Outdoor Power Questions

[ingleton1]

Hi, I am not an electrician but do intend to get one to do this work. What I'd like help with is confirmation or correction of my understanding so I can have an informed conversation with potential contractors.

Firstly - I want a double socket fitted on the side wall of the house to serve the patio for lawnmowers etc. There is a ring main socket on this wall so can they simply drill through the wall behind this socket and fit an IP66 RCD protected socket? If I wanted this socket higher up the external wall than the interior one is what should they be doing to protect the cable running up the outside wall? There is no RCD in the CU but the ringmain has a 16A MCB on it.

Secondly - I have a shed about 8m from the house. It has a couple of lights and sockets that are connected by a buried (no idea how deep) SWA cable, a tatty junction box and some mains cable to a dedicated 16A MCB in the CU. I'm concerned at the lack of an RCD so, here's my thinking. I need a garage CU installed in the shed. 30mA RCD, 16A MCB for the sockets, 6A MCB for the lights. They reuse the SWA cable (properly earthed with glands into IP66 enclosures at both ends this time) but I don't know how they should get from the IP66 box at the house end of the SWA to the CU. I think that at least the mains cable need rerouting (it goes in via an airbrick at the moment) but whatever they do it will still be a hole in the wall so what material difference is there?

Am I missing anything or does the above seem OK? Thanks in advance for your help. If this post isn't appropriate please let me know.

 

[Mr Mike]

Hi ingleton and welcome. You say your not an electrician, I must compliment you on your terminology, very good.

 

[chrish_1977]

Just reading what you have said you really need to get an electrician in, regardless of whether you want to talk technically with them, you have highlighted some things which could be wrong with the way the items you have mentioned are installed. Don't want to scare you but a ring should be on a 32 amp breaker ( if it is a ring of course), the shed should be have an rcd and any outside socket should also be rcd protected. Please correct me if I'm wrong too guys

 

[RJT_94]

as chrish_1977 said RCDs should also be required for your ring main/s in your house too

 

[telectrix]

RCBO on the house socket circuit. RCBO feeding the shed if cable from CU to outside needs protection. then no need for RCD in shed. everything protected.

 

[ingleton1]

So I guess the RCD requirement came in after the CU was fitted. Do you just swap out the MCBs with RCBOs then & not have RCDs on the outside sockets and in the shed CU? Do I even need a shed CU? They seem to come with RCDs already fitted which I don't understand if circuits are supposed to be RCD protected in the main CU. Why would you need two on a circuit?

 

[telectrix]

you don't need or want 2 RCDs on a circuit. it's optional whether you fit the RCD at source or at shed, depending on whether or not the feed to the shed requires RCD protection or not. fitting RCBO in place of MCB is easy. only problem is if there's a latent earth fault on the ring, then you have to find the fault and fix it when fitting RCBO, or any form of RCD.

 

[RJT_94]

Your best getting a spark in to look at your install and your requirements and then they will be able to come up with the best idea. but you wouldnt normaly install 2 rcds 1 down stream from another as you wouldnt get discrimination between the 2 (either could trip) i normaly only use one in the main cu to cover the shed and its supply circuit but diffrent factors affect this. What board have you got in out of intrest?

 

[ingleton1]

Not sure I'm answering your question but it is labelled up Proteus. Has 1 main switch & then a series of what I had always assumed to be MCBs but I suppose could be these RCBO things. How would I tell? Need a Spark don't I?

 

[Octopus]

For your outdoor circuit(s) just ask the sparky to include double pole isolation so if you get tripping you will be able to "isolate" the outdoor circuits by flipping the switch. So many times I do fault finding and it turns out to be the outdoor stuff affecting the house.

IMHO double pole isolation should be MANDATORY for all outdoor circuits.

 

[RJT_94]

look at what you think are mcbs and anywere on the fronts of them do they have 30mA wrote on them or a little test button?

 

[telectrix]

a test button would be as clue.

 

[ingleton1]

Yeah, got to the button about 2 secs after I posted the dozy question. Sorry. Still, at least I was right about them being MCBs.
So I should have the ring mains on 32A RCBOs whereas they are currently on 20A MCBs & they could then take a spur off that ring main for an external socket that wouldn't need an RCD.
For the shed I should have a dedicated RCBO & then there is no need for CU in the shed. That would then make the shed some sort of radial circuit wouldn't it?

 

[RJT_94]

so all the devices in the cu have test buttons? if so then they are rcbos

 

[telectrix]

ifr you have 20A MCBs on the socket curcuit/s they could be radials. need to determine if they are radials or rings before selecting protection devices.