Garage Supply Question

[lurchio]

Probably a straight forward one for you all, just a new concept to me.

House has a 3036 rewirable board. Old shower was on a 40amp breaker, no longer in use.

Garage (this is almost comical) is wired as a spur in 2.5 t and e off the house ring main. It goes to the garage and is running three double sockets and two fused spurs. (It stays as a radial in the garage. Garage is connected to the house.

My plan to make good is to put a 3 way consumer unit in the garage, rewire the sockets on a ring (32 amp breaker), light on its own (6 amp breaker) and alarm on its own (6amp breaker).

My plan would be to run a 10mm T&E to the second board off the 40 amp spare breaker. Would this comply? Does it take into account the size of the CPC with the adiabatic equation or does that not come into play? Thats the bit I'm slightly confused about. Cable run will be approx 7 metres, all within the property, no risk of corrosion or weathering.

In reality the 32amp breaker is excessive, six sockets and all that is running is a fridge, a freezer and a motorcycle charger, but it may as well be doubles rather than singles...

Thoughts??

 

[Marvo]

What is the earthing arrangement at the main house? Are you planning to extend the equipotential zone to the garage?

 

[lurchio]

Sorry forgot the new board with have RCD protection also.

TNS Supply

Im guessing as its pre 17th edition it will require the extension of the equipotential zone to ensure the new install complies??

Its not a special location nor is there any exposed conductive or extraneous conductive (maybe actually a waste pipe but that could be plastic) so should that be metallic that will require bonding.

 

[Sintra]

The sub main might require rcd protection depending on installation methods. Work out the size of CPU required using the adiabatic then you will know if it complies or not.

 

[lurchio]

I get 10mm when i work it out... so it would require an extra earth cable running with the 10mm t and e.

So to confirm, a 40amp breaker in the house, ran in 10mm t and e to the sub board which is rcd protected and runs separate 10 mm earth in, that would comply?

Knew i would get there in the end

 

[telectrix]

doesn't ring true. 10mm cpc would equate to around 3.6kA fault current assuming a disconnection time of 0.1sec.

 

[Sintra]

Doubt you would need a 10mm cpc. Can you show your working out of this. What is the installation method for the 10mm t&e?

 

[lurchio]

Had to break the books out for this one! Been a while!

s= I2 x t square over k.

Firstly i don't have Zs so working off max zs minus a few but it works.

Uo = 230volts
Max ZS is 1.66 so lets drop it to 150ohms
its a 3036 Semi Enclosed Fuse
Rated at 45 Amps
Single Cable not Bunched
Copper, 70oC Thermoplastic

so

I2 = 23510.09
K=143
Time is 5 seconds for a TNS exceeding 32A

2.4mm conductor would suffice, so running in a 10mm T and E which has a CPC of 4mm is fine!

That got the noggin ticking!

 

[Engineer54]

If the garage is connected, or is part of the main house why do you think it requires a supply all of it's own?? Either extend the original downstairs RFC, or provide a separate ring or radial from the new CU. For the lighting, just extend the downstairs lighting circuit out to the garage, if it doesn't already...

 

[Badged01]

In line with what E54 says, if the garage is part of the house (i.e. attached) then just extend the already existing circuits for light and power. Simplest option?

If you are still keeping the 3036 board and want a seperate CCU in the garage then the cable run to the garage may need RCD protection dependent upon how you install it. As to whether its 4, 6 or 10mm cable I'll leave you to do the calcs but dont forget the Cf factor! Also confirm that you have main bonding in place -- your not extending any zone but it will be need to comply with regs for the new circuit/CCU.

 

[Engineer54]

If you are still keeping the 3036 board and want a seperate CCU in the garage then the cable run to the garage may need RCD protection dependent upon how you install it.

I must have miss read the OP's post this morning, i thought he said he was intending to install a new house CU (c/w RCD's), but he was talking about a CU (that's not needed) for the garage!! lol!!

 

[lurchio]

Just wondering on others views more than anything!

How about this solution which makes life even easier.

Leave the 2.5mm in and use to to feed the sockets, there is room on the 3036 board so put a 20A fuse in and have that as a Radial sockets, Spur off for the alarm.

Then run a single 1mm in for the lights off a 5A fuse, that way only having to install one new cable and just a bit of rejigging in the garage?

 

[Brightspark2]

Why not just spur off for the lights too?...

Don't forget about the need for additional RCD protection on your sockets and possibly cable depending on installation method...

 

[Brightspark2]

Also how does the T+E get to the garage, is it correctly installed?...

 

[Engineer54]

Just wondering on others views more than anything!

How about this solution which makes life even easier.

Leave the 2.5mm in and use to to feed the sockets, there is room on the 3036 board so put a 20A fuse in and have that as a Radial sockets, Spur off for the alarm.

Then run a single 1mm in for the lights off a 5A fuse, that way only having to install one new cable and just a bit of rejigging in the garage?

Sounds like a real pig's ear of a job doing it that way!! Why not just do it right and do it once!!
Why you wouldn't change the existing CU for a RCD protected CU, is also a little worrying...

 

[jaypp]

after checking bonding etc complies, you could split tails to new board, leaving existing unaltered. I personally don't favour this as it's a 'work around' and means possible safety issues on existing are ignored/missed.


edit; i assumed (perhaps incorrectly) existing board was in garage

 

[Jay Sparks]

after checking bonding etc complies, you could split tails to new board, leaving existing unaltered. I personally don't favour this as it's a 'work around' and means possible safety issues on existing are ignored/missed.

But if the exciting install tests out fine.....why would you need to change it at all???
Only the new install, depending on the erection method may need RCD protection.
But you could mention the benefits of a new cu to the customer without putting pressure on them to change it.

Jay

 

[jaypp]

But if the exciting install tests out fine.....why would you need to change it at all???
Only the new install, depending on the erection method may need RCD protection.
But you could mention the benefits of a new cu to the customer without putting pressure on them to change it.

Jay

you wouldn't. and no need to test existing either. as i said, personally don't like it

 

[Jay Sparks]

you wouldn't. and no need to test existing either. as i said, personally don't like it

I would rather change the exciting cu also but that's not always necessary. If the new install cable to the new cu was clipped direct, then it may not need rcd protection!!
But as you say, need to check for main bonding.