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getting power to workshop

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Ken Lighten12/06/2012 23:04:02
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246 forum posts
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I've got a workshop 30 metres from my house, I want get electricity to it from the consumer unit indoors, I know I need armoured cable and how to lay it but not what size. I should think that there will be a heater, fridge, and normal power tools plus lighting in it - all advise gratefully received - i'm only laying the cable by the way, getting a lecky to connect it properly (eventually!)

Gizwaz12/06/2012 23:15:55
8 forum posts

Are you putting a small consumer unit in there so you can have lighting and power circuits? If so I'd go for 6mm 3c swa ( 3c gives you an extra core to use as an earth in addition to the armouring) , that way you have the capacity for a little more load if required in future. If not, and you're just gonna have a couple of sockets on a radial with the lighting spurred off then 4mm will suffice.
Also do you have an RCD in your fuseboard indoors? as these are invaluable protection and required for protecting any cables that run outside.

hth

Cliff

Ken Lighten12/06/2012 23:28:33
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246 forum posts
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Hi Cliff,

Yeah, I'm going to put a seperate unit in the workshop with seperate breakers for lighting and sockets, there are RCD breakers in the indoor one on the house sockets, I was intending on having another one added for the workshop - I thought 4mm would be the one, but your suggestion for 'future proofing' is a good idea - thanks

Codename-John12/06/2012 23:38:12
1087 forum posts
18 photos

Ken, in England or Wales you`l need a Part P compliance cert for any work carried out exernally and a new circuit connected to your consumer unit, to issue one ALL of the work must be completed by a competant person, i understand you may be trying to save a few quid by doing some of the work yourself, but the very fact you need to ask what size cable should be used proves you are not competant, there are regulations regarding burying cables, or cable support methods if above ground, its not just a case of banging a cable wherever`s easiest, then you have all the calculations to consider such as maximum demand ( power tools, heating and lighting requires more than just a little radial with spurs), cable volt drop, protection size etc

Like with gas and the gas safe scheme, you wouldnt expect to install a boiler and all associated pipework etc yourself then just ask a registered person to "just connect the end" they`d get strung up if there was a problem, electricity is just as dangerous

Mike Etheridge 112/06/2012 23:50:55
1520 forum posts
415 photos

Ken,

Cliff is absolutely right on this issue. I have spent many years in he electrical business on design and would normally carry out a volt drop calculation on the required cable to ensure the voltage did not drop below that recommended in BS 7671-the 17th edition of the IEE regulations. As Cliff suggests because the workshop will be beyond the 'earth bonding zone' of your house an earth leakage trip should be used within your consumer unit. You may have an RCD controlling your general socket outlets in the house but if possible you should introduce a similar device to control the workshop sub-main cable and if there is room within your consumer unit an RCBO should be installed. This is a combined circuit breaker and earth leakage trip. The rating should be 32amp (breaker) and 30 milli-amp (earth leakage trip.) If your circuit breakers are one module wide then an RCBO is usually two modules wide. If you cannot fit an RCBO in then use a 32 amp Circiut breaker and cable link to an RCD (Residual current detector- 30 milli-amp) fitted externally to the consumer unit in its own enclosure.

The idea of using a 3 core cable is also common practice to ensure a good earth so you are not just relying on the cable armouring.---6mm2, 3 core PVC/PVC/SWA/PVC armoured cable seems about right but 4.0mm2 XLPE/LSF thermosetting cable equivalent may be OK ---Calculation needed!

'Part P' should be applied as suggested such that any connections to your consumer unit are made by a competent person with appropriate tests,, but of course that competent person could approve your cable installation method. Cables if  buried are usually ducted at 300mm depth with cable warning tape at 150mm depth or so. Alternatively interlocking cable tiles are used in place of duct. (Polypipe)  

Mike

 

Edited By Mike Etheridge 1 on 12/06/2012 23:53:44

Edited By Mike Etheridge 1 on 13/06/2012 00:03:18

Edited By Mike Etheridge 1 on 13/06/2012 00:05:18

Biggestgerbil12/06/2012 23:54:35
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69 forum posts
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I well see "Codename-John"'s point. And up to a point, he is correct. However, consider that the sockets in your house are all on one circut of "2.5mm2" and then you can run a couple of 1kw heaters and every thing else you have up to 20amps, 4800watts.

I ran 10mm2 t&e to my shower switch, when the landlords inspector saw it he laughed himself silly. Overkill. I think Gizwas has the right idea, no offence to CJ, just make sure everything's waterproof and correctly earthed.

graham kindberg112/06/2012 23:55:08
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129 forum posts

Hi Ken

I am a Sparkie with only 43 years experience, just put my permanent sub main in my workshop.

