Garden electrics - extending existing outdoor socket

[samm1978]

Hi guys

Just trying to work out my costs and what to order before approaching an electrician. He's a rmate doing me a favour so wanted to make sure everything was here before he comes to do the work so I dont take up too much of his time. Was hoping you could help.

Basically I already have an existing exterior socket on its own ring - currently connected to the main house consumption unit.

I wanted to get

- light and a socket to my shed (for mower) at the other end of the garden (13m away)

- power to a mains powered water feature and some low voltage spike lights close to the house

I was wondering if the solution below would be suitable:

Untitled

• samm1978
• 26 Mar 2014
• 1

Any advice would be greatly appreciated.

 

[winston1]

Hi guys

Just trying to work out my costs and what to order before approaching an electrician. He's a rmate doing me a favour so wanted to make sure everything was here before he comes to do the work so I dont take up too much of his time. Was hoping you could help.

Basically I already have an existing exterior socket on its own ring - currently connected to the main house consumption unit.

I wanted to get

- light and a socket to my shed (for mower) at the other end of the garden (13m away)

- power to a mains powered water feature and some low voltage spike lights close to the house

I was wondering if the solution below would be suitable:

Untitled

• samm1978
• 26 Mar 2014
• 1

Any advice would be greatly appreciated.

You don't need the first FCU, the garage CU provides protection.

 

[dhutch]

Either I am miss-reading this, or you have a wire (or two) coming from the House CU, into a junction box, on to a single gang socket, out to and FCU for some light, over to another FCU for a water feature, round in swa to a third FCU, with swa to the garage, and then back into the first junction box.

It makey not sensey!


Daniel

 

[EFLImpudence]

Yes, the routing and choice of accessories are a bit of a shambles.

 

[Taylortwocities]

There's no point having a consumer unit in the shed if it is fed from a 13amp FCU. When do you think the 16amp MCB in the shed would trip? NEVER!!

And this 2.5mm SWA. How would this be routed to the shed?

 

[JohnW2]

There's no point having a consumer unit in the shed if it is fed from a 13amp FCU.

Agreed.

When do you think the 16amp MCB in the shed would trip? NEVER!!

"Never say never" (let alone shout it ) - and particularly not when talking about discrimination between two OPDs which differed by In by only about 25% !!

Kind Regards, John

 

[Taylortwocities]

BS60898 Type B 16A MCB versus 13A BS1362?

very unlikely

Hmm, where's me charts…….

 

[JohnW2]

BS60898 Type B 16A MCB versus 13A BS1362? very unlikely Hmm, where's me charts…….

You surprise me - I though we'd all seen situations when a 13A BS1362 in a plug had survived when a B32 (rather than a mere B16) had operated?

Whatever, even if your 'very unlikely' is right, I still stick to my "Never say never" Just about the first thing I was taught at uni was "never say 'never', 'always', 'all', 'none' or anything like that" - and that principle was often my salvation in multiple-choice exams over the years!

Kind Regards, John

 

[Aragorn84]

The B16 in my workshop trips out if i try to start my compressor in there. Every time, without fail.

The 13A fuse in the plug is fine, and it all works fine when connected to the 32A ring in the kitchen.

I presume the startup current of the motor is high enough to trip the magnetic part of the B16, but of a short enough duration that the fuse handles it just fine.

 

[JohnW2]

The B16 in my workshop trips out if i try to start my compressor in there. Every time, without fail. ... The 13A fuse in the plug is fine, .... I presume the startup current of the motor is high enough to trip the magnetic part of the B16, but of a short enough duration that the fuse handles it just fine.

Quite so. Despite TTCs view (presumably based on his experience), it's something I've personally seen happen plenty of times, and I have heard of it happening countless times.

It might, of course, not necessarily be that the duration of the start-up current (if allowed to continue) is too short for the fuse to blow - it could be that the rapid operation of the magnetic part of the MCB shortens the duration of the current to the extent that the fuse doesn't operate.

... but, of course, sometimes the 13A fuse does operate first, so there just aren't any certainties!

Kind Regards, John

 

[Aragorn84]

In this case, the same fuse doesnt blow on the 32A ring, so the current profile is clearly such that the fuse deals with it, but the breaker does not.

I guess its possible though that like you say, a fault current large enough to pop the fuse would be "stopped short" by the breakers faster reaction.

To be fair, the compressor is a 3HP unit and shouldnt be on a 13A plug at all, but it seems to work fine, and its somewhat more convenient to have it on a 13A plug than a commando.

I suspect once i sort the garage electrics out properly, i'll put a dedicated outlet in for it.

 

[JohnW2]

In this case, the same fuse doesnt blow on the 32A ring, so the current profile is clearly such that the fuse deals with it, but the breaker does not.

Fair enough.

To be fair, the compressor is a 3HP unit and shouldnt be on a 13A plug at all, but it seems to work fine, and its somewhat more convenient to have it on a 13A plug than a commando.

Sure, but that's not the point. We're talking about discrimination (or the reverse/lack of it) when current exceeds the rating of the fuse, whether that excessive current be due to a fault or to 'naughtiness' in what load one connects to the circuit!

Kind Regards, John

 

[samm1978]

Either I am miss-reading this, or you have a wire (or two) coming from the House CU, into a junction box, on to a single gang socket, out to and FCU for some light, over to another FCU for a water feature, round in swa to a third FCU, with swa to the garage, and then back into the first junction box.

It makey not sensey!


Daniel

I should explain my thinking better -

The bit on the diagram that says House is basically the outside of the kitchen wall - it's currently got an exterior double socket on it that's on it's own ring straight to the main house CU. The bit that says Shed is right at the back of the garden.

On the house wall
1. I want to extend the existing ring but I figured to do that I would first need to replace the double socket with a junction box.

2. I wanted a single power socket

3&4. I wanted to be able to turn the water feature and lights off independently - hence the separate FCUs for these.

5 - I didn't want to run two 13m lengths of SWA to the shed which is why I want to terminate the ring at this FCU at the back of the house. From here I intend to route one 13m length of SWA along the garden wall (above ground) to the CU in the shed. This also give me the added benefit of being able to switch all electrics in the shed off from near the house.

In the shed
6. I intend to connect a light to the 6a and put the socket on the 16a on a radial circuit.

All work will be done by a qualified electrician but as its a mate doing me a favour I wanted to make sure I have everything in place and was clear as to what I wanted so as not to take up too much of this time.

Any advice would be appreciated.

Untitled

• samm1978
• 27 Mar 2014
• 1

 

[Aragorn84]

Are you trying to incorproate the Shed FCU and the other two FCU's INTO the ring?

Your drawing shows a loop from shed FCU round to the feature and lights fcu's then back into the socket.

Seems daft to me to extend a ring final outside and back in again?!

 

[samm1978]

Are you trying to incorproate the Shed FCU and the other two FCU's INTO the ring?

Your drawing shows a loop from shed FCU round to the feature and lights fcu's then back into the socket.

Seems daft to me to extend a ring final outside and back in again?!

Yes - This ring already goes out and then in again - it is dedicated for the garden - it does not have any internal fixtures on it. It currently just powers an outside socket.

I guess you're saying it should have been on a radial?