External power supply to outbuilding

[Qooloo]

​I want to power up my shed that is 30m away, it will have a light inside and two outside, I will have a separate consumer unit fitted and will have 4 sockets. I have 6mm steel armoured cable, can I surface mount it to my fence or does it have to be buried? Please help.​

 

[Guest123]

Is it your fence?? Is it likely to be romoved/replaced in the future?? i.e, is it in a bad state of repair??

 

[johnhainsby]

hi there if it's your fence,just clip the cable to it,when you bring the cable into your shed,leave a couple of metres slack for possible use in the future,then if you decide to bury the cable you have enough slack cable to do this,also dont forget to install an r.c.d. device to protect this circuit.

 

[HandySparks]

dont forget to install an r.c.d. device to protect this circuit.

A distribution circuit in SWA doesn't have to be RCD protected, unless required because the supply is TT. In fact, it's usually better to put the RCD in the DB at the load end, supplying the final circuits.

 

[Qooloo]

Thanks for the quick responces, The fence I will be replacing too. I will have a RCD fitted. My main concern was that I would like to surface mount the cable but was not sure that it was permitted. But it seems perfectly acceptable?

 

[GLENNSPARK]

so,...what are the earthing arrangements here then?....

 

[oldtimer]

I changed a DB last month and there was a garage / workshop at the bottom of the garden about 25 metres away the supply cable was 6mm run in galvinised counduit fixed to a stone wall and I fitted a RCBO at the CU in the house and upgraded the garage DB to MCBs . The customer asked why did you not fit the RCD protection in the garage and I said because the supply cable would not be covered by it so this is my preference.

Also to me it does not matter if the garage is attached or 10 metres away I always advise a seperate RCBO /RCD fitted in the house

 

[GLENNSPARK]

I changed a DB last month and there was a garage / workshop at the bottom of the garden about 25 metres away the supply cable was 6mm run in galvinised counduit fixed to a stone wall and I fitted a RCBO at the CU in the house and upgraded the garage DB to MCBs . The customer asked why did you not fit the RCD protection in the garage and I said because the supply cable would not be covered by it so this is my preference.

Also to me it does not matter if the garage is attached or 10 metres away I always advise a seperate RCBO /RCD fitted in the house

but if a TN system...and run in SWA...or an earthed mettalic covering...then no RCD is required at the supply end.....otherwise its a high integrity C/U or a stand alone C/U with a 100mA s type...for discrimination....30mA in the outbuilding/shed/garage whatever....starts getting expensive.....now i know cost is always secondary to safety and compliance but......

 

[oldtimer]

but if a TN system...and run in SWA...or an earthed mettalic covering...then no RCD is required at the supply end.....otherwise its a high integrity C/U or a stand alone C/U with a 100mA s type...for discrimination....30mA in the outbuilding/shed/garage whatever....starts getting expensive.....now i know cost is always secondary to safety and compliance but......

Yep I agree with your point on cost and yes I forgot to mention that my selling point if you like to a customer is you have a split CU with 2 RCDs and you are only as strong as your weakest link so because the garage is external to the house I recommend that you have a 3 way rcd board in the house so that if there is a fault with the garage then it will not affect the house

 

[Qooloo]

so,...what are the earthing arrangements here then?....

Do I need any specific earthing? I was going to just earth the armouring? I have the shed supply coming from a B40 mcb fed from a RCD in the house, then I was going to fit another RCD in the shed feeding the mcb's for the sockets and lighting?

 

[Octopus]

Do I need any specific earthing? I was going to just earth the armouring? I have the shed supply coming from a B40 mcb fed from a RCD in the house, then I was going to fit another RCD in the shed feeding the mcb's for the sockets and lighting?

Do you have any training or competence with Electrics?

Have you consulted your schemes technical support?

 

[GLENNSPARK]

Do I need any specific earthing? I was going to just earth the armouring? I have the shed supply coming from a B40 mcb fed from a RCD in the house, then I was going to fit another RCD in the shed feeding the mcb's for the sockets and lighting?

if a TN system....then you can use an SWA to feed the shed/outbuilding straight of an MCB....although 40A seems a bit big to me....think about it....you will have typically a 6A for your lighting circuit in that outbuilding...then theres your outlets....so lets say a 16B type MCB for that...so where you got 40A from?....what CSA is the armoured you plan use?...3 core?....if a 3 core you can use one of the cores as a CPC...parrallel that up with the armouring......now, if its a TT earthing then you will need an upfront RCD for that armoured.....so you will be looking at a 100mA time delayed (for discrimination).....then you use a 30mA at the C/U in the outbuilding...for compliance with BS7671.....and it dont stop there either....is there any extrainious-conductive parts in this outbuilding? Gas and water pipes?....you could find yourself exporting a PME here...and if you cant understand about whether an upfront RCD is required ...or not together with what size MCB to use in relation to max demand and cable CSA......