bonzoronnie
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| posted on 2/1/11 at 03:01 PM |
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Any Domestic electricians in the house ?
One of my new year resolutions is to rewire my workshop
Just wondering if any electrical contractors could offer any advice on the correct size of armoured cable to use ?
I know that this is a bit like asking, how long is a piece of string without knowing my current requirements so here's a brief list of the worst
offenders 
180 amp Mig welder & 200 amp ac/dc tig welder ( Never used at the same time )
Air compressor ( 2hp ) Only used part time but there are times when it is used at the same time as one of the welders.
Harrison lathe fitted with a 1hp motor
Small air compressor fitted with a 1hp motor
6 X 5ft strip lights + 4 X 150w halogen spotlights ( Used part time to supplement the strips )
+ The usual crop of hand tools .... Drills, grinders, bandsaw & the likes.
I have no idea of the power rating of my exhisting feed but I do now that it is not up to spec & it's currenty connected to my consumer
units cooker fuse 
Had a rollocking recently ( Quite rightly so ) from an engineer inspecting my household electrics .... Feed to workshop under rated & connected
to somewhere where it shouldnt be 
I have some spare places in my consumer unit so it shouldn't be too difficult to fit a dedicated fuse .... Not sure of the correct size to use
though
Should I fit the armoured cable directly into my consumer unit & out to a new consumer unit in the workshop ( I suspect not ) !!??
Or do I take a tail of HD cooker/shower cable to an isolation box near the consumer unit before fitting the armoured cable & runnig it out to the
workshop ( I suspect so ) !!??
It may help to say, the length of cable required is about 7 metres.
Any advice would be most welcome 
[Edited on 2/1/11 by bonzoronnie]
[Edited on 2/1/11 by bonzoronnie]
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RAYLEE29
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| posted on 2/1/11 at 03:19 PM |
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hi, you can run armoured from the garage to a junction box in the house, then feed this from the main distribution board you can get a standalone rcd
box to do this with personally i use a 30amp breaker in the fuse box and run a sparate board in the garage from it i have simillar needs to yours and
have never tripped the breaker yet in the house yet .
the breaker is there to protect the wire.
Ray
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franky
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| posted on 2/1/11 at 04:42 PM |
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As above, thats what I do too, its the proper way of doing it and easy too.
Oh, that sounds like a nice workshop too
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MikeR
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| posted on 2/1/11 at 05:25 PM |
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Obviously when you've done this you'll get a spark to connect it to the main supply and certify it, you're just asking to save
yourself from making expensive mistakes
(thats covered the legal bit for you).
How are you going to wire up the garage? Cables nailed (via the little clips) to the wall or inside trunking? lots of single sockets or doubles?
(i'm curious for when i get mine done as to the best approach)
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bartonp
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| posted on 2/1/11 at 05:42 PM |
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See here for cable size calculator & other stuff (I use them & recommend them too...):
http://www.tlc-direct.co.uk/Technical/Charts/VoltageDrop.html
If a considerable distance to the garage then size for min allowed volt drop, this will be over rated for the current you need.
Phil.
Edit to say I have Henley blocks T-ing off my house meter tails (after meter before house CU)into a fused isolator thence to 25mm2 SWA off many
(30?)meters to the garage where it meets a small consumer unit.
[Edited on 2/1/11 by bartonp]
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bonzoronnie
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| posted on 2/1/11 at 05:57 PM |
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Thanks for the advice so far chaps
The workshop would be nice if I could keep it tidy
MikeR
When I first wired up the workshop/garage, I just used electrical stuff that I had on tap.
Old style fuse box ( Ceramic fuses ), cables held in place with cable clips & standard domestic plug sockets/light switches
Hoping to get the new roof fitted this spring & have decided to try & do a pucker job on the electrics this time
New consumer unit, propper commercial sockets & switches , cables in conduit etc.
