Shed consumer unit

[dward49]

Hi guys and girls,

I'm newly qualified and want to confirm my method is sound before I commence any work. I'm registered with my CPS so can notify new circuits in domestic.

I have a new customer that has asked for lighting and power to the garden shed (wood construction). The existing installation is an economy 7 setup, with 2 consumer units. The 24hr CU is a MK Sentry (Plastic) Dual RCD split board with no free ways. Supply is TN-C-S PME, no supplier isolator fitted. Bonding in place. E7 night rate CU is earthed via 24hr CU, 24hr CU to cutout.

The shed is approximately 12m from the house. The ground between the house and the shed is concrete, with no damage to be made to it.

The plan in brief:

• Isolate DNO supply by pulling fuse - (my DNO permits this with scheme membership).
• Replace existing henley block for 5 way DP to enable additional feed
• Install MET & connect to cutout. From MET to both existing CU's and confirm readings.
• Install Fused Switch (Lewden FS) via Henley
• Fused Switch to 6mm T&E, through wall to Wiska adaptable box.
• Wiska adaptable box to 6mm 3 Core SWA.
• SWA will run via a catenary wire to shed, then clipped direct and brought into shed. At this point, I'll either use another adaptable box and move back to 6mm T&E or bring the SWA into shed and into lewden consumer unit.
• Shed CU (63A RCCB, 16A MCB, 6A MCB) will provide lighting radial and power radial, installed within flexicon and metal sockets.

The shed/workshop is used quite a bit, but with no extreme power requirements. Sewing machine, lighting, electric heater.

I've attached a few photos and a sketch to give an idea - apologies, I'm no artist!

D.

 

[Gavin John Hyde]

6mm swa seems a bit overkill for the proposed use given its only 12m.. 15 if from cutout.. Especially given its intended use.
You considered h07 or hituff? May find it easier to run from the cutout to shed in one go without joins. Why did you choose 6mm?
There is the nuisance if RCD in the house trips when in the shed but why not just run a rcbo radial from house via cat wire and use a fused spur of the radial for lights. It can double up as switch too.
You can take out a circuit from the main house cu, then use the unprotected spare way to supply a small board in house next to it. Incorporate the removed circuit plus the new rcbo. No board in shed, no switch fuse and smaller cable.

 

[buzzlightyear]

put a two way board maybe a garage unit rcd protected rcd mains switch and put a 20 amp. 4mm for the loading and go on from there .

 

[dward49]

Hi Gavin,

6mm is overkill, but to be honest, I have quite a bit of surplus that is just sitting there gathering dust so it's not being factored in as a cost item.

There are no unprotected spare ways in the existing board. Both splits are RCD protected and all circuits in use - I know a couple in the photo aren't actually labelled, but they are used elsewhere for circuits she's had added in the past.

The reason behind the shed CU is for possible expansion later. The lady (late 60's) has plans to expand her shed for her home business, garden lighting and decking area at some point, so this seemed to be a better idea for future proofing. (in hindsight, it may or may not be).

I may well be overthinking this.

D
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Hi Buzz,

Sorry I missed your reply. With the plans she has, I'd just prefer to make it easier in the future if that makes sense as this could potentially lead to further works down the line.

D

 

[buzzlightyear]

if the customer is going to expand then a sub board would be better to the shed and rcd in shed

 

[dward49]

if the customer is going to expamd then a sub board would be better to the shed and rcd in shed

That's exactly what I was hoping to achieve with my first plan using the shed/garage CU in there.

D

 

[buzzlightyear]

you have put on here a fuse switch .
Put in a sub board two way one a poss 32 amp 6mm cable job done .

 

[dward49]

you have put on here a fuse switch .
Put in a sub board two way one a poss 32 amp 6mm cable job done .

Hi Buzz,

Yes, I'm not sure if it's late and I'm getting confused!

A fused switch (probably a 63a SP&N Fused Switch) to a sub board in the shed via the 6mm. I'm thinking it takes up less real estate in the utility room than another sub board, even a garage CU, going to a the shed CU.

Can you explain the benefit of using a sub board over the Fused Switch for my own experience?

Thanks,

D

 

[davesparks]

Can you explain the benefit of using a sub board over the Fused Switch for my own experience?

There is no benefit, in fact it is better to protect a distribution circuit with a fuse than an MCB.

I would advise against using SWA on a catenary wire, a flexible cable would be far more suitable as the cable will be constantly moving in the wind, and the extra weight of the armour will add unnecessary stress to the fixings of the catenary wire.

I also would not be jointing the cable to T&E, unnecessary joints in a brand new circuit are just adding potential points of failure.

 

[telectrix]

ans your 6.0mm cable should be protected by a 40A SwF. not a 63A. other than that, I agree with davesparks. use a flex. cable if on a catenary.

 

[dward49]

ans your 6.0mm cable should be protected by a 40A SwF. not a 63A. other than that, I agree with davesparks. use a flex. cable if on a catenary.

Okay,

I've had a chat with the customer this morning and now have the option to re-purpose an existing RCD protected way within the current consumer unit as the circuit used is not needed.

Given that the installation for the shed as is, will only provide for lighting and power, she's content that the expansion plans may not happen until late into this year, this may well be the best way to go.

So considering the advice given above on cables, I'm now considering running HO7RNF 3-Core 4mm, to the shed from a 16A MCB into an adaptable box for socket radial and taking a switched fused switch spur 3A, to the lighting.

Make things easier?

D

 

[davesparks]

So considering the advice given above on cables, I'm now considering running HO7RNF 3-Core 4mm, to the shed from a 16A MCB into an adaptable box for socket radial and taking a switched fused switch spur 3A, to the lighting.

Make things easier?

D

I'd suggest a 20A circuit, at 16A you're cutting it a bit fine if someone plugs heater in whilst they are in the shed.

Why have you chosen flexible conduit for the wiring inside the shed? Does it need to be flexible?

 

[dward49]

I'd suggest a 20A circuit, at 16A you're cutting it a bit fine if someone plugs heater in whilst they are in the shed.

Why have you chosen flexible conduit for the wiring inside the shed? Does it need to be flexible?

Hi Dave,

The flexible conduit is purely cost related. I've got about 70m worth going spare and as the lady in question really doesn't have much money, I'm not charging her for it. This job will only be costed for the catenary wire and H07, plus a couple of brews and perhaps a set of trousers taken up!

I'm surprised no one has jumped in saying I need to TT the installation yet

Thanks,

D

 

[westward10]

People who mention TT for your scenario are taken out the back and shot.

 

[davesparks]

Hi Dave,

The flexible conduit is purely cost related. I've got about 70m worth going spare and as the lady in question really doesn't have much money, I'm not charging her for it. This job will only be costed for the catenary wire and H07, plus a couple of brews and perhaps a set of trousers taken up!

I'm surprised no one has jumped in saying I need to TT the installation yet

Thanks,

D

I don't understand how using flexible conduit helps with the cost of the job?
Using flexible conduit for surface installation just looks rough in my opinion, why not just use T&E clipped direct?

Why would anyone mention TT?