As i hate any form of volt drop, and tend to run lots of lights and machinery, and an air con planned. I always go for the higher end of the calculations (diversity, contingency, resistivity, etc)

You mention the workshop is 30 metres from the house, you need to measure the cable run from the fuse board, to where the sub board is to be mounted. Take into account the run up and down walls etc. 30 metres is some distance so you will need to accurate.

Without all the info, i would tend to be looking at a minimum of 10mm cable though.

Without looking at any reference, 10mm would be rated about 45 amps, however you would loose about 4 mv/amp/metre through copper losses.

Long after the price is forgotten, the quality remains.

Graham

Codename-John13/06/2012 00:05:05
1087 forum posts
18 photos

Biggest gerbil, there is no upto a point about it, its regulation and if somebody got injured as a result of your uncompetant actions you can go to jail on manslaughter charges !

and a 32amp domestic socket ring consists of 2 x 2.5 mm cables run in parallel or a for a radial 4mm cable, if it was as easy as " make it waterproof and properly earthed" we wouldnt need a few hundred pages of bs7671 and any tom dick or harry could be an electrician

Mike Etheridge 113/06/2012 00:16:40
1520 forum posts
415 photos

Graham,

Showers these days are normally controlled with a 45 amp DP switches and 45 amp circuit breakesr so your 10mm2 T&E cable was absolutely right.

John only one page of BS 7671 is needed for a quick volt drop calc.

Graham,

Nothing wrong with a larger cable if you can terminate it OK and afford the cost. But I have witnessed some cable installations are far greater in size than the incoming electricity boards main cables and sub switch/fuses also larger so there is no discrimination with the electricity authority main fuses.

Thank god I have just retired----this is making me feel ill!

MJE

Biggestgerbil13/06/2012 00:16:49
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69 forum posts
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B****r me, there is some knowledge on this forum.

My workshop is 45mtrs from the nearest socket. I have run 2.5mm2 to that socket and connected with a standard 13amp plug. It terminates in a cooker box, so that I can turn everything off at the same time. I have the usual modellers tools and stuff, couple of 5' lights, pillar drill, sander, scroll saw and battery chargers. I take it that I am offending some sort of regulation? Or the EU?

On second thoughts, I may be the type of person that the electricians mum warned him about when he first qualified.

Sorry

Codename-John13/06/2012 00:21:09
1087 forum posts
18 photos

But more than one page is required for installation of a cable buried in the ground in a special location eh mike wink

Mike Etheridge 113/06/2012 00:30:42
1520 forum posts
415 photos

Biggestgerbill,

Despite my time in the electrical industry the wiring installation in my house and garage is awful.I suspect it was caried out by a former BT engineer. To rewire the place with its solid ground floor would be so disruptive, so apart from add a few sockets and repair obvious bodge ups that are accessible I have done nothing. Part P was introduced so that the bodge-ups could be excluded and the installations safe. Check you have no loose neutrals as these can cause fires and get an approved electrician/ testing company to do a 5 year check to BS 7671. This may be a future/existing requirement for house sales. (Mine would fail)

MJE

Biggestgerbil13/06/2012 00:56:58
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69 forum posts
1 photos

Mike

In all fairness, I have all due respect for skilled tradesman. I really do see the need for gas and electricity regs, both are dangerous. I am (was) an auto electrician and know what havoc can be wreaked by 12v.

I get the feeling that Ken is going to DIY it whatever is said on this thread. We all want him to be safe and not get hurt.

Many years ago, as a favour to a friend, I went to move his fathers piano. It had a heater inside it to keep the temprature constant. He said that he had unplugged the heater and the extension needed pulling out of the piano. So muggins here put his hand into the piano to retrive the extension. Next thing, I am across the room on my head. The extension had a 13amp plug ON BOTH ENDS!!! I was lucky that time. There have been more serious events at the hands if the "amateur sparks"

BG

Edited By Biggestgerbil on 13/06/2012 00:59:30

Mike Etheridge 113/06/2012 07:59:11
1520 forum posts
415 photos

BG,

You were lucky to survive that one!

I used to work with Boy George's uncle (Eddie Williams RIP). He was an electrical inspector/ Clerk of Works. He managed to blow one of his fingers off by working on a bedroom mirror light that was live. He wife called out to him that his dinner was ready and he turned round and touched a live terminal.

I was once asked to inspect an electrical installation that had caused an injury in an industrial building. The injured person was still in the building but it was obvious that he had mishandled the electrical switchgear which was in a poor state.

Auto electricians need magic wands-I assume you still have yours?

I will have a look at BS 7671 this morning and do a manual calculation to check the size of Ken's cable. Of course these days there are software programs to do the same thing. 'Amtec', 'Cymap' etc.

