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Rosco



Member Since: 03 Dec 2010
Location: Burntwood
Posts: 1833

United Kingdom 2015 Defender 110 Puma 2.2 XS CSW Montalcino Red
Power Supply to Garden Workshop
Mrs Rosco is having a garden workshop to do her arty wool dying delivered this weekend, which will then need kitting out, insulating, etc, etc and will need a power supply running too it.


I'm the first to profess at not being all that good at DIY, but should be able to tackle this task fairly well. My question is over the electric supply. I'm yet to figure it all out, but I think I'm right in saying she intends to run 4 (possibly more?) of the twin ring electric hobs, plus lighting, couple of microwaves, ipod, laptop, etc. What information do I need to be looking for on the appliances to calculate how much power she needs? And at what point does trying to run it from an extension cable become ill advised?


Thanks in advance


Rosco Thumbs Up 2007 - Stornoway Grey 90 XS SW - Gone
2002 - Black Discovery II - Gone
2014 - Montalcino Red 110 XS SW
Post #726322 30th Aug 2018 6:46pm
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Bluest



Member Since: 23 Apr 2016
Location: Lancashire
Posts: 4208

United Kingdom 2007 Defender 110 Puma 2.4 XS CSW Java Black
Each appliance should have an input power in Watts marked on it. Yiy can just add everything up and speak to Electrician about what's needed. Will she be using all those things at once? That's potentially quite a hefty power supply for shed. 2007 110 TDCi Station Wagon XS
Post #726324 30th Aug 2018 6:56pm
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barbel jim



Member Since: 12 Dec 2012
Location: Northants
Posts: 1423

United Kingdom 2005 Defender 90 Td5 HT Tonga Green
I would say straight away Confused
You need a proper designated armored supply wired back to you consumer unit, fitted and certified by a qualified competent person. Its just not worth bodging it a s your house insurers will have a field day
Post #726327 30th Aug 2018 6:58pm
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custom90



Member Since: 21 Jan 2010
Location: South West, England.
Posts: 20342

United Kingdom 
An extension cord is also really only a temporary fitting and max load 13A.

I'd echo what Jim said above, but unfortunately comes at a cost! $W33T $0U7H3RN $UG4R
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Post #726330 30th Aug 2018 7:01pm
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AndyT66



Member Since: 19 Sep 2016
Location: Bedford
Posts: 148

England 2004 Defender 90 2.5 TD XS CSW Zambezi Silver
Hello Rocco, as Jim says ideally you should run a new cable from your main consumer unit to something like this https://www.screwfix.com/p/british-general...unit/1926g mounted in your workshop. You can then have separate lighting and appliance circuits from this unit.. The new supply cable would need a part p qualified electrician to fit it. Cheers Andy
Post #726341 30th Aug 2018 7:38pm
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leeds



Member Since: 28 Dec 2009
Location: West Yorkshire
Posts: 8580

United Kingdom 
Rosco, simple advice is get a qualified electrician in to do the work as that amount of work needs certifying to part 17 or even part 18 Regulations these days.

As pointed out an extension lead is 13 amp or 3 kW

Now 3 kW is say an electric kettle.

8 electric hob rings at say 1 kW each or 8 kW in total will fry your extension cable.

If possible get steel sheathed cable underground at correct rating.

Overhead used to be possible on a properly tensioned gantry wire. Not sure if still allowed.

So get a proper qualified sparky in and work out current max total load and then allowed another 50% for those extra toys your wife will need.

Brendan
Post #726342 30th Aug 2018 7:42pm
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Rosco



Member Since: 03 Dec 2010
Location: Burntwood
Posts: 1833

United Kingdom 2015 Defender 110 Puma 2.2 XS CSW Montalcino Red
Thanks for the quick respknses all and confirms my suspicions.

I know the current mains board is dated, so I can see this little venture getting expensive Rolling Eyes 2007 - Stornoway Grey 90 XS SW - Gone
2002 - Black Discovery II - Gone
2014 - Montalcino Red 110 XS SW
Post #726345 30th Aug 2018 7:48pm
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leeds



Member Since: 28 Dec 2009
Location: West Yorkshire
Posts: 8580

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Better expensive and safe rather then cheap and new shed/house burning down due to an electrical fault!


Brendan
Post #726348 30th Aug 2018 7:57pm
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barbel jim



Member Since: 12 Dec 2012
Location: Northants
Posts: 1423

United Kingdom 2005 Defender 90 Td5 HT Tonga Green
Not necessarily........

The outdoor cable will have to be protected itself, so tacking onto an old consumer unit might not be such an issue.
My workshop was less than £400 , 50 meter run of 16mm armored socket ring main and lighting. I did all the work and sparky tested and certified Thumbs Up
Post #726349 30th Aug 2018 8:03pm
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Rashers



Member Since: 21 Jun 2015
Location: Norfolk
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United Kingdom 2014 Defender 110 Puma 2.2 USW Corris Grey
Good advice from Brendan. Thumbs Up

For information and interest to all (this isn't suppose to be instructions on how to do it), if your main supply (electricity board supply to use a better phrase) is what is known as a TN-C-S or PME supply (the main electricity supply fuse will usually have a label, but not always) you don't want to be exporting your earth from the house to an external building unless you know what you are doing. Another way of discovering whether your supply is PME, an earth wire will be connected from the neutral terminal of the main fuse block to the consumers main earth terminal. Most (but not all) properties these days have this kind of electricity supply.

