the depth of the terminals and therefore the difficulty of positioning one wire on each side of the clamp without being able to see where they are. In fact they seem deeper than they appear. Even if the conductors do seem tight they may only be held where one conductor has crossed the other.

Yes, that makes sense. However, the problem the OP described is not (at least, IME) unique to RCBOs - I've experienced it (with multiple conductors) with other things that use bar/cage clamps (including MCBs), even when one has a good view of what one is doing. Have you not?

Kind Regards, John

 

[EFLImpudence]

I've experienced it (with multiple conductors) with other things that use bar/cage clamps (including MCBs), even when one has a good view of what one is doing. Have you not?

Not really.

It's rare to have more than two conductors in one clamp, isn't it?

To be honest, I cant think of a way to describe how it would be satisfactory in every case.
If the clamp twists or bends to accommodate the wires then obviously one could remain 'looser'.
Having said that, are the clamps not ridged horizontally to bite into the copper slightly and prevent them deforming (too much)?

 

[JohnW2]

Not really. It's rare to have more than two conductors in one clamp, isn't it?

Sure - but two is obviously common. When I wrote 'multiple', I meant 'more than one' (and most commonly two). More than two (which I agree is rare, but not unknown) presumably magnifies the potential problem being discussed.

If the clamp twists or bends to accommodate the wires then obviously one could remain 'looser'.

Swings and roundabouts there, I reckon. As I said before, a little tilting (or twisting or bending) of the clamp might actually facilitate better tightening onto both of two conductors.

Kind Regards, John