Garage electrics

[daphantom]

Guys

Im installing the "famed" screwfix CU in my garage. Can i use 2.5mm SWA or does it have to be 4mm? I will be putting 4 doubles on the socket circuit + 5 downlighters on the lighting circuit. Also, I have an unused shower fuse of 30A beside my CU in the house, is it ok to use this for the supply to the new CU or is it too handy to be true?

Thanks

 

[RF Lighting]

How long is the run from the house to your new CU position?

 

[daphantom]

How long is the run from the house to your new CU position?

5 metres mate

 

[securespark]

2.5 not rated highly enough for 30A circuit.

 

[daphantom]

2.5 not rated highly enough for 30A circuit.

Thought so

Whats my best bet at the house CU end then?

 

[Taylortwocities]

At the house end you go to your computer and access http://www.competentperson.co.uk/search.asp

Type in "Antrim" and choose a friendly looking one.

 

[ban-all-sheds]

Part P she no apply in NI, so I don't suppose many electricians register....

 

[Taylortwocities]

That may be the case but (strangely), you get 63 registered sparks if you type "Antrim" into the seach feature

Still probably his best route for sucess..

 

[securespark]

2.5 not rated highly enough for 30A circuit.

Thought so

Whats my best bet at the house CU end then?

That's the wrong approach!!

Your method starts with, "I have 2.5mm² SWA, what's the maximum number of amps I can draw off that cable?"

I had a customer once who insisted on using a small csa of cable to feed a detached garage. After I'd done the cable calcs, the maximum load on that cable was no more than 3A!!!

You need to work out your maximum loading on the cable, then calculate the cable size based on all the applicable factors (of which cable length and volt drop is but one).

 

[ban-all-sheds]

daphantom - this is a good guide to working out what cable you need, as it covers more than just voltage drop, unlike the TLC one:

http://www.kevinboone.com/cableselection_web.html

That said, I don't know if it's been updated to take account of the new voltage drop limits in the latest Wiring Regulations, so you'll have to double check that aspect using the TLC calculator:

http://www.tlc-direct.co.uk/Technical/Charts/VoltageDrop.html

(select 2-core PVC SWA even if you are using 3-core XLPE or it will make invalid assumptions).

As for connecting it up, if you want to come off the house CU you'll need a spare way in a non-RCD section or the RCD will conflict with the one in the garage CU. You'll also have to introduce a metal adaptable box somewhere as you almost certainly won't be able to gland the SWA into your CU.

Splitting the meter tails via Henley blocks and taking the garage supply from a metalclad switchfuse would be better, but unless you have an isolation switch before your CU that would mean pulling the main fuse, which can't be recommended to a DIYer.

Finally for your own safety, and that of other and future occupants, the cable to the garage and the circuits there should be tested before and after energising to confirm that all is well with continuity, insulation resistance, polarity, fault loop values, RCD operating times etc.

 

[daphantom]

daphantom - this is a good guide to working out what cable you need, as it covers more than just voltage drop, unlike the TLC one:

http://www.kevinboone.com/cableselection_web.html

That said, I don't know if it's been updated to take account of the new voltage drop limits in the latest Wiring Regulations, so you'll have to double check that aspect using the TLC calculator:

http://www.tlc-direct.co.uk/Technical/Charts/VoltageDrop.html

(select 2-core PVC SWA even if you are using 3-core XLPE or it will make invalid assumptions).

As for connecting it up, if you want to come off the house CU you'll need a spare way in a non-RCD section or the RCD will conflict with the one in the garage CU. You'll also have to introduce a metal adaptable box somewhere as you almost certainly won't be able to gland the SWA into your CU.

Splitting the meter tails via Henley blocks and taking the garage supply from a metalclad switchfuse would be better, but unless you have an isolation switch before your CU that would mean pulling the main fuse, which can't be recommended to a DIYer.

Finally for your own safety, and that of other and future occupants, the cable to the garage and the circuits there should be tested before and after energising to confirm that all is well with continuity, insulation resistance, polarity, fault loop values, RCD operating times etc.

thanks for that! I can use the meter tails from the separate obsolete shower switchfuse and change the existing fuse box to a metal adaptable box for glanding then get the appropriately rated switchfuse for the new cable? I am actually a time served electrician and did the 16th edition! Been out of the game since 1996 though and my brain has seized up it seems lol