# Workshop electricity supply



## Anonymous (14 Nov 2007)

Hi all,

Quick question I hope. I have just moved into a house with a workshop which I have just started buying tools for (morticer and table saw so far). The current shop is running a single socket off the downstairs ring main which I think is not ideal. Therefore I was planning on running a new ring main solely for the workshop using 2.5mm cable. However people seem to be saying on here that I need 10mm !? That sounds massive 

So what is correct ?

thanks


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## OLD (14 Nov 2007)

It is massive but its sized to handle the current for start up of big machines while running other machines at the same time also as labour is expensive you do not want to do it twice . My shop runs on 5sq.mm with table saw, dust extractor, p/t , cross cut saws, etc because there is a max of two running at one time.
The heavy cable feeds a dist.box that supplys ring or radial ,lights,16a dedicated .Volt drop can also be a problem for long runs of the feed cable.


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## p111dom (14 Nov 2007)

Sounds like tosh to me. A 2.5 mm ring main on a 32amp breaker should be fine for anything. Unless you have one of the large(and by large I mean 5hp) woodford unisaw clones which actually require a 32amp supply you should be fine. Bare in mind that it's rare to have more than one machine and your extractor running at any one time. Unless you have a washing machine, drier, freezer and kettle on while you're running your saw and extractor on the same ring I can't possibly see a problem. The limiting factor really is the 13amp fused plug. Many people have just cut into the 32 amp ring in the shop to add a 16amp socket for the machines which require it. I would advise against it as it leaves a machine requiring 16amp protection on a 32amp wire with no additional fuse in between. although there's bound to ba a qualified sparky that will say it's fine.

For larger machines which require a 16 amp supply I personally have run a dedicated wire from a 16amp breaker to the machine via an isolator switch. I have 'hard wired' these machines in as there is a debate about the legality of the 16amp plugs in a domestic application. Some sparky's say they're fine. Others insist that they fall foul of some requirement to adequately shield the terminals of the socket which the 16ampers don't meet. It really is a mine field. I understand the comment about labour being expensive but so is buying thicker cable you don't really need (IMO of course). 

The only thing I have to consider is whether to daisy chain my 16amp supply to a larger planer thicknesser (when I get it ) or run a separate 16 amp supply. It currently only runs to my sanding machine and I can't think of a scenario where I'd be running them at the same time.


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## Maia28 (14 Nov 2007)

Hi Paul,

This is a subject I have been contemplating for a while as my workshop nears completion. Mine is 150' from the house and fortunately already has an armoured cable buried under a concrete path. I did discover that it is run off the cooker switch and on a 40A breaker. I will make a seperate connection to the house distribution box when I have finished, but for the time being it is convenient to be able to switch it off from inside. In general it is not a good idea to have your power from a household ring main and there are regulations governing this. In fact, an outdoor supply should be cnnected via its own RSD. Now for my two penneth worth...

I have installed a seperate distribution box in the workshop with three breakers (32A, 16A & 6A) which cost £30 and a seperate earth rod. I will put in a ring main for general power off the 32A circuit and connect a couple of machines directly to the 16A circuit and lighting off the 6A. This is over cautious, but if you where running off the house ring main and your wife has the hoover on (1200W) you have a heater going (3000W) a dust extractir (1000W) lathe (750W) and someone puts the kettle on you could easily trip the circuit. Unlikely to be any danger, but it would be a hassle on a night like tonight! There are very few incidences of electricution or fires from DIY wiring and the current regs are a bit of a sledge hammer to crack a non existant nut.

How far is your workshop from the house and do you have RSDs? If it where close enough, you could realistically, and within the regs, run a couple of 2.5mm cables overhead as a new ring main directly from your household distribution box.

Andy


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## p111dom (14 Nov 2007)

Maia28":tuf8kio7 said:


> There are very few incidences of electricution or fires from DIY wiring and the current regs are a bit of a sledge hammer to crack a non existant nut.



This is very ture. The whole thing is a huge cash cow for the building / sparky industry. According to the governments own figures the total number of deaths attributable to individuals carrying out DIY electrics in England in 2006 was .........wait for it..........4. Literally more people died in the same year doing truly stupid things like like dropping hairdryers in to the water while in the bath. The irony is that it may have been the extra cost incurred by the part P which prevented them from upgrading their own fuse boxes to MCB's which may have saved their lives. (although if you're stupid enough to use a hair dryer in the bath then you're probably arn't savy enough to do competent DIY!). Distance does play a part and I forgot about a heater (probably because I don't have one). Just make sure you get a few quotes. Screwfix's website is great for checking out if a quote is reasonable or not. Go on their forum page and just say what you want. See if there's any difference of opinion and ask for ball park quotes. The guys on there post as much as we do so they won't want any negative feedback. You could even source someone locally from the site to do the job and at least have a way of telling the rest of the world that he's rubbish if they do a poor job. That's a lot more comeback than you usually get! :wink:


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## Woody Alan (15 Nov 2007)

As OLD says he has a 5mm feed to his shop which is the equivalent of a 2.5mm ring main give or take the design characteristics of how it's laid e.g. within conduit in insulation double or single insulated etc, and is the way to go. http://www.tlc-direct.co.uk/Book/4.3.9.htm
Should help for cable sizes, given the cost vs effort I would put in a 10mm cable but at least a 6mm. 

