SWA too big for its Box

[monday]

I am terminating 2.5mm2 SWA into a Metalclad spur unit from where it continues in twin and earth. The spur unit has only one earth terminal which is pretty much filled by the SWA earth core, being multi-strand rather than solid core, so room for the other earth or the earth link to the box. Can I:
(i) connect the incoming and outgoing earths together directly via terminal strip, with links from there to the earthing point on the spur unit and the back box? or

(ii) terminate the SWA into its own box, then connect this to the spur unit in twin and earth? or

(iii) find a metalclad spur unit with more or bigger earth terminals (MK??)?

Thanks for help.

 

[JohnW2]

I am terminating 2.5mm2 SWA into a Metalclad spur unit from where it continues in twin and earth. The spur unit has only one earth terminal which is pretty much filled by the SWA earth core, being multi-strand rather than solid core, so room for the other earth or the earth link to the box.

I'm a little surprised that the terminal can't take more than that, but ....

Can I: (i) connect the incoming and outgoing earths together directly via terminal strip, with links from there to the earthing point on the spur unit and the back box? or

You could, but I wouldn't have expected that t be necessary. Isn't the terminal in the box big enough for the two conductors, from which just one conductor (which would probably only need to be 1.5mm²) from there to the accessory?

(ii) terminate the SWA into its own box, then connect this to the spur unit in twin and earth? or

Yes, you could do that.

(iii) find a metalclad spur unit with more or bigger earth terminals (MK??)?

Others may be able to help you with that one! What make do you currently have?

Kind Regards, John

 

[monday]

Thanks John W2. Its a Telco spur unit. The terminal will take the SWA earth core + 1.5mm2 earth core of the T&E but no room for another 1.5mm2 earth link to the terminal on the box. And the multi-strand SWA core doesn't seem to anchor very well with the solid core earths.

I'm sure some spur units have two linked earth terminals so that the SWA could go in one and the two solid cores in the other - seems more secure somehow?

 

[PrenticeBoyofDerry]

it unusual for a fused connection plate (I assume this is what we are talking about), only to have the one earth terminal, but I am also surprised that two the CPC of the SWA at 2.5mm, the CPC of the twin and earth and the box link both likely to be 1.5 mm, will not squeeze into the one terminal.
I suggest if that is the case take it back and swap for one that can terminate the CPCs and link.

 

[JohnW2]

Thanks John W2. Its a Telco spur unit. The terminal will take the SWA earth core + 1.5mm2 earth core of the T&E but no room for another 1.5mm2 earth link to the terminal on the box. ...

You could presumably connect the SWA earth and a 1.5mm² link to the spur unit to the earth terminal in the box, and then connect the earth of the T&E (together with the link conductor) to spur unit - but ...

...And the multi-strand SWA core doesn't seem to anchor very well with the solid core earths.

Indeed - and that's the reason why it is not recommended to try to put solid and stranded conductors into the same screw terminal, so ...

I'm sure some spur units have two linked earth terminals so that the SWA could go in one and the two solid cores in the other - seems more secure somehow?

Most do - presumably at least partially because (as above) it's very common for one solid and one stranded conductor to be involved. You'd therefore be best advised to find one that does.

Kind Regards, John

 

[PrenticeBoyofDerry]

You could try bootlacing the stranded cable.

 

[JohnW2]

You could try bootlacing the stranded cable.

That would solve the problem of having solid and stranded in the same terminal, but a ferruled conductor is presumably bigger than an unferruled one, so the 'no fitting' problem probably would get worse. However, it might work with my suggestion of taking SWA and T&E CPCs to the box terminal, then a link from there to the FCU.

I'm still pretty amazed that there is such a thing as an FCU (assuming that's what we're talking about) with only one 'earth' terminal, for the reason I mentioned.

Kind Regards, John

 

[333rocky333]

Wago push on connecters are good for these cases, push all the earths in plus 1 or 2 singles out to the accesory and box, personally id get an mk spur they have two earth terminals plus one in the back box or do as above and have two wires in each terminal

 

[333rocky333]

Another option if you have a crimper is too lug all the cores and fit on a brass nut and bolt with the banjo fitted

 

[JohnW2]

Wago push on connecters are good for these cases, push all the earths in plus 1 or 2 singles out to the accesory and box ...

Given that one of the conductors is stranded, wouldn't one need to use a Wago 'lever' connector, rather than a push-on one?

... personally id get an mk spur they have two earth terminals plus one in the back box or do as above and have two wires in each terminal

Same here, but I suspect that most makes (not just MK) actually have two earth terminals. As I've said, one of the common uses of an FCU involves flex on the output side, so it really is desirable not to have to put a stranded and solid earth conductor into the same terminal - hence, I imagine, the usual two earth terminals.

Kind Regards, John

 

[monday]

Many thanks to all for the suggestions. I hadn't thought of using the box terminal but given the multi-strand/solid core issue (and John W2's confirmation that it is not recommended) I think I will look for an MK or similar metalclad spur unit with two earth terminals.

But be warned - the Telco fused switched spur unit only got one!

 

[JohnW2]

Many thanks to all for the suggestions. I hadn't thought of using the box terminal but given the multi-strand/solid core issue (and John W2's confirmation that it is not recommended) I think I will look for an MK or similar metalclad spur unit with two earth terminals.

I think we're all agreed that would probably be the best solution. However, as I've just said, a Wago lever connector would be another solution, since the solid and stranded conductors would each have their own 'holes'!

But be warned - the Telco fused switched spur unit only got one!

Thanks - that's good to know. As I've been saying, I suspect it is one of (maybe the only one of!) the few makes which is like that

Kind Regards, John

 

[333rocky333]

Wago push on connecters are good for these cases, push all the earths in plus 1 or 2 singles out to the accesory and box ...

Given that one of the conductors is stranded, wouldn't one need to use a Wago 'lever' connector, rather than a push-on one?

The push on ones are ok for 1.5 or 2.5 stranded less than 7 cores, but not flex.
The lever ones are ok for flex

 

[JohnW2]

The push on ones are ok for 1.5 or 2.5 stranded less than 7 cores, but not flex. The lever ones are ok for flex

Does the core of 2.5mm² SWA come into the former category - I'm not sure without looking (although I would have expected it to have 7 strands or more)?

Whatever, given that both types are available, and similar in price, I don't think I would be the person who tried to push any sort of stranded conductor into a 'push-in' one - but maybe I'm just a coward

Kind Regards, John