Garage Electrics

[podge]

New to this forum so be gentle with me please
Im coming to the end of a self build garage and its time for the electrics
Now I want to point out that I'am NOT an electricitian and not trying to pretend that I'am All the work is been done by a mate whose fully quallified But he's just got married and is spending next 6 weeks touring America But before he went he left me a list of things to do and things to get and yes I've lost the list Idont think he'll be to happy if I rang him this is where I need your help. The garage is situated 20metre's from the house an armour cable is been put along the drive (which will be block paved) the garage will have 6 double sockets 6 flourecent lights 2 on one switch 2 on another switch and the other 2 with there own switches there will be 2 heavier sockets for a 3hp commpressor
180amp mig welder 200amp arc welder (I have some classic cars to restore) Out side there will be a security light and a floodlight
I think he said something about a single CU for in the house
what size?
What size armour cable will I need to get ?will 2.5 t&e be ok for sockets ?1.5 t&e for lights ?
What size for the heavier socket? would this need to go in a ring?
All the cable will be in condiut
Am I allowed to do first fix? thought I was but after reading a few posts not sure now
The garage is under 30sqm so not under building regs incase you were wondering
I know its a lot to ask but it will get me out of a embarassing situation
CHEERS

+++++++++++++++++++++++++++++

Forgot to add that there will be a CU going in the garage and an earthing rod inside garage as well
______________________________

Lynda, moderator

please note forum rules, general information, item g

 

[Adam_151]

We could spec it up for you, but we'd need a design and as your sparky is going to be signing to say he did it, he might not be happy signing for design of an install he didn't design!

 

[davy_owen_88]

I think he'd rather do it since he's signing it off but here goes:

I think he said something about a single CU for in the house
what size?

Do you mean a new CU that will cater for everything in the house including the new feed to the garage? If so count how many ways you currently have and then add 1. Or do you mean a small additional CU just for the garage feed? If so 3 ways is fine.

What size armour cable will I need to get ?will 2.5 t&e be ok for sockets ?1.5 t&e for lights ? What size for the heavier socket? would this need to go in a ring?

1x 32A ring main
1x 6A lighting circuit
2x 16A supplies
Max demand: 70A - 16mm² SWA.

2.5mm² t&e for ring circuit and also for the 2x individual radials for the 16A sockets.
1.5mm² t&e for lighting circuit.

Am I allowed to do first fix? thought I was but after reading a few posts not sure now

Yes you can.

 

[breezer]

are you sure he never said dig a trench to put the armoured cable in?

you cant really first fix as it will be in conduit (unless you can bend metal conduit (plastic will be of no use)

since you are using conduit you dont use wire armoured to feed the sockets, you use singles which go in the conduit

 

[podge]

Thanks for quick replys the CU for the house is for the garage supply only
Yes the armour cable is being buried the drive is currently concrete this is being dug up and will be eventualy replaced withblock paving.the condiut is for inside the garage

 

[securespark]

1x 32A ring main
1x 6A lighting circuit
2x 16A supplies
Max demand: 70A - 16mm² SWA.

No diversity allowance? That only leaves 30A for the house!

 

[davy_owen_88]

If you are using conduit throughout the entire garage you don't want to use twin and earth. Use singles instead as breezer suggested.

This is ideal for your situation - don't forget one of these.

Diversity... 44.8A for sockets + 4A for lights = about 50A so you could drop down to 10mm² SWA.

 

[bernardgreen]

Diversity... 44.8A for sockets + 4A for lights = about 50A so you could drop down to 10mm² SWA.

The OP mentions

2 heavier sockets for a 3hp commpressor

The start up current of this may require a lower resistance in the feed to the garage to ensure reliable starting.

 

[davy_owen_88]

there will be 2 heavier sockets for a 3hp commpressor 180amp mig welder 200amp arc welder (I have some classic cars to restore)

That's 3 things so do you want 3x 16A sockets?

1x 32A ring main
1x 6A lighting circuit
2x 16A supplies
Max demand: 70A - 16mm² SWA.

No diversity allowance? That only leaves 30A for the house!

Diversity... 44.8A for sockets + 4A for lights = about 50A so you could drop down to 10mm² SWA.

The OP mentions

2 heavier sockets for a 3hp commpressor

The start up current of this may require a lower resistance in the feed to the garage to ensure reliable starting.

Nice one secure, look what you made me do

 

[Adam_151]

Not sure plastic would be of no use? its pretty impact resistant from what I can tell with a hammer

Anyway, would any bends actually be necessary?, stick some metal trunking around at ceiling level, DB just below it connected with couplers and bushes, drop to sockets etc in conduit on distance saddles? (of course you still need to be able to thread metal conduit, but at least the stock and die isn't going to break the bank)

Of the top of my head, gut feelings without checking the calcs yet, 2 core 16mm² SWA (like everyone else has said) into a switch fuse with 60A BS1361 at house end, 300ma time delay RCD in tails before it (it sounds like your system is TN-C-S and your sparky has already assessed that it'd be a good idea to TT at the workshop), into plastic 63A rotary isolator at garage end, end the armour there, bring electrode earth into enclosure, and thats the earth that lives with with the live conductors to the DB, which is a hager metal split load CU with 30ma RCD, about 6+4 split is the nearest they do I think, everything but the lights on the 30ma RCD (you really don't want a fault on anything knocking out the lights in a workshop when you might have rotating tools spinning down, might be a good idea for some EM lights as well)

 

[JohnD]

You can get a flexible-ish metal conduit, works out quite expensive, rather like a "metal" flexible shower hose with the metal in a sort of coil and a thick plastic coating over it.

I imagine it would stand up to the typical spade contact. Bury it deep with plenty of marker tape.

I once dug up an armoured Supply cable, thinking it was a tree root, after I'd failed to chop it through with my spade. Had to sit down for a moment when I realised what it was.