YET another house to garage thread...

[TheoJones]

But there's a twist that makes it interesting, honest

just moved house, and I have a small outhouse roughly 5 metres from the main building, then the garage a further 30 metres on beyond that (35m as the cable goes, there's a duct involved to the garage).

power to the wee outhouse is shonky as get out just now, and I am replacing it, garage has no power just now - thinking I should use this as a good opportunity to do things right for the garage too.

My plan is...

Add a 40A MCB to the house CU, and run over 6mm 3-core SWA to the outhouse, tying the outhouse into the CU's Earth.

Have a small 2-way there, with a 16A RCBO for a couple of sockets (only expecting a freezer in there, possibly plugging a lawnmower in) and a 6A RCBO for lighting (never in a million years going to use more than half an amp, but hey ho...)

Then, bus the Live and Neutral onto a 6mm 2-core SWA onwards to the Garage to another 2-way, garage is a brick built affair, no external metal, but has water (copper back to the house). Planning to use an earth rod there.
Again, 6A RCBO for lighting circuit and a 32A RCBO protected ring on 2.5mm T&E

The thinking is:

Happy that there's spare capacity for a 40A MCB, because the house has a 100A supply, and we have put in gas central heating and gas hob, replacing storage heaters and a leccy hob.
Keeping the house earth for the outhouse as it's only 5 metres over nice fat conductors, and an earth rod would be a PITA where the outhouse is.
Using 6mm SWA where 4 would probably be okay just to over-engineer it a bit and get some margin in there.
No RCD protection in the main CU so you don't get into a situation with the thing tripped inside the house, and unable to reset it in the garage/outhouse, so protection at the edges instead.

I'm reasonably confident that this is okay, but this isn't my day job, so I'm cautious enough to want to get a proper set of eyes on this rather than kill myself/the wife/the neighbour's dog.

Any gotchas that I have missed?

Tj.

 

[malcolmsanford]

But there's a twist that makes it interesting, honest

just moved house, and I have a small outhouse roughly 5 metres from the main building, then the garage a further 30 metres on beyond that (35m as the cable goes, there's a duct involved to the garage).

power to the wee outhouse is shonky as get out just now, and I am replacing it, garage has no power just now - thinking I should use this as a good opportunity to do things right for the garage too.

My plan is...

Add a 40A MCB to the house CU, and run over 6mm 3-core SWA to the outhouse, tying the outhouse into the CU's Earth.

Have a small 2-way there, with a 16A RCBO for a couple of sockets (only expecting a freezer in there, possibly plugging a lawnmower in) and a 6A RCBO for lighting (never in a million years going to use more than half an amp, but hey ho...)

Then, bus the Live and Neutral onto a 6mm 2-core SWA onwards to the Garage Are you planing to parallel this SWA from the main switch on the 2 way board. I personally would run the SWA into an adaptable box, using a din rail and connectors, tail in the 2 way and then off to the garage. 2 SWAs into a 2 way board may be tight

to another 2-way, garage is a brick built affair, no external metal, but has water (copper back to the house). Planning to use an earth rod there.

Again, 6A RCBO for lighting circuit and a 32A RCBO protected ring on 2.5mm T&E Can I ask why a 32amp ring in the garage what are you expecting to use in their that would require this much power.

The thinking is:

Happy that there's spare capacity for a 40A MCB, because the house has a 100A supply, and we have put in gas central heating and gas hob, replacing storage heaters and a leccy hob.
Keeping the house earth for the outhouse as it's only 5 metres over nice fat conductors, and an earth rod would be a PITA where the outhouse is.
Using 6mm SWA where 4 would probably be okay just to over-engineer it a bit and get some margin in there.Think you may find that once you do you calculations, the original 6mm SWA sub main to the outbuilding may not be too much over engineering. Remember that cable is going to feed 2 installations, that both have lights and a distance of nearly 40mts. So you VD at the furthest point is only 3%, and for some reason your wanting a 32amp ring in that garage
No RCD protection in the main CU so you don't get into a situation with the thing tripped inside the house, and unable to reset it in the garage/outhouse, so protection at the edges instead.

I'm reasonably confident that this is okay, but this isn't my day job, so I'm cautious enough to want to get a proper set of eyes on this rather than kill myself/the wife/the neighbour's dog.

Any gotchas that I have missed?

Tj.

The installation seems fine. Just the above points to consider

 

[TheoJones]

Thanks mate -

So, yeah, the plan was to parallel the second SWA from the switch. Thanks for the suggestion - I was wondering how much of a physical issue there would be bringing those big connectors together.

On the 32 Amp RCBO, I was going for that because I thought it had to be a 32A RCD/RCBO for a ring main?

I'm assuming that a ring is safer than running radials, and more flexible for the future if I wanted to run a spur for something that wasn't thought of up front. Is that not really the case at this scale?

