Providing garage with power supply from external plug on house

[mickey83]

I want to draw an electrical supply from the back of the house and run it through the garden to the garage to power an internal light, couple of sockets and a security light.

I've made a few searches but cant be sure on the approach. Is it sufficeint to have an external fused spur on the rear of the house before the power is fed to the garage, do I need a mini breaker system in the garage also, or in isolation only without any fused spur?

Any advice or suggestions?

Thanks

 

[ban-all-sheds]

I want to draw an electrical supply from the back of the house and run it through the garden to the garage to power an internal light, couple of sockets and a security light.

You need to think about how far away it is, as voltage drop will need to be taken into account when sizing the cable, as will fault loop impedance (sadly the values in that chapter are now wrong - you'll need to refer to the current version of the Wiring Regulations for the latest ones). More on the latter topic here.

You also need to make sure you use appropriate cable, appropriately routed. The normal approach is armoured cable, which is buried at a suitable depth. You might be able to run it above ground to the garage, but you'd need a wall to fix it to, not a wooden fence.

Providing garage with power supply from external plug on house

One thing you definitely may not do is to have a length of flex with a plug on the end, snaking through the garden to the garage.

Is it sufficeint to have an external fused spur on the rear of the house before the power is fed to the garage

Yes.

Is the circuit RCD protected? If not, use an RCD FCU.

do I need a mini breaker system in the garage also

Pointless if it's all supplied by a spur. You'll need FCU(s) in the garage for the lights.

or in isolation only without any fused spur?

Unlikely to be OK, but possible. What sort of circuit will you be coming from? Ring or radial? What rating is the fuse/MCB?


Any advice or suggestions?

• [wiki]Electrics%3Abooks[/wiki]
  
  
• [wiki]Electrics%3AMCBtoCable[/wiki]
  
  
• http://www.tlc-direct.co.uk/Book/4.3.1.htm (all subsections)
  
  
• http://www.tlc-direct.co.uk/Book/4.3.11.htm
  
  
• http://web.archive.org/web/20070327014113/http://www.kevinboone.com/cableselection_web.pdf
  
  
• http://www.tlc-direct.co.uk/Technical/Charts/VoltageDrop.html <- Specify 2-core cable and PVC, even if that is not what you are using or it will make invalid assumptions.
  
  
• http://www.tlc-direct.co.uk/Book/5.3.1.htm
  
  
• [wiki]Electrics%3AMCB2[/wiki]
  
  
• http://www.tlc-direct.co.uk/Book/7.13.3.htm
  
  
• http://www.tlc-direct.co.uk/Book/8.1.1.htm
  
  
• [wiki]Electrics%3ASWA_gland[/wiki]
  
  
• http://electrical.theiet.org/wiring-matters/16/elect-inst-outdoors.cfm?type=pdf
  
  
• [wiki]Electrics%3APart-P[/wiki]
  
  The references above which are in italics are out of date. The principles are still valid, and you can absolutely learn valid things from them, but you will need to refer to the latest edition of the Wiring Regulations to get the correct data.

 

[JohnW2]

Pointless if it's all supplied by a spur. You'll need FCU(s) in the garage for the lights.

Do you feel that a second FCU for the lights would really be necessary? Cable-wise, the upstream 13A FCU would probably be fine; if there were any technical issue, it would be with the 'rating' of the light switch, but that probably wouldn't concern many people.

Kind Regards, John

 

[ban-all-sheds]

Or the "rating" of the luminaire(s). Or the MIs.

Given that switches will be needed anyway....

 

[ericmark]

I would use a switched FCU for lights, but yes under 16A there is no requirement for a fuse for lights. I would personally however fuse to 3A.

 

[JohnW2]

Or the "rating" of the luminaire(s). Or the MIs.

Do luminaires often have 'ratings' as regards the supply/OPD?

Given that switches will be needed anyway....

True - but, as a general rule we would discourage the 'unnecessary' use of two OPDs in series (if we decided that the second one was unnecessary).

