Garden Wiring - RCD Question

Hi Folks,

A friend of mine installed an outdoor socket and also run some cable up to my shed. I want to check with you guys that it is safe as I am not 100% sure on the RCD tripping method.

Inside the house is the standard wiring from the house CU. He drilled a hole through the wall and extended the wiring from inside the house to an external socket. The external socket is in a weatherproof box and is also an RCD socket (with test and reset buttons). I know that anything I plug into that socket is double covered as it has the RCD on that socket and also the house CU protecting it. The cable running up to the shed is running directly out the back of the new RCD plug socket (via buried armored cable) and there is a fuse in the shed with an on/off switch to control just the shed part.

Here is what I need some help to understand. The armored cable running up to the shed is coming straight out the bottom of the new outdoor RCD socket. I figure that this socket will only break for things plugged into it (the lawnmower or whatever), but it probably will not break for things running out the back of it (ie, the armored). Is that right - would an RCD plug break for things coming out the back of it (rather than plugged into it)?

He said that either way it doesn't matter as the armored is joining the normal household wiring in the back of this new RCD box, so the armored running to the shed is already covered by the household CU at the house end and a fuse at the shed end... if it happens to also break at the new RCD its a bonus but its not needed. Is this right?

Any guidance appreciated.

Will

You are correct that the cable to the shed will not be coming via the RCD in the new socket.

Does your house CU have an RCD protecting this circuit?

If it does, the RCD on the socket is unnecessary (and it's likely that the CU RCD will trip as well as or instead of the socket RCD if there is a fault).

If it doesn't, your shed is not RCD protected.

Thanks for the quick responce. I do not think my CU has an RCD. I figure there are three options now:

1) Plug a plug on the end of the house-side armored and just plug that into the RCD protected socket when I want to use the shed power. I quite like this option as its easy and means I can totally unplug the shed if I want, plus the shed and buried armored still gets RCD cover.

2) Put an RCD in the shed. This is the easiest option, especially if I just replace the current fuse-spur with an RCD enabled fuse-spur. However, this means the buried armored has no RCD protection. Is it acceptable to just have an RCD at the shed end, and have the armored protected by the CU breaker?

3) Put an RCD at the house end of the armored before it goes into the back of the new socket. Bonus over option 2 is that the buried cable is connected but it is more awkward to fit (awkward location).

Unless you guys tell me otherwise, I think option 1 might be the best option.


Thanks

I doubt you could fit a plug on a piece of armoured cable .Put up a picture of your house CU

No problem....

House CU (ignore the bit that says shed, this something that they took away when I bought the house and goes somewhere else): http://i.imgur.com/COjKrOe.jpg and this is the RCD Plug: http://i.imgur.com/PgLysfu.jpg

Edit: I just noticed that the house CU breakers say RCBO so I guess that they do have RCD protection. Not sure if this changes things?

yeah all circuits have RCD protection, so carry on as you were.

No point having the RCD socket other than likely it will auto trip in a power cut so if using something and you when in to reset power it would not auto restart until you pressed reset button. Also no point in having a RCD in the shed.

In general a RCD is designed to trip between 1/2 and full rated current so supplying one RCD from another we go three times bigger every time. So 10 mA is fed from a 30 mA which is fed from a 100 mA which is fed from a 300 mA and over 30 mA is for fire not personal protection.

AndyPRK said:

yeah all circuits have RCD protection, so carry on as you were.

Click to expand...

To elaborare each of your breakers is labeled RCBO. That means each one is a combined MCB and RCD.

Your outdoor socket should not be an RCD type.

AndyPRK said:

yeah all circuits have RCD protection, so carry on as you were.

Click to expand...

Thanks for this. Based on that, it is fine how it is and I do not need to do anything? Would this be within building regs (if I get someone out to certify it)

Thanks for all the input guys, really appreciate it.

Which rcbo controls the outside socket and shed?

AndyPRK said:

Which rcbo controls the outside socket and shed?

Click to expand...

Number 3, the sockets.

The c32

You should have a 13a fuse somewhere.

Or alternatively connected off the 16a mcb

winston1 said:

Your outdoor socket should not be an RCD type.

Click to expand...

Why?

AndyPRK said:

The c32

You should have a 13a fuse somewhere.

Or alternatively connected off the 16a mcb

Click to expand...

Why...if giving an answer you should explain, that way it proves you understand what you are talking about. The external RCD protected socket is fed from the internal ring main, this is protected by a RCBO that is a C32 as required by the Regs (well recommended by good practice) The external socket being fed from the protected circuit is not an issue and does not require fusing down.

The issue is the SWA feeding the shed...

DrJimFranklin said:

The issue is the SWA feeding the shed...

Click to expand...

I thought that was ok now? What do I need to do?