Two options. 1. Send a supply cable out to the shed with an earth cable the same size or larger than the main bonding conductor in the house (this is what as known as extending the equipotential bonded zone and it will usually require installing a 16mm2 or 25mm2 earth cable) 2. Isolate the earth as it enters the external building, protect the cable at the source with an RCD (Earth Leakage Circuit Breaker) and provide a point of earth adjacent to the external building using an earth electrode(s).

It's not quite a simple as the above, and you need to be making sure the earth electrode has a low enough resistance and the RCD is the correct mA rating. Oh, and the cable if buried should be armoured with steel and ideally buried in a bit of ducting and not a hose pipe, please Banging Head

Yes, there are hundreds if not thousands of external buildings out and about that do not have any of the above done, but that's what should be happening. And just because it works, sadly does not mean it is safe.

Doing the above is not cheap I'm afraid. Again, as Brendan says, talk to a good electrician.
Post #726353 30th Aug 2018 8:24pm
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Bluest



Member Since: 23 Apr 2016
Location: Lancashire
Posts: 4208

United Kingdom 2007 Defender 110 Puma 2.4 XS CSW Java Black
I had a new consumer unit for my garage, two seperate circuits for sockets and one for lights. It wasn’t that expensive, maybe a few hundred. I saved a bit of money by running the cables and conduit, mounting the sockets etc myself once the sparky had specified it. He did all the actual connections and signed it off. 2007 110 TDCi Station Wagon XS
Post #726356 30th Aug 2018 8:31pm
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Caterham



Member Since: 06 Nov 2008
Location: Birmingham
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England 2011 Defender 110 Puma 2.4 XS CSW Stornoway Grey
in this crazy world there's not point employing a fantastic electrician who may have recently finished re-wiring the Shard in London....he needs to be part P certified ie for domestic installations. commercial electricians don't need to be part P Confused

your best option is likely the RCD route. you'll likely find that'll be the only option in all honesty and 30mA at that.

I might be right in saying no one has been killed with an electrical supply protected by an operational 30mA RCD.

at a guess from what you've said you're possibly looking at a 10kW supply which if you know anything about electric showers and the cables associated with them you're gonna be looking at a fairly hefty supply cable (by domestic standards). without looking at any books and assuming you'll be looking about a 50 mtr run of cable I'm going to guess you'll be looking about a 16 -25 mm cable (armoured as mentioned above) to ensure correct / minimal volt drop. Also look at a 3 core cable which will hopefully avoid the need for a separate earth / CPC as noted above.

Thumbs Up good luck.
Post #726364 30th Aug 2018 8:53pm
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v8bob



Member Since: 14 Mar 2018
Location: Midlands
Posts: 317

United Kingdom 1998 Defender 90 300 Tdi HT Nato Green
Well how much is this really going to be used?
How about using a petrol generator?
As a quick fix to get things up and running this could be an option.
Bob
Post #726367 30th Aug 2018 9:08pm
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miker



Member Since: 13 Sep 2015
Location: Surrey
Posts: 1763

United Kingdom 1999 Defender 110 Td5 CSW Rioja Red
Gas hobs and a couple of calor bottles would be the way I'd look. Runnin upwards of 8kw into a she's becomes a pain!
Post #726369 30th Aug 2018 9:16pm
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apt100



Member Since: 05 Mar 2015
Location: Derbyshire
Posts: 1547

United Kingdom 2016 Defender 90 Puma 2.2 XS CSW Aintree Green
Rashers wrote:
Good advice from Brendan. Thumbs Up

For information and interest to all (this isn't suppose to be instructions on how to do it), if your main supply (electricity board supply to use a better phrase) is what is known as a TN-C-S or PME supply (the main electricity supply fuse will usually have a label, but not always) you don't want to be exporting your earth from the house to an external building unless you know what you are doing. Another way of discovering whether your supply is PME, an earth wire will be connected from the neutral terminal of the main fuse block to the consumers main earth terminal. Most (but not all) properties these days have this kind of electricity supply.

Two options. 1. Send a supply cable out to the shed with an earth cable the same size or larger than the main bonding conductor in the house (this is what as known as extending the equipotential bonded zone and it will usually require installing a 16mm2 or 25mm2 earth cable) 2. Isolate the earth as it enters the external building, protect the cable at the source with an RCD (Earth Leakage Circuit Breaker) and provide a point of earth adjacent to the external building using an earth electrode(s).

It's not quite a simple as the above, and you need to be making sure the earth electrode has a low enough resistance and the RCD is the correct mA rating. Oh, and the cable if buried should be armoured with steel and ideally buried in a bit of ducting and not a hose pipe, please Banging Head

Yes, there are hundreds if not thousands of external buildings out and about that do not have any of the above done, but that's what should be happening. And just because it works, sadly does not mean it is safe.

Doing the above is not cheap I'm afraid. Again, as Brendan says, talk to a good electrician.


I was going to mention not exporting PME, but you have summarised it well already Thumbs Up

Just to add about 30mA RCD...
Many people call the green/yellow wire "earth", but there is usually a voltage difference between it and true earth. Inside a building it doesn't usually matter. When you take it outside it can be dangerous. If you have a PME supply, and there is a broken neutral in the supply network, then the green/yellow wire (and anything metal connected to it) can be close to the full 230V supply voltage above true ground. And an RCD won't be any help at all.
Hence it is illegal to have PME supply at eg caravan parks and marinas. And usually not recommended for supplies to outdoor buildings.
Post #726381 30th Aug 2018 11:02pm
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