Cheers Alan


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## Woody Alan (15 Nov 2007)

I would also say don't go playing with what you don't fully understand. for example putting in seperate earth rods etc if you don't have the earth impedance tested you have no idea whether it's adequte and it may not even be neccessary even though it's what the regs imply, if your supply is earth sheathed then it's OK to bring that earth through. I wish Davy Owen still hung around here he would have the definitive answer.

Alan


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## Woodmagnet (15 Nov 2007)

Paul, i hope this is'nt breaking any rules, but i advise you try 
the ultimate handyman forum at www.ultimatehandyman.co.uk
there are experts who will be able to advise you. :wink:


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## gav (15 Nov 2007)

Hi all,

I'm in the process of a workshop build and am at the groundworks stage and hit the same question of what cable I needed to use to supply the workshop. I went to one of our leccies at work so he had no vested interest in it. 

It seems from his explanation that I think I understand you need to consider current draw, length of cable and permissible volatge drops.

In my example I have a distance of 45 metres from the consumer unit to the workshop (man that was some digging to get it 18inches deep all that way to meet the regs). My worst current load is large table saw, dust extractor, dust filter unit, lighting circuits and heater. I think he erred on the cautious side in terms of efficeinceies of motors but the potential total draw was about 30A

For 10mm2 cable the rating is 4.4mv/A/m with a maximum permittable drop of 9.2V. Therefore on this run it is 0.0044X30X45 = 5.94V If I went down to 6mm2 cable the drop was borderline. 

I therefore went for the extra cost of 10mm on the basis of do it once and do it with some headroom after all my daughter like woodworking to and we work together sometimes so more kit might be in use.

He also did a calculation of the impedance to make sure the MCB serving it would work but I'm not sure I understand that one fully to explain it.

Anyway hope it helps

Gav


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## Woody Alan (15 Nov 2007)

> In my example I have a distance of 45 metres from the consumer unit to the workshop (man that was some digging to get it 18inches deep all that way to meet the regs). My worst current load is large table saw, dust extractor, dust filter unit, lighting circuits and heater. I think he erred on the cautious side in terms of efficeinceies of motors but the potential total draw was about 30A
> 
> For 10mm2 cable the rating is 4.4mv/A/m with a maximum permittable drop of 9.2V. Therefore on this run it is 0.0044X30X45 = 5.94V If I went down to 6mm2 cable the drop was borderline.


Good move to go for the 10mm, one of the things to watch out for (although on the face of it something might appear to fit in within spec) is the volt drop because induction motors can behave oddly. On startup for instance they can draw a huge amount of current which means that the volt drop can be excessive which means the motor struggles to get up to speed and so compounds the problem. Tony the MOD knows far more about this aspect of power ratings and loadings than most here it's his field hopefully he can explain this better than I can. My workshop is 30m away and I had a temporary 2.5mm until I laid the 10mm and the difference in the motors performance was very noticable.

Alan


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## Deejay (15 Nov 2007)

Hello Paul

Have a look at 

http://www.tlc-direct.co.uk/Technical/C ... eDrop.html

Cheers


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## White House Workshop (15 Nov 2007)

I've not managed to figure out the wiring to my workshop. I do know it's on it's own breaker but the circuit also covers the garden sheds (attached to the workshop) and one of our outside lamp-posts (we live in a very dark corner!). I have discovered a buried armoured cable going from the workshop to the light, but haven't found the power to the workshop, which I think comes in via the sheds. Pity the poor person who wants a Part P on it someday!

As it is, the 20A breaker hardly ever trips and I have all my 110V machinery protected with an elcb anyway. That's never tripped, although I do test it from time to time and it is working...


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## tenpin (15 Nov 2007)

Hi Paul

i had this same question with my sparky last weekend as i am still tinkering with my workshop....(moving this here, that there...etc) i didn't want to commit to socket positions etc till i knew exactly what i had/wanted.

small Rexon table saw....1.4kw
bandsaw....500w
dust extraction...800w
triton router......2.4kw
lighting....?

where the basics i gave my electrician.....

6mm MINIMUM.....he really wants me to use 10mm armoured for the ability at a later stage if i want to run outside lights....etc

i would stick 10mm SWA in now and save hassle/exspense in the future.

