Hello everyone, this is my first post and I wonder if anyone can help me.

I'm about to embark on wiring up my shed and garden. I've done plenty of wiring in my house such as light fittings, extra sockets etc, but this is my first "big" project. I have my plan sorted, but I just want to run it by this forum to ensure what I plan is correct, legal and safe.

My father-in-law gave me the basic outline of a plan (he's a proper spark) and donated a load of armoured cable and I'm about to set it in motion, but he's away on a big cruise now so can't run my plan by him at the moment.

Originally when we made up the plan, I told him my existing consumer unit was full, so he told me I would either have to replace it with a new split board or alternatively, buy a small RCD protected CU and wire that into my main CU, then wire up to my shed from that second CU.

Now it transpires that I do actually have a spare way on my CU (which is not a split board). So, here's my plan.

The donated cable I can't really identify a size (because I'm too thick to work it out...) it's AEI BS5467 600/1000V 4-core cable with an overall diameter of 20mm - each core has a diameter of about 4mm, but each core is made up of 7 copper wires, each with a diameter of about 1mm - so would this be 6mm cable?

I plan on having 4 radial circuits on new a CU in my shed - 3 lighting circuits with 6A MCB's and 1 socket circuit 16A MCB.

The first radial lighting circuit will go out of the shed along the wall down the side of a side passage and will serve a 10A MK Weatherproof 1 gang 1 way switch which in turn will provide power to 3 x 60W bulkhead lights along the wall. The cable run to the switch will be about 7.5m then the lights are at 2.5m intervals giving a total radial length of 15m. I plan on using 1.0mm cable in conduit along the wall.

The second radial lighting circuit will purely provide for two overhead lights in the shed. Both are 60W lights with pull cords (reusing two bathroom lights that I have replaced). Total cable run will only be about 4m from the CU, so I plan to wire along the shed roof in trunking, again using 1.0mm cable.

I realise that there is nothing stopping me combining these two circuits but I'm happy to keep them separate for ease of maintenance and to in fact, make my cabling runs less complicated.

The third radial lighting circuit will employ 3 metres of cable through the shed wall to an MK Masterseal 2 gang 1 way 10A single pole weatherproof switch which will separately control a water feature from one switch (12W / 3A) and as many as 4 outdoor spotlights (50W each) from the other. From the shed CU to the switch I was planning on using 1.0mm cable. From the weatherproof switch to the position of the water feature / lights is about 15m and I will be utilising the 4-core armoured cable again for this run, terminating in some sort of junction box (not decided yet - any advice?). I'm hoping to utilise the two live wires separately for the two systems and sharing the neutral and earth. (i.e. L1 supplies to the fountain, L2 supplies to the 4 spot lights, N and E common) so that I can switch the lights and the fountain separately through the one cable run. Am I okay to do this?!?

Finally, the fourth radial circuit would purely provide a double socket, 1 will be used by a tumble dryer (which says on it 250W - 2900W MAX) and the other socket will be used for either a lawnmower 1.15kW or a strimmer 250W with potentially both sockets being used at the same time. I had initially planned to use a 16A MCB for that circuit, but according to the TLC calculator, there is a potential maximum load of 17.39A so should I use a 20A MCB for this circuit instead of the 16A? The cable run will be no more than 2 meters in trunking. I am planning on using 2.5mm cable here.

All of this would be protected by a 40A 30mA RCD (correct size given the information above?) in the consumer unit in the shed.

From the house to the shed I would be running about 8-10 meters of the 4-core armoured cable clipped to the wall. I am planning on attaching it directly to my existing house CU on the spare with utilising a 40A MCB - this is probably the part I am most unsure of - as two people have told me that I should have an RCD at the house end too which would probably entail exchanging my existing CU with a split board (or can I get a 1 unit width RCD to go in my existing CU and supply outside without having a split board CU??).  Two other people have told me that I don't need an RCD at the house end. This would be my preferred method, just an MCB protected circuit heading outside via the armoured cable to the shed CU which has the RCD protection. If someone could clearly lay out my options and the preferred solution to this part of the plan I would be very grateful.

Oh, I am also (on advice) considering that the armoured cable from the house to the shed stops just outside the shed at an industrial socket (such as http://www.tlc-direct.co.uk/Products/GW240slash63slash3S.html) then having a fly lead from that into the shed CU which would be about 2 meters cable - but I'm not sure what cable I would need to build this fly lead from - can't really find any flex that is heavy duty enough (can only find 4.0mm 32A flex) and twin and earth would be impractical for this... but the idea of being able to detach the shed and therefore also isolate the 4 circuits and the CU merely by removing the fly-lead has it's plus points. Any thoughts on this?

Well, that's a whole lot of text, but I hope it's a well-thought out plan. Any offers of advice or encouragement that the plan is sound would be great. Thanks for your time!

Adama

Hi
Just a few quick observations.
Sounds like your donated SWA is only 2.5 or 4mm at the most.
You should on no account use a 40A mcb to protect this from the huse CU. Stick to a 20A mcb at the most.

You mentioned using a common neutral to some of your sub-circuits - this is NOT permitted, unless it is done to run more than one light from the same switch or mcb.

Shared Neutrals are dangerous.

Good luck

TT

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This fly lead you want is from a CEE/C Form type industrial plug and socket?

For reference the plugs and sockets are coloured by voltage e.g.

Red = 400V
Blue = 230V
Yellow = 100V

You would want a blue plug and socket, these come in 16A\32A\63A, '32A' is really your only option

Twin and Earth cable is unsuitable for using on plugs, I suggest 4mm Flex, this would go well with your 32A plug and socket.

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There are two ratings on the RCD, one is a current rating, this is the current the RCD will take safely, this is 40A, however this does not mean the RCD will trip and 40A, it will just burn out because it is not like a fuse or MCB

The second rating is a trip rating, this is 30mA, 30mA is the standard rating for supplementary protection against direct contact, e.g. electric shock.

This RCD would be suitable, but don't treat it like a fuse, it must be combined with a fuse to protect the shed.


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Il leave that for trician to explain, however you should have no problem using a 4-cored cable for multiple controll, as long as it is served via 1 protective device, and nothing is a sub circuit from this.

protective devices = fuse/miniture circuit breaker etc

[quote author=ban-all-sheds  link=1098040520/0#5 date=1098108007]
I'm not sure he did tell you that - why would he tell you to wire a second CU in to your main CU as a way round the fact that your main CU was full?   Where would you connect it?
[/quote]

Well, this was floated as an option because I pulled a face at having to replace the CU - the idea being to add a little 2 way RCD protected CU (garage type) - effectively a split board made out of two CU's rather than being 1 unit - of course he did tell me that this wasn't a great idea but was possible (said it was possible to wire them correctly but at that stage I wasn't taking detailed notes). I just thought it would be a lot easier than replacing the CU. Of course, now that I find I have a spare way on my CU then this is no longer being considered.


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No, my house CU doesn't have any RCD protection.


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Admittedly, I do not have a micrometer, so I'm estimating using a rather scientific 30p plastic ruler!  


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Any suggestions?  


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Not a problem - is probably better anyway as I can have the sockets at either end of the shed then which would be more flexible for me.


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I do at the moment on a standard RCD plug adapter, but once I have my outside (shed) sockets, I won't need to do that any more.


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Well, I suppose I can isolate it easily enough at the MCB at the house - just saves me taking my muddy gardening boots off etc if I can isolate it from outside - though I guess I don't need to isolate it on a regular basis.

Thanks for your time, my plan is now getting nicely fine tuned.

Adama