Secondary RCD For Outside Plug

[Darrenm200]

I'm considering adding a waterproof outside socket and a feed to some mains exterior lights.

The plan is to feed two FCU's from a spur (2.5mm T&E) taken from the back of a plug in the kitchen (have checked that it is on the ring main) one FCU (13A) will feed the external waterproof socket using 2.5mm T&E the second FCU (3/5 A) will feed the exterior lights using 1.5mm T&E.

The exterior lights consists of four 60W brick lights built in to a wall that is about 3M from the back of the house. The lights will be wired back individually using 1.5mm T&E to a weatherproof junction box at one end of the wall, the T&E will buried in between the two leaves of the wall.

From the junction box 1.5mm SWA cable will used to run back to the exterior of the house to another weatherproof junction box to connect to the wiring fed through the house wall from the FCU.

Part P aside !!

Is there any major issues with what I am proposing to do ?
Also the ring circuit is already RCD protected in the CU would it still be good practice to use a waterproof socket with it's own in built RCD or is this over kill !!? - obviously a non RCD weatherproof socket is much cheaper.

All cables within the house will be run in the correct zone behind dry wall lining (will still probablly cap with plastic capping).

Sorry it's so long winded, all advice will be appreciated.

 

[JohnD]

The plan is to feed two FCU's from a spur (2.5mm T&E) taken from the back of a plug in the kitchen (have checked that it is on the ring main) one FCU (13A) will feed the external waterproof socket using 2.5mm T&E the second FCU (3/5 A) will feed the exterior lights using 1.5mm T&E.

1) When you say "plug" I hope you mean "socket"
2) You are suggesting taking two spurs off one socket. Take one spur. Put a 13A FCU on it. It will be preferable to use a RCD FCU. This gives you a fused spur. From this you can take a feed to your socket, and another to an FCU with a 3A fuse for your lights.

the T&E will buried in between the two leaves of the wall.

Don't run cables in the cavity. Use conduit or mini trunking and put the cable on the surface.

From the junction box 1.5mm SWA cable will used to run back to the exterior of the house to another weatherproof junction box to connect to the wiring fed through the house wall from the FCU.

You will find SWA difficult to work with. If you insist on it you will need to use steel boxes and brass glands.
Why do you want the complexity of junction boxes? Can't you just run from one lamp to the next?

 

[davelx]

2) You are suggesting taking two spurs off one socket. Take one spur. Put a 13A FCU on it. It will be preferable to use a RCD FCU. This gives you a fused spur. From this you can take a feed to your socket, and another to an FCU with a 3A fuse for your lights.

Interested why you suggest an RCD FCU, given that the ring is already RCD protected? Won't there be a discrimination issue?

 

[JohnD]

sorry, I missed that.

 

[securespark]

Secondary RCD? What's that all about?

 

[Darrenm200]

2) You are suggesting taking two spurs off one socket. Take one spur. Put a 13A FCU on it. It will be preferable to use a RCD FCU. This gives you a fused spur. From this you can take a feed to your socket, and another to an FCU with a 3A fuse for your lights.

Interested why you suggest an RCD FCU, given that the ring is already RCD protected? Won't there be a discrimination issue?

So basically your saying not to use another RCD in any shape or form as the ring main is already protected at the CU.

 

[Darrenm200]

Secondary RCD? What's that all about?

Basically I was asking if I spur an outside socket of a socket on the ring main if it was good practice to use an outside (waterproof) socket with it's own in built RCD, given that the ring main is RCD protected at the CU.

Or would this be overkill / incorrect.

 

[JohnD]

It will probably not help at all.

It will bring the added inconvenience that in the event of an earth fault, both will (usually) trip so you will have twice the work of resetting them.

The waterproof RCD sockets are ridiculously expensive, so I would generally prefer an RCD inside the house, which will protect the outside cabling and multiple fittings.

In some conditions, a house will have a 100mA Time delayed RCD, which is not fast enough or sensitive enough to protect outdoor sockets. In that case you need an additional 30mA 30mS RCD for sockets, and they will not trip together as the time delayed one is slower.

 

[Darrenm200]

The plan is to feed two FCU's from a spur (2.5mm T&E) taken from the back of a plug in the kitchen (have checked that it is on the ring main) one FCU (13A) will feed the external waterproof socket using 2.5mm T&E the second FCU (3/5 A) will feed the exterior lights using 1.5mm T&E.

1) When you say "plug" I hope you mean "socket"
2) You are suggesting taking two spurs off one socket. Take one spur. Put a 13A FCU on it. It will be preferable to use a RCD FCU. This gives you a fused spur. From this you can take a feed to your socket, and another to an FCU with a 3A fuse for your lights.

the T&E will buried in between the two leaves of the wall.

