SWA bend radius

[bernardgreen]

The bending radius for the internal cores and the internal sheath is significantly smaller than the radius for the entire cable

Hence one option might be to terminate the armouring in a water proof metal box on the external wall and then route the cores and internal sheath and of the back of the nbox and through the wall via a suitable protective conduit along with an earth conductor from the armour termination gland.

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• bernardgreen
• 10 May 2009
• 17

 

[ban-all-sheds]

I understand how that works 'on' a wall, but is it going to be possible to do the same when 'going through' a wall without have to remove two or more bricks?

First, a disclaimer - I didn't try to visualise the route the OP's cable has to take.

 

[JohnW2]

The bending radius for the internal cores and the internal sheath is significantly smaller than the radius for the entire cable

I have been wondering about that. It might be a heretical suggestion, but I wonder whether the specified 'minimum bending radius' of the entire cable really 'matters'?

Hence one option might be to terminate the armouring in a water proof metal box on the external wall and then route the cores and internal sheath and of the back of the nbox and through the wall via a suitable protective conduit along with an earth conductor from the armour termination gland.

Indeed. In fact, if the OP had some reason for wanting SWA to continue all the way to the CU (e.g. if some of the internal cable were buried, but without RCD protection), it would be possible to 'break' the SWA within such a box and have the ongoing cable also in SWA (would probably involve a gland on the back of the box, requiring some excavation of masonry to accommodate it).

Kind regards, John

 

[JohnW2]

First, a disclaimer - I didn't try to visualise the route the OP's cable has to take.

Nor did I, in detail. However, is not the main issue described that the cable needs to come through a wall, roughly perpendicular to the surface of the wall, and then make a 'sharp', roughly 90° turn, in order to run down the surface of the wall (i.e. conceptually along the lines of flameport's diagram)?

Kind Regards, John

 

[EFLImpudence]

I will be running some 16mm^2 3-core SWA. ... However, the final end of the run goes 2.5m up an exterior wall, w/ a sharp 90 degree bend through masonry and some 1st floor joists to the CU.
.. I don't have much room to get a decent radius on it since the run will be through the joists and so there is a good chance the cable will kink.

It would appear the cable is coming IN through the wall, although I suppose it could be run either way.

So, coming in through the wall doesnt seem to be a problem with methods already described.
Once inside it is proposed to run through joists with what may be a sharp bend, depending how far the entry point is from the joist.

Therefore, wouldn't it be better to notch the top of the joists wherever the cable runs.

 

[dobby1]

Thanks for the input guys.

Just an update, the walls are not double skinned, it is single skin 200mm blockwork. Picture attached for further clarity.

 

[phatboy]

The floor cavity is really 100mm? That must be a floor that's very bouncy, and not suitable for a piano?

 

[ban-all-sheds]

I will be running some 16mm^2 3-core SWA.

Is it supplying the CU, or a final circuit from it?

 

[dobby1]

The floor cavity is really 100mm? That must be a floor that's very bouncy, and not suitable for a piano?

Don't think I'd put a piano on it, but it feels robust, apart from some creaky floorboards. The entire house is somewhat peculiar, but let's not get into that.

Is it supplying the CU, or a final circuit from it?

CU

 

[JohnW2]

Don't think I'd put a piano on it, but it feels robust, apart from some creaky floorboards.

Are you planning on drilling fairly large holes in those 100mm joists? If so, that sounds a little iffy to me.

CU

As a matter of interest, where is it coming from, then?

Kind Regards, John

 

[dobby1]

Are you planning on drilling fairly large holes in those 100mm joists? If so, that sounds a little iffy to me.
As a matter of interest, where is it coming from, then?

Fortunately, the run is perpendicular to the the joists, so no joist drilling is required. The SWA O/D is 25mm so that would be 1/4 the joist length which is pretty significant so thankfully I don't have to worry about that!

It is a connection between the mains CU and an outbuilding.

 

[ban-all-sheds]

How far away?

Which country of the Union do you live in?

 

[Simon35]

The floor cavity is really 100mm? That must be a floor that's very bouncy, and not suitable for a piano?

Depends on the span of the joists, 4" by 2" can span 6 ft, I believe from memory, from holidays spent working with my Dad (a builder)

 

[JohnW2]

Depends on the span of the joists, 4" by 2" can span 6 ft, I believe from memory, from holidays spent working with my Dad (a builder)

Yes, I think it's something like that, but I imagine that it's fairly unusual to have load-bearing walls that close to one another.

I haven't had to think about such things for a long time. Whether one calls it 'unnecessary over-engineering' (due to ignorance) or what, my present house was built in the days when they "built houses like wot they don't do anymore", since many of my floor joists are 10" x 3", and some even 12" x 4"! Mind you, it's a pretty big house, but none of the spans actually 'require' joists anything like that big.

Kind Regards, John

 

[ban-all-sheds]

Makes loft conversions a POP though....