Garden Workshop Electrics

[Skavenger]

I have built a small workshop lean to up against my existing garden wall in my garden adjacent to the garage (separated by a 1m wide path. The garage has an electric supply already but it needs upgrading as I believe it to be simply some twin and earth flat cable run from the house via a fused switch (about 10 - 15m).

My plan is to run a new supply using 4mm2 armoured cable from the house distribution board which has room for one more RCD. I will fit a 32 or more amp breaker in the consumer unit?

The 4mm2 armoured cable will then run along the side of the house, along the garden wall (The cream coloured wall on the right hand side of the pic above) to the workshop where it will slip under the facia board. It will then terminate in a small consumer unit which will provide power and light circuits to the workshop and power and light circuits for the garage. The garage power and light will then run under the cladding into some PVC piping into the ground, under the path and into the garage.

In the workshop I may have a 2.5 - 3HP compressor and possibly a Clarke 150 Amp Welder, the welder requires 15 amp min 230v single phase. Otherwise it will standard power tools. Workshop lighting will be a single strip light with additional mobile lighting over the work area. The garage will be converted to a computer / hobby electronics training / making area consisting of around 6 PCs a soldering station in total around 10 double sockets. The lighting in the garage will probably consist of 6 x remote controlled LEDs.

I have been seeking advice from my father in law who is now retired but has been an electrician for most of his life.

Questions:
1. For garages and garden workshops does the work need to conform to Part P of the electrical regulations?

2. Can I do it myself and not have it tested or do it myself and have it tested and certified?

3. Does my plan make sense?

4. For the garage I have been advised that I could run a single supply into the garage from the mini consumer unit in workshop terminating into a fused spur and from there split the sockets and lighting circuits.

 

[securespark]

Sounds like a commercial set-up?
A fair bit of load with welder and compressor that is hard-wired.
What size breaker is your F-i-L planning to protect the 4mm² SWA with?
And the 2 "power" circuits?

 

[Skavenger]

Sounds like a commercial set-up?
A fair bit of load with welder and compressor that is hard-wired.
What size breaker is your F-i-L planning to protect the 4mm² SWA with?
And the 2 "power" circuits?

Not commercial - just a dedicated / enthusiastic hobbyist
I was planning on a 30Amp or 45Amp breaker at the consumer board in the house supplying the 4mm2 then 30Amp in the dist board in the workshop supplying the garage (Then fused spur for power and lighting) and 30Amp / 15 Amp for the lighting / power for the workshop.

My preferred option though would be for a separate power and lighting supply going from the dist board in the workshop to the garage 30Amp and 15Amp?

 

[mattylad]

1) Have you read part P? if not read it, if so read it again.

2) yes, yes. (third option = do it yourself and have it tested but not certified). The 2nd option is the hardest according the the sparkies on here - finding one that will certify your work is not easy.

3) Yes it make sense. (I'm not saying its correct but makes sense.)
Where it runs into PVC pipe and into the garage, will this still be in armoured cable as its going underground? (AFAIK pvc pipe is not much protection against a spade going in the ground.)

4)Why not put a small consumer unit in the garage? with seperate MCB's for the sockets and lights?
This IMO would be much easier to reset when the lights or power goes off than a simple fused spur. (albeit initially costs more)

Did you remember where you left your tape measure?

 

[ban-all-sheds]

1. For garages and garden workshops does the work need to conform to Part P of the electrical regulations?

Yes, and it is also notifiable, so you are supposed to either use a registered electrician or apply for Building Regulations approval in advance.

2. Can I do it myself and not have it tested or do it myself and have it tested and certified?

The first thing you need to decide is whether you are going to comply with the Building Regulations or not.

If you are, and you want to DIY, then you will have to do whatever your LABC wants regarding testing. You will not (should not) be able to find an electrician to falsely clam that he did the work so that you don't have to apply for approval in advance.

3. Does my plan make sense?

I'm never a fan of supplying CUs in outbuildings from a house CU. Better, IMO, to supply them direct from the incoming supply via a switchfuse. I would advise