Don't run cables in the cavity. Use conduit or mini trunking and put the cable on the surface.

From the junction box 1.5mm SWA cable will used to run back to the exterior of the house to another weatherproof junction box to connect to the wiring fed through the house wall from the FCU.

You will find SWA difficult to work with. If you insist on it you will need to use steel boxes and brass glands.
Why do you want the complexity of junction boxes? Can't you just run from one lamp to the next?

1. Sorry i did mean socket not plug
2. Thanks for the advice on connecting the FCU's
3. Cable is already installed between leaves of wall not a cavity wall just a double leaf garden wall - did not want the mess of external conduit / not enough room to run conduit or trunking between leaves of wall.
4. SWA is being used only for the run from the house to wall as it's too be buried in the garden, i'll use brass glands but I dont see why I need to use metal boxes as I can maintain earth bonding via the earth tags on the glands.
5. At the wall end I've run individual T&E to each lamp i.e 4 runs, these will then all go back to one junction box on the wall to be connected to SWA cable.
Looping the lights together looked like a pain as the connector is external to the lamp body i.e the connections would be expossed inside the wall and not watertight, so thats why I've used individual runs of T&E that i will wire to the actual bulb holders inside each light.

Thanks for the advice

 

[Darrenm200]

The plan is to feed two FCU's from a spur (2.5mm T&E) taken from the back of a plug in the kitchen (have checked that it is on the ring main) one FCU (13A) will feed the external waterproof socket using 2.5mm T&E the second FCU (3/5 A) will feed the exterior lights using 1.5mm T&E.

1) When you say "plug" I hope you mean "socket"
2) You are suggesting taking two spurs off one socket. Take one spur. Put a 13A FCU on it. It will be preferable to use a RCD FCU. This gives you a fused spur. From this you can take a feed to your socket, and another to an FCU with a 3A fuse for your lights.

the T&E will buried in between the two leaves of the wall.

Don't run cables in the cavity. Use conduit or mini trunking and put the cable on the surface.

From the junction box 1.5mm SWA cable will used to run back to the exterior of the house to another weatherproof junction box to connect to the wiring fed through the house wall from the FCU.

You will find SWA difficult to work with. If you insist on it you will need to use steel boxes and brass glands.
Why do you want the complexity of junction boxes? Can't you just run from one lamp to the next?

John with reference to point 2 I was planning on running the spur from the existing socket to a 13A FCU for the outside socket and a seperate spur from the same existing socket to a 3A FCU to feed the lights, that way I can isolate the exterior plug but leave the lights operational. Is there any reason not to do it this way ??

I will actually take the feed for the 3A FCU from the feed (not load) of the 13A FCU to minimise the number of wires in the back of the existing socket.

Cheers Darren

 

[JohnD]

John with reference to point 2 I was planning on running the spur from the existing socket to a 13A FCU for the outside socket and a seperate spur from the same existing socket to a 3A FCU to feed the lights, that way I can isolate the exterior plug but leave the lights operational. Is there any reason not to do it this way ??

I will actually take the feed for the 3A FCU from the feed (not load) of the 13A FCU to minimise the number of wires in the back of the existing socket.

Cheers Darren

It is considered bad practice (and possibly not in accordance with regulations depending on how you read them*) to take two spurs from a single accessory.

The fused spur however is a very acceptable way to do it.



*this is a separate discussion point

 

[Darrenm200]

It will probably not help at all.

It will bring the added inconvenience that in the event of an earth fault, both will (usually) trip so you will have twice the work of resetting them.

The waterproof RCD sockets are ridiculously expensive, so I would generally prefer an RCD inside the house, which will protect the outside cabling and multiple fittings.

In some conditions, a house will have a 100mA Time delayed RCD, which is not fast enough or sensitive enough to protect outdoor sockets. In that case you need an additional 30mA 30mS RCD for sockets, and they will not trip together as the time delayed one is slower.

John,

I've checked the RCD in the CU it's a 80A ,32mA. It does not state on it the reaction time. The only other markings on it are Legrand, 086 31 & BS EN61008-1. Does this sound like it will be acceptable ??

 

[JohnD]

That is an ordinary one without time delay, it will trip in about 30mS though this depends on size of leak. Though I would expect it to say 80A, 30mA (not 32mA)

This is the kind of RCD normally used to protect outdoor sockets, electric showers and so on to give protections against electric shock, so (provided it is in working order - remember the regular tests) if it protects your outdoor socket, it is quite satisfactory.

 

[securespark]

Have to say that some RCD's are required to trip within 200ms, and others in 300ms. But John is right, most trip well before that. Unless they have never been operated and are mechanically sluggish...