Mike

Edited By Mike Etheridge 1 on 13/06/2012 08:00:33

Ben B13/06/2012 08:48:36
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1399 forum posts
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I'd do it once and do it properly.....

But I do agree that PartP has an unwanted side-effect: people are more likely to leave an inadequate system rather than sort it out. e.g. when I bought my house the entire thing was one ring main and this included a spurred night storage heater! And the lights to the upper floor were in "vulcanised rubber" coated wires in rusty tin tubes. Nasty or what? But because it was done prior to partP it was legal. If I wanted to replace it with seperate ring circuits for the light and sockets and for the different floors (and therefore make it safer) I could be at risk of making it illegal.

The problem with making electrical supplies to out-buildings such a problem is that people are going to be tempted to not bother and just run long extension cables with the trip hazards, over-loading and spade-related problems that they entail.

Doesn't seem to make sense to me!

I'm not suggesting building regs aren't a good idea, just that what they actually do is prevent someone who knows pretty much what they're doing from doing it (with a bit of help here and there) and encourages god awful lash-ups and leaving clearly inadequate systems as they are.

We had a situation where our boiler broke and due to a lack of sockets (in the aforementioned house) my wife decided to run three heaters off an extension cable! Unfortunately the cable was still on the reel and therefore had 10A rating. The three heaters combined was 30A. Luckily it wasn't my best extension reel- the inner 50% of the cable was just molten rubber and fused wires (when the inevitable happened).

Mike Etheridge 113/06/2012 10:42:30
1520 forum posts
415 photos

Ben,

The only limitation on the number of sockets on a ring circuit was/ is covered by floor area served.

Rubber insulated cables were used prior to PVC insulated cables in the 1950's / 60's and most would fail insulation tests these days and would be presented in a report as needing re-wiring. Lighting cables in the past did not include  CPC's (earth wires) which are now required.

Can someone shoot Ken as its his fault all this lot is coming out?

MJE

Edited By Mike Etheridge 1 on 13/06/2012 10:43:05

Edited By Mike Etheridge 1 on 13/06/2012 10:43:33

Ernie13/06/2012 11:00:22
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2511 forum posts
20 photos

Well Guys,

I hate to admit this, and all you leccy types will go faint, but, I have a length of exterior quality cable hung from a sturdy wire. It goes from a socket outlet in the house. It is fixed to a tree half way across, On the workshop end, there is a large fused multipoint, which in turn is fixed to another multipoint, and another, etc. Now before you all throw up your hands in horror, I've used this system for at least 20 years in various houses, without a sniff of a problem.

ernie

Biggestgerbil13/06/2012 11:08:20
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69 forum posts
1 photos

I am in awe of the network/jointer guys working on live cables in a hole in the ground in the pouring rain...

Ben has a good arguement, folks like me who flaunt all regs to get power to the workshop. The farmer, who owns the yard where I have my workshop, had a problem with his supply. It kept tripping his ELCB, but only when he used his 3 phase MIG welder. Sent the welder off to be serviced and, if required, fixed. The MIG folks fitted a new cable and one or two other things and sent the welder back, with a largish bill. Plugged it in and same problem. Then we noticed that the bench grinder lead was smoking when we used the MIG on the (steel) workbench. Unplugging the bench grinder cured all the symptoms. But not, of course, the problem.

Edited By Biggestgerbil on 13/06/2012 11:09:47

Mike Etheridge 113/06/2012 11:10:24
1520 forum posts
415 photos

Ernie,

Make sure your wife depending on your relationship does not hang washing on the cable, and wear rubber soled boots in the workshop and ensure your will is updated.

Send a copy of your installation detail to the NIC and ECA plus the IEE and ask for comments. They are likely to 'send the boys round'!

MJE

Ben B13/06/2012 11:19:07
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1399 forum posts
4 photos
Posted by Mike Etheridge 1 on 13/06/2012 10:42:30:

Ben,

The only limitation on the number of sockets on a ring circuit was/ is covered by floor area served.

Rubber insulated cables were used prior to PVC insulated cables in the 1950's / 60's and most would fail insulation tests these days and would be presented in a report as needing re-wiring. Lighting cables in the past did not include CPC's (earth wires) which are now required.

Can someone shoot Ken as its his fault all this lot is coming out?

MJE

That was kind of my point (not the bit about shooting Ken ). This lady had been living in the house for donkeys years (since the 50s). With an over-loaded ring main and rubbish (and perhaps also dangerous) wiring. It's only deemed a fail when someone tries to buy the house. At that point it's not actually illegal to leave it as it is, but it might be to upgrade it to make it safe(r). It just seems a bit strange. I can see PartP has good intentions but it has the consequences of people leaving things as they are or bodging. Which seems sub-optimal.

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