Nick


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## Charley (15 Nov 2007)

Dave's link: http://www.tlc-direct.co.uk/Technical/C ... eDrop.html


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## White House Workshop (16 Nov 2007)

Just one question - how many people run ALL their machinery at once? Can you be operating a router while the table saw is running and pushing something through the bandsaw while simultaneously drilling holes on your pillar drill? I doubt it, unless you're a multi-person workshop. 

In my workshop I run the lights and the dust extractor continuously - that's about 150W for the lights (lots of high efficiency bulbs) and 200W for the extract motor. Beyond that I sometimes have the battery charger plugged in - negligible consumption - and I can only use one major piece of machinery at a time. The most power hungry machine in my workshop is my table saw - 1.5KW, so generally my workshop is using less than 2KW at any one time, and most of the time much less. OK, so there's surges to consider, but those miniscule surges don't heat cable, not in a personal workshop anyway, and even if I allow 100% for surges and then some extra I still only need 2.5mm T&E cable - and it's actually got 5mm.

If I compare that to our sauna which draws 6KW off a sub-box connected to the house ring main it's nothing, especially as the 6KW is continuous during the heating cycle. I wouldn't put a 10mm armoured cable in for any personal workshop anywhere! It would be major overkill - and wasteful of my precious cash.


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## dedee (16 Nov 2007)

I've got an electrician coming soon to install a second fuse box in my garage and run a cable out to the barn ready for the workshop conversion. He's quoted for 10mm but I've no idea what the regs are here :shock: 

Something you should not forget when calculating consummation is your heat source in the winter, unless you have central heating or a wood burner of course.

Andy


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## White House Workshop (16 Nov 2007)

dedee":1ay03uom said:


> Something you should not forget when calculating consummation is your heat source in the winter, unless you have central heating or a wood burner of course.
> 
> Andy


There's always solar gain... I'm lucky - my shop faces due south. Mornings are cold, of course, but by afternoon it's usually warm enough out there. In summer I have to open all doors and windows to stop it getting too hot! The real problem I have in winter is the cold cast iron table on my tablesaw - no heater is going to solve that problem, so I put up with it. Fingerless gloves do a good job


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## Woody Alan (16 Nov 2007)

Freudian slip?


> Something you should not forget when calculating consummation is your heat source in the winter


Surely it's going to be underneath or on top  

Alan


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## Streepips (17 Nov 2007)

Just wired up my workshop, 10mm armoured on a 50 metre run, to consumer unit ( Steel in case it gets clouted ) ran a 16 Amp supply in 4mm to the table saw, another 16 Amp in 4mm to the planer/thicknesser, both supplies exclusive to those machines, plus 2 x 32 Amp ring circuits in 2.5mm for power points ( All using metalclad double boxes and in conduit, and a 15 amp lighting circuit through 1.5mm on the other side of the split BUS bar so that lighting circuit can be on even if all the power side trips or is switched off for maintenance etc.
And I often have the 2HP extractor, the tablesaw AND the thicknesser running at the same time, rip through the saw and feed through the thicknesser. work flow. Whilst of course having the lights radio and other incidentals such as radio, battery charger on as well.


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## White House Workshop (18 Nov 2007)

I trust you'll be getting a Part P certificate for all that wiring as it's 'outside'? :?


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## Anonymous (18 Nov 2007)

thanks for all the replies and advice. For info my workshop is built onto the side of my house as an extension and is about 10 metres from the fusebox. 

Looks like best course of action is 10mm cable 'just in case'. I'll be getting an electrician in to connect it up but plan to run the cable myself (so should only be an hours labour cost so he can check everything).

thanks again


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## Digit (19 Nov 2007)

> Others insist that they fall foul of some requirement to adequately shield the terminals of the socket which the 16ampers don't meet.



Another mine field I promise you. Some years back I returned to my retail unit to find that I had had a visit from the Gestapo, (disguised as Trading Standards Officers) who had cut the 13 amp plugs from a number of items for sale.
Their reason? There were no shields around the base of the three pins so they claimed that people could get a shock from the partially exposed, still live pins.
I pointed out that the plugs were stamped with the appropiate BS number and asked if they were telling me that they did not if fact comply with that BS number.
'We'll put you through to our legal department', they hastily explained, who I asked the same question of.
'They are not safe!' They insisted.
'So they don't confirm to the BS spec?'
'We didn't say that!'
'Yes or no?' I insisted.
'Well, yes. But they are not safe!'
'Shouldn't you be taking this up with the manufacturures then, or is it easier to start on the little boys?' I wanted to know.
'That's not fair!'
'So you are taking it up with the manufacturers?'
Line goes dead, plugs go back on!


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