Power to outbuildings

[dornfield]

I would like to run power out to a 'summer house' and greenhouse. Two separate buildings. A huge part of the expense is likely to be digging a trench from the house out to the two buildings. The furthest run is likely to be about 100m from the house (electrical source) to the greenhouse. I'd like to do that labour intensive part myself, but leaving the connections at either end to a qualified electrician. There would also need to be a junction at about 60m out, splitting power to the summer house and greenhouse: that junction box would also need to be buried.
Is this achievable? How deep does armoured cable need to be (beneath a lawn, but also spanning the underside of a little bridge across a tiny stream)? Can the same power cable be used to power 3 pin sockets and lighting, which is likely to be low voltage LED in the greenhouse at least.

 

[Murdochcat]

Do not bury any form of junction box is my advice.

go to building 1 then on to building 2

as for armoured cable there is no advice on depth, but burying ducting with a draw cord is a good move

 

[bernardgreen]

It may be better to run two cables from the house rather than a junction box. Has the added advantage of the summer house and the green house each having their own MCB/RCBO in the house.

Consider the use of a TT supply to the buildings rather tha exporting the Earth from the consumer unit. This would require an Earth electrode ( Ground rod ) at each location. Laying an earth mat at the bottom of the trench would provide a very effective Earth electrode.

Discuss the Earthing methods with the electrician before you start digging trenches,

 

[bernardgreen]

Lights can be run off a power circuit by using switched FCU as the switch with a 3 or 5 amp fuse.

Not a good idea to use an FCU as an ON-OFF switch for a lamp ( or any other frequently used item ).

A switch will be rated for several thousand ( if not tens of thousands ) of operations, An FCU may have a much lower rating.

 

[Taylortwocities]

Not a good idea to use an FCU as an ON-OFF switch for a lamp

Eh? ridiculous suggestion

Never ever had a problem and have a FCU as a light switch in both my garage and shed for over 20 years used daily.

Ditto

 

[Taylortwocities]

A switch will be rated for several thousand ( if not tens of thousands ) of operations, An FCU may have a much lower rating.

MK quote
Operational testing (all plate switches): tested to 100,000 operations for mechanical life tested to 30,000 operations at 10 amp rating.

There's no specialswitch for an FCU plate.

 

[Murdochcat]

Not a good idea to use an FCU as an ON-OFF switch for a lamp ( or any other frequently used item ).

A switch will be rated for several thousand ( if not tens of thousands ) of operations, An FCU may have a much lower rating.

it’s miss information like this that causes problems

facts, facts, facts

 

[flameport]

There would also need to be a junction at about 60m out, splitting power to the summer house and greenhouse: that junction box would also need to be buried.

All cables should be installed in ducting. This will allow you to install the duct now, and the appropriate cables installed later.
It also allows for easy modification, replacement or addition of cables in the future.

If using a single cable, that cable should be taken to the first building, any connections made there, and then a cable to the second building, and so on. All joints/junctions would be inside the buildings and not concealed below ground.

If that cannot be done for whatever reasons, then take the ducting to a recessed access box and whatever joints are required can be done in that.
Example duct: https://www.plastics-express.co.uk/black-twinwall-duct-63mm-x50m-coil-p-pm400
Example access boxes: https://www.plastics-express.co.uk/ducting/duct-access-boxes

Can the same power cable be used to power 3 pin sockets and lighting, which is likely to be low voltage LED in the greenhouse at least.

Probably, but this is why you install the ducting, so that if more than one cable is required it's a simple matter to install it.
Rather than installing some cable today and then finding out later that it's not appropriate for what you want.

 

[ericmark]

What can be done, and what is advisable are not the same, I have made epoxy resin joints under ground, but these would always be tested before back filling, and the joints are no cheap.

It seems unlikely it would be ecomic to do this in your case.

Some one needs to sign to say they have designed the installation, so you need to select an electrician to design, he in turn can say will you dig the trench for me, but he needs to remain in control.

 

[Harry Bloomfield]

If using a single cable, that cable should be taken to the first building, any connections made there, and then a cable to the second building, and so on. All joints/junctions would be inside the buildings and not concealed below ground.

If doing that, for whatever reason, it is not a sensible option - then an underground T or Y resin joint can be used, for armoured cables.