Kind Regards, John

 

[Iggifer]

You could quite easily use a 20A switch for the lights rather than a 10/6a, and there's plenty of fluorescent battens that are rated ~16A+ so if you do it correctly, I don't see the need for a second FCU

 

[JohnW2]

You could quite easily use a 20A switch for the lights rather than a 10/6a, and there's plenty of fluorescent battens that are rated ~16A+ so if you do it correctly, I don't see the need for a second FCU

As I said - nor, personally do I (and, despite some people's views, my view would not change if we were talking about a 10A, or even 6A, light switch) ... and I'm not even sure that the postulated 'current ratings' of light fittings necessarily commonly exist!

Kind Regards, John

 

[Iggifer]

As I said - nor, personally do I (and, despite some people's views, my view would not change if we were talking about a 10A, or even 6A, light switch) ... and I'm not even sure that the postulated 'current ratings' of light fittings necessarily commonly exist!

This Thorn one does, but plenty of others don't specify a max Amperage. That's not to say you don't have to use common sense, but given that it doesn't give you a max rating, I think anybody would struggle to prove why you shouldn't install it on a circuit with a 13A OPD

 

[JohnW2]

This Thorn one does, ...

Maybe, but can one be sure what the "Max. 10A" (in "Max. 10A >140°C (EVA/Silicon) HO5G, HO7G / HO5S, HO7S") actually refers to?

... but plenty of others don't specify a max Amperage.

Indeed. I'm struggling to recall a case I've come across of one which did.

That's not to say you don't have to use common sense, but given that it doesn't give you a max rating, I think anybody would struggle to prove why you shouldn't install it on a circuit with a 13A OPD

Quite so. Provided only that the flex was up to it (in practice it probably wouldn't be), and although I would usually fit a 3A fuse, I would loose absolutely no sleep if, say, a plugged-in table lamp or standard lamp etc. had a 13A fuse in its plug.

Kind Regards, John

 

[EFLImpudence]

Quite so. Provided only that the flex was up to it (in practice it probably wouldn't be), and although I would usually fit a 3A fuse, I would loose absolutely no sleep if, say, a plugged-in table lamp or standard lamp etc. had a 13A fuse in its plug.

Glad to see you are learning.

 

[JohnW2]

Quite so. Provided only that the flex was up to it (in practice it probably wouldn't be), and although I would usually fit a 3A fuse, I would loose absolutely no sleep if, say, a plugged-in table lamp or standard lamp etc. had a 13A fuse in its plug.

Glad to see you are learning.

I'm not too sure why you say that - I can't recall a time when I would have said otherwise!

You are perhaps referring to my view that one might just as well use as small a fuse as is adequate for the load (hence I personally use a lot of 1A and 3A fuses) - but that doesn't mean that I would "loose any sleep" over, say, a 0.25A lighting load (with appropriate cable) which had, say, a '6A rated' switch, and which was connected via a plug with a 13A fuse.

Kind Regards, John

 

[EFLImpudence]

You are perhaps referring to my view that one might just as well use as small a fuse as is adequate for the load

I thought you were of the opinion that it was more than just "might as well".

 

[JohnW2]

You are perhaps referring to my view that one might just as well use as small a fuse as is adequate for the load

I thought you were of the opinion that it was more than just "might as well".

Not really. I do personally believe (and generally practise what I preach) that (even though one shouldn't have to) one "might just as well" use the fuse to give the maximum possible degree of protection to whatever is within the load (regardless of what current the cable could cope with), but I accept that this is generally not 'necessary', nor necessarily practised by a lot of people. We don't even necessarily have to 'obey' what MIs say about this any more.

Kind Regards, John

 

[AndyPRK]

You could quite easily use a 20A switch for the lights rather than a 10/6a, and there's plenty of fluorescent battens that are rated ~16A+ so if you do it correctly, I don't see the need for a second FCU

I think 20A switches are more expensive than an FCU though.