I'm planning to use the garage as a half wood working shop, half garage, but even still - wood working tools are nasty big draws (heaviest tool I have is 2Kw), but you can really only use one of them at a time. I expect that the most I would ever have going up there would be my big saw (another 2Kw), shop vacuum (1Kw) and a radio (bugger all...) So what, 13A tops? In my old house, I ran my whole workshop setup from a single 13A socket on a power strip, so...

I guess that's the problem with being a practised amateur - you pick up assumptions along the way that might not translate into this specific set of circumstances.

Just for the sake of clarity - my intention here is to do the work, then get an actual pro to check it over before doing the final connections at the house. I'd like to think I know my limits

 

[malcolmsanford]

Thanks mate -

So, yeah, the plan was to parallel the second SWA from the switch. Thanks for the suggestion - I was wondering how much of a physical issue there would be bringing those big connectors together.

On the 32 Amp RCBO, I was going for that because I thought it had to be a 32A RCD/RCBO for a ring main?

I'm assuming that a ring is safer than running radials, and more flexible for the future if I wanted to run a spur for something that wasn't thought of up front. Is that not really the case at this scale?

I'm planning to use the garage as a half wood working shop, half garage, but even still - wood working tools are nasty big draws (heaviest tool I have is 2Kw), but you can really only use one of them at a time. I expect that the most I would ever have going up there would be my big saw (another 2Kw), shop vacuum (1Kw) and a radio (bugger all...) So what, 13A tops? In my old house, I ran my whole workshop setup from a single 13A socket on a power strip, so...

I guess that's the problem with being a practised amateur - you pick up assumptions along the way that might not translate into this specific set of circumstances.

Just for the sake of clarity - my intention here is to do the work, then get an actual pro to check it over before doing the final connections at the house. I'd like to think I know my limits

To be honest the more you are telling us the more I would advise that you get some professional help with design for this. Your saying that you have wood working tools and the juiciest is 2KW, fair enough but are you thinking of heating this place in the winter? Making yourself a cup of tea in there ?

Ring Finals are fine and give you many options. But you could also install radials a 4mm 32amp radial could save you cable runs, again the design criteria is up to you

As your in Scotland you don't fall under the dreaded Part P, but I'm sure there must be certain conditions met about installations north of the border

 

[TheoJones]

Aye, you might be right there.

In my professional life I make a reasonably good living doling out advice, and more often than not, I make the most on contracts where the client decided not to listen to advice from people who knew better (or didn't seek it out in the first place).

at least I know that I am on roughly the right lines - that will help with the ole BS detector when I come to talk to someone about it and there's money on the table.

thanks for your time!

 

[Engineer54]

But there's a twist that makes it interesting, honest

just moved house, and I have a small outhouse roughly 5 metres from the main building, then the garage a further 30 metres on beyond that (35m as the cable goes, there's a duct involved to the garage).

power to the wee outhouse is shonky as get out just now, and I am replacing it, garage has no power just now - thinking I should use this as a good opportunity to do things right for the garage too.

My plan is...

Add a 40A MCB to the house CU, and run over 6mm 3-core SWA to the outhouse, tying the outhouse into the CU's Earth. You haven't stated what your supply earthing system is, ..is it PME/TNC-S perhaps that's why you want to use an earth rod, to save a bit of cash??

Have a small 2-way there, with a 16A RCBO for a couple of sockets (only expecting a freezer in there, possibly plugging a lawnmower in) and a 6A RCBO for lighting (never in a million years going to use more than half an amp, but hey ho...)

Then, bus the Live and Neutral onto a 6mm 2-core SWA onwards to the Garage to another 2-way, garage is a brick built affair, no external metal, but has water (copper back to the house). Planning to use an earth rod there.
Again, 6A RCBO for lighting circuit and a 32A RCBO protected ring on 2.5mm T&E

Why on earth (no pun intended lol!!) would you want to rely on an earth rod and RCBO?? Earth rods (TT system) should be your Last choice/resort, especially as you have a perfectly good earthing arrangement at your supply you can use!!

The thinking is:

Happy that there's spare capacity for a 40A MCB, because the house has a 100A supply, and we have put in gas central heating and gas hob, replacing storage heaters and a leccy hob.
Keeping the house earth for the outhouse as it's only 5 metres over nice fat conductors, and an earth rod would be a PITA where the outhouse is.
Using 6mm SWA where 4 would probably be okay just to over-engineer it a bit and get some margin in there.
No RCD protection in the main CU so you don't get into a situation with the thing tripped inside the house, and unable to reset it in the garage/outhouse, so protection at the edges instead.

I'm reasonably confident that this is okay, but this isn't my day job, so I'm cautious enough to want to get a proper set of eyes on this rather than kill myself/the wife/the neighbour's dog.

Any gotchas that I have missed?

Tj.

If you do have a PME/TNC-S earthing system at the house, then it would require a 10mm 3 core SWA cable to the garage to enable compliant bonding to the extraneous water pipe (extending the house equipotential zone). But if it's a straight TN-S earthing system you have, a 3 core 6mm SWA cable will be fine out to the garage!!!