Thinking perhaps one lighting ring for the striplights, another for my halogen spotlights
Ringmain for the plug sockets
Sepperate feeds to the welder, large compressor & lathe
I am quite lucky, my neighbours son is a sparky ( went to school with him ), he'll be quite happy to inspect & sign it all of for me for a
few beer tokens 
Here's the rub .... he'll probably will not visit his mum untill Easter so I can't ask for his advice & the current wiring regs
& I really want to make a start on things.
Dead right though .... Definately don't want to be making any expensive mistakes, much prefer to do the job right, the first time
[Edited on 2/1/11 by bonzoronnie]
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jrrsparky
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| posted on 2/1/11 at 06:32 PM |
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You dont say what type of consumer unit you have in the house, is it RCD protected ? if so you can just fit the appropiate MCB, if not you will need a
seperate RCD and metal enclosure to terminate your swa into.
As regards the cable size 1HP is = to about 3 amps, and the welders should have a lable showing the max current drawn, as these seem to vary quite a
lot from make to make.
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bonzoronnie
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| posted on 2/1/11 at 06:47 PM |
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quote:
Originally posted by jrrsparky
You dont say what type of consumer unit you have in the house, is it RCD protected ? if so you can just fit the appropiate MCB, if not you will need a
seperate RCD and metal enclosure to terminate your swa into.
As regards the cable size 1HP is = to about 3 amps, and the welders should have a lable showing the max current drawn, as these seem to vary quite a
lot from make to make.
Yes I should have mentioned, I have a modern consumer unit fitted & is RCD protected.
The whole house was professionally re wired a few years ago.
I guess I should check the current rating on the welders data plates, both were fitted with a round Blue 3 pin plug 15/16 amp if memory serves me
right ?
Thanks for that information it is much appreciated
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jrrsparky
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| posted on 2/1/11 at 08:00 PM |
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I would recomend 6mm 3 core SWA, Current Capacity 56 amp, and a 45 amp or 50 amp mcb. I suggest 3 core so you can use a core for the earth and
terminate the swa straight into the ( plastic ? ) consumer unit.
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bonzoronnie
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| posted on 2/1/11 at 08:17 PM |
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quote:
Originally posted by jrrsparky
I would recomend 6mm 3 core SWA, Current Capacity 56 amp, and a 45 amp or 50 amp mcb. I suggest 3 core so you can use a core for the earth and
terminate the swa straight into the ( plastic ? ) consumer unit.
Thank you for that
On the subject of Earthing, would it be prudent to place an earth spike in the ground for the workshops new consumer unit or is the exhisting domestic
on sufficient ?
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JoelP
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| posted on 2/1/11 at 08:47 PM |
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sparks will argue all day whether it counts as 'exporting the earth' if you use the house earth in a seperate outbuilding. The consensus
as ive understood it is to use the earth at the house to connect the swa armour to, and an earth rod at the garage end for the new mini consumer unit.
You can link them anyway if you want.
I'd be very suprised if you needed more than 32A in the garage; but i suppose that the number of people working at once is more telling than the
equiptment that you have fitted.
6mm swa is the way forward, or 6mm t&e in conduit if you want to save money.
Beware! Bourettes is binfectious.
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bonzoronnie
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| posted on 2/1/11 at 09:10 PM |
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Cheers for that JoelP
Just Billy no mates me, working alone in the workshop
I guess absolute max .... One of the welders being used, 800w of lighting & the 2hp compessor possibly cutting in now & again when being
used.
The domestic supply is right next to my back door ( Internal ), the suspended cable entry into the workshop is about 6 metres from the back door,
quite a short run really.
Thanks for all of the help chaps
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daniel mason
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| posted on 2/1/11 at 09:34 PM |
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I get worried stiff reading these threads. A 6mm t+e has a 2.5 mm cpc. You will need a 10mm cpc to the garage. A 6mm armoured plus the armourings (if
glanded correctly with the banjo will equate to 10mm. But I would strongly advise you not to wire the garage yourself. Your better off Saving your
life than a fee quid in my opinion. If you decide to wire it yourself u2u me and I will talk you through it
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