Termination of SWA on distant end of TT supply

[JohnW2]

Yes, I'm not sure either about the copper equivalent for 10mm SWA but (and I have not looked up the regs so may be wrong) is the 10mm (minimum CSA) not mandatory as a discrete protective conductor (just like within the main dwelling) since the workshop now becomes an extension of the main dwelling from the perspective of exporting PME?

As far as I am aware there is no explicit requirement for bonding conductors to be 'discrete', even in the main dwelling (although there would be no reason not to be in the main dwelling). Using SWA for the purpose we are discussing is, I think, a well-used practice.

Kind Regards, John.

 

[JohnW2]

Yes the 10mm2 is the minimum size, I seem to recall we discussed this recently and 6mm2 with a core and the SWA in parallel is greater than 10mm2 copper equivalent, so 10mm2 will be more than adequate

Indeed. It was actually me who calculated and posted those figures, but I've forgotten in which thread!

Kind Regards, John.

 

[sparkticus]

As far as I am aware there is no explicit requirement for bonding conductors to be 'discrete', even in the main dwelling (although there would be no reason not to be in the main dwelling). Using SWA for the purpose we are discussing is, I think, a well-used practice.

You are probably right. In most cases I add an additional 10mm CSA protective bond back to the main dwelling MET but that is out of habit (and good practice in my mind)
I guess I just do not trust SWA glands, they don't seem to let you 'grip' very much of the armour in the gland (even if one internal core is also designated as a CPC)
I used to trust MIC but its getting difficult to get hold of it and expensive - not that all MIC outer shields have a copper equivalent to 10mm CSA.

 

[JohnW2]

You are probably right. In most cases I add an additional 10mm CSA protective bond back to the main dwelling MET but that is out of habit (and good practice in my mind)

..but how do you do that? In outdoor situations such as we're talking about, the SWA is usually buried, and you can't just bury an unprotected 10mm² G/Y cable alongside it.

I guess I just do not trust SWA glands, they don't seem to let you 'grip' very much of the armour in the gland (even if one internal core is also designated as a CPC)

If properly done, I think the gland will grip all of the armour, but I'm always a little uneasy about how tight the connection necessarily remains, so I've never relied on armour alone for CPC function. I have seen people strip back some of the outer sheath and attach a clamp - but I don't think that comes into the category of 'good practice'!

Kind Regards, John.

 

[sparkticus]

..but how do you do that? In outdoor situations such as we're talking about, the SWA is usually buried, and you can't just bury an unprotected 10mm² G/Y cable alongside it.

I get involved in a lot of temporary supplies/sub-mains. Most are surface mounted so I clip the additional 10mm/16mm G/Y along with the SWA.
If buried then I often cable-tie the G/Y to the swa and bury direct. If longer term then I still cable-tie but run the whole thing in ducting.

 

[sparkticus]

On occasions I have taken a different rout (surface) with the G/Y than that of the SWA.

 

[JohnW2]

If buried then I often cable-tie the G/Y to the swa and bury direct. If longer term then I still cable-tie but run the whole thing in ducting.

Admittedly it's 'only' a bonding conductor (or CPC, depending on how you look at it), but I'm not sure that burying of an unprotected non-armoured cabled has ever been compliant with the Wiring Regs - and as for 'burying in ducting' (theoertically compliant with BS7671:2008, given satisfaction of some conditions), there have been some fairly robust discussions here as to what constitutes acceptable ducting! If I really had to run a dedicated buried protective conductor, I think I'd use SWA (cores+armour)

Kind Regards, John

 

[sparkticus]

but I'm not sure that burying of an unprotected non-armoured cabled has ever been compliant with the Wiring Regs -

I don't disagree but keep in mind I do it for a lifetime of about two weeks (not that two weeks is a short enough period for someone not to stick a shovel through the G/Y but unlikely) and I don't bury very often. Mostly clip surface.

To play the advocate of the devil card, what is your opinion of the many unprotected (partially buried) G/Ys that connect earth rods to METs in TTs?

 

[RF Lighting]

Have a read of table 54.1

 

[sparkticus]

Have a read of table 54.1

I don't have it with me but its something like:

-protected against mechanical damage 2.5mm CSA (assuming copper)
-Not protected 16mm CSA (assuming copper

-Not protected from corrosion 25mm (assuming copper)


For temporary supplies I often use 16mm but I tend to ignore the corrosion because it often comes up after less than two weeks (temporary equipment)

 

[JohnW2]

To play the advocate of the devil card, what is your opinion of the many unprotected (partially buried) G/Ys that connect earth rods to METs in TTs?

As others have pointed out, there are regs to be considered - but if it were totally up to me, I'd be fairly happy provided protection from accidental mechanical damage was reasonable.

Kind Regards, John.

 

[1550]

And if the 10mm is tied below the swa it's going to be just about bullet proof anyway, unless a digger gets it- then the lots gone anyway

 

[viewer]

This is a sort of link between the post 'what earth is this?' and this post. House was on TT. Had a 180 ohms, but dry ground. Recently DNO put in a new pole and PME.
House now 0.88 ohms. Garage connected with SWA via switched fuse and RCD in house. CPC connected at house and isolated in garage. Armour connected in house and isolated in garage. Plastic box. CPC from new circuit to rod, so garage now TT; couldn't export earth as system continues to second garage. RCD also in garage (I know, but it was acting as isolation switch so left it) New test shows 1.3 ohms on new TT circuit. The ground is wet. Suspect that the PME connections from the local poles are having a good influence. Is this possible? - and anything wrong with the layout as described?
Thanks

 

[sparkticus]

And if the 10mm is tied below the swa it's going to be just about bullet proof anyway, unless a digger gets it- then the lots gone anyway

That actually happened to me last week. The digger went through a new 16mm sub-main (SWA) as I was doing dead testing. Thought my multifunctional was broken for moment until someone tapped me on the shoulder and said "is that your cable out there wrapped around the digger bucket"

 

[sparkticus]

Suspect that the PME connections from the local poles are having a good influence. Is this possible? - and anything wrong with the layout as described?
Thanks

Layout seems OK to me regarding first garage. Does second garage have its own rod?

1.3 ohms is way too low for any mass of earth path. suspect you have a "wired" parallel earth path.