House to garage to shed

[graham964]

Hi

The current installation I have is based on a 16A RCB with an RCD rated at 30mA from the CU in the house to the garage. The SWA cable used for this 10m run underground (tarmac) is 1.5mm CSA and it terminates in another non RCD CU which has three wire fuses one for lighting rated at 5A, a second for external lighting rated at 5A and one for two double sockets (not a ring) rated at 15A.

From the garage CU a 2.5mmCSA SWA cable passes underground to the existing shed a cable run of approximately 10m. The connection in the garage for the shed is simply wired into the CU 2 pole switch.

The termination in the shed is a FSB which gives a supply to one 13 double socket and a strip light.

All of this was done professionally probably about 20 years ago and it all looks very neat and was done before I moved in.

I did some electrical work in the house about 5 years ago which included fitting a new CU, new ring, three way lighting circuit, cooker and hob points. All of which I had certificated/tested by a registered electrician. The rest of the house was also tested which included the aforementioned garage/shed installation. No faults.

Unfortunately the strip lights in the garage have developed a problem and regularly trip the RCD in the house (PITA). Consequently I have decided to replace the CU in the garage for a new unit which I am confident that I can do and move the supply from the house CU to the non RCD side of the CU (it is a split CU). I also have a new shed which is about 30m away which I have calculated for a 5% voltage drop can be done with 2.5mmCSA SWA, the load will be small a lighting circuit and a single powerpoint. (The old shed will be removed with all of its wiring)

There are two issues with doing this, I will have to find another electrician to certify my work as my friendly electrician has moved away and changing a CU is a Part P job. The other is that the cable run from the garage to the new shed is going to require a lot of effort to bury the cable, given the cable is armoured is there any way I could run it along a fence at its base or put it in a conduit on the base of the fence or surface.

Have I missed anything with this proposed job, I would appreciate feedback before I start.

 

[RF Lighting]

Why do you think you need to replace the supply cable? A 2.5mm² cable on a 16A circuit breaker is fine for a non workshop type garage supply of that length.

 

[ericmark]

The person designing needs to consider the best route. It is not something which can be done remotely it needs who ever is going to sign for design to do what they say they are doing and design.

This also includes working out earthing methods and volt drop.

I get volt drop to garage as 4.4 volts with a further 7.8 volt drop to new shed so 12.2 volt total expected loop impedance 1.145 assuming same size earth as line. For power should be less than 11.5 volt (5%) lights 6.9 volt (3%) so it would not comply.

Using lights able to handle the volt drop even if it does not comply it will likely not be a problem but getting any one to sign when it does not comply is going to be hard.

I am assuming you live in Wales as you say requires Part P notifying? Somerset I thought was in England in which case not notifiable as not a new circuit.

 

[ban-all-sheds]

Compliance with Part P and notification are entirely separate issues.

 

[winston1]

Why do you think you need to replace the supply cable? .

Could it be because the existing 10 metre run won't stretch to 30 metres?

 

[ban-all-sheds]

Have I missed anything with this proposed job, I would appreciate feedback before I start.

Find your electrician before you start, agree with him what he is happy for you to do, ask him all of the questions, and carry out the work under his guidance, or you will not be able to find one prepared to certify your work.

 

[graham964]

Thanks for the feedback. Power to the new shed is starting to sound awkward. Is there a good product (battery driven) for just lighting?

cheers

Graham

 

[ban-all-sheds]

Why is it awkward?

Nothing wrong with your original plan

I will have to find another electrician to certify my work

provided you get one lined up before you do the work.

 

[ericmark]

Go to any caravan shop loads of options. The problem is with a lead acid battery they are damaged if left flat. But use a small solar panel and that problem is solved.