"tapping off" a garden feed

[bernardgreen]

Cast resin joints for SWA cables are far more expensive than cast resin joints for "ordinary" non SWA cables.

And also much more difficult to make the joint in SWA

 

[Harry Bloomfield]

And also much more difficult to make the joint in SWA

SWA joints, depending on what you call ordinary, are really not that difficult to do. I must have done quite a few in my working life.

 

[flameport]

And also much more difficult to make the joint in SWA

They are not.

Strip the ends of the cables
Connect conductors together
Apply constant force spring around the armour with the braid under the spring
Clip plastic case around the joint
Seal with tape
Pour in resin.

Example for small cables: https://www.cef.co.uk/catalogue/pro...h-resin-joint-kit-for-cables-up-to-4mm-4-core

 

[bernardgreen]

I was assuming that the intention was to "tap off" from an existing cable which would involve cutting the SWA in situ to get access to the conductors.

 

[crystal ball]

They are not.

Strip the ends of the cables
Connect conductors together
Apply constant force spring around the armour with the braid under the spring
Clip plastic case around the joint
Seal with tape
Pour in resin.

Example for small cables: https://www.cef.co.uk/catalogue/pro...h-resin-joint-kit-for-cables-up-to-4mm-4-core

All very well, carrying that out in a wet trench without any slack on the cable increases the difficulty

 

[bernardgreen]

carrying that out in a wet trench without any slack on the cable increases the difficulty

So much easier with waveform cable ( as used by DNO ) where the armour is not wound around the conductors and connections to Live and Neutral are "spiked" into the connectors.

 

[Stringman_uk]

I have put joints in SWA cable, but the joints are not cheap, so normally one would run the new cable from either the house or the existing out building, one would not join two cables.

Today we want RCD protection, either using a stand alone RCD or a RCBO which is a RCD and MCB combined, using the RCD method it is common to have many MCB's from one RCD, if this is already the case in your house, then adding further RCD's or RCBO's is a bit pointless, OK with a 10 mA RCD fed from a 30 mA RCD in theory the 10 mA should trip first, but often simply pressing the test button will trip both, so start point is what have you already got in the house?

View attachment 307208RCD's as seen here have test buttons.

The next point is building construction, with a brick building a TN-C-S supply is normal, with the supplier (DNO) providing the earth, however with a metal building this may not be safe, so a metal shed will likely need a TT supply, {url=https://electrical.theiet.org/media...s-a-supply-to-a-detached-outbuilding.pdf]this tells one how to wire an out building[/url] although a little out of date and this explains the problems with supply type but it does not end there, clearly we have services already under many gardens, be it water, gas, drains or electric, so knocking in earth rods not only can they hit existing services, but where the existing are metal, they can also cause problems with the earthing.

So when an electrician visits he looks at the area and works out the best option to use, I would not expect a problem with my garden, but that does not mean no problem with yours.

I have at work been approached by some one asking how to do XYZ, and have given advice, then at a latter date visited their home, and realised my advice was not really appropriate for their home, so would suggest you get an electrician to quote for the work, and ask what will need to be done, one it may be cheaper than you think to get it done for you, and two you will get a better idea to if there is anything in your home which may impact on the work required.

erikmark thanks for the detailed reply
In the house I have the 32a mcb with a RCD covering all the breakers the I cant see the size stamped on the outside of the cable leading up to the summerhouse but it does have bs6726 stamped it is about 15mm wide, The additional cable I have is a 2,5mm armoured cable.
The consumer unit in the summerhouse is in the photo below.
Obviously there isnt room for a spare breaker.
So i was thinking of swapping it out for a a untit with space for 3 breakers with the 3rd being for the office?
Would this have to be 16A or could it be 32A?

 

[Harry Bloomfield]

In the house I have the 32a mcb with a RCD covering all the breakers the I cant see the size stamped on the outside of the cable leading up to the summerhouse but it does have bs6726 stamped it is about 15mm wide,

6mm T&E is 13.7mm wide.

 

[Stringman_uk]

6mm T&E is 13.7mm wide.

Thanks harry is that armoured T&E as the other piece I have measures about 13mm (maybe less) but says 2.5mm.
If the original cable is 6mm then I presume there would be no problem with changing the cu above to one with 3 breakers and having a 32a breaker to feed the office?

 

[Harry Bloomfield]

Thanks harry is that armoured T&E as the other piece I have measures about 13mm (maybe less) but says 2.5mm.
If the original cable is 6mm then I presume there would be no problem with changing the cu above to one with 3 breakers and having a 32a breaker to feed the office?

If it's 2.5mm, then it needs to be a 20a MCB.

 

[Taylortwocities]

https://www.diynot.com/diy/attachments/20230703_143559-jpg.307300/

I see you have an RCD as the main switch in the outbuilding. That is pointless as the feed circuit is already RCD-protected.
Actually bad design as a fault in the garden circuit will trip all of the power in the house.

 

[SUNRAY]

Thanks harry is that armoured T&E as the other piece I have measures about 13mm (maybe less) but says 2.5mm.
If the original cable is 6mm then I presume there would be no problem with changing the cu above to one with 3 breakers and having a 32a breaker to feed the office?

IF You opt for connecting from your existing outstation and use 6mm² cable, there is no requirement to 'fuse down' and the new addition may simply be teed from the 'live side' of the outstation consumer unit:

 

[Stringman_uk]

https://www.diynot.com/diy/attachments/20230703_143559-jpg.307300/

I see you have an RCD as the main switch in the outbuilding. That is pointless as the feed circuit is already RCD-protected.
Actually bad design as a fault in the garden circuit will trip all of the power in the house.

YEP
it has done that a few times!!!
it was inherited when we bought the house.
what would you suggest as an alternative?

 

[Stringman_uk]

IF You opt for connecting from your existing outstation and use 6mm² cable, there is no requirement to 'fuse down' and the new addition may simply be teed from the 'live side' of the outstation consumer unit:
View attachment 307387

Sunray
Thanks for that, but I presume the over riding factor for that is to have 6mm cable- if i stuck with the 2.5 could i run it from a breaker?
I suppose its a case of buy new cable or buy a new cu for the summerhouse ( though, to be fair, I would use the old one in the office)

 

[Taylortwocities]

Sunray
Thanks for that, but I presume the over riding factor for that is to have 6mm cable- if i stuck with the 2.5 could i run it from a breaker?

That would constitute a new circuit. Then you are into LABC involvement, notification and other issues. The only sensible route is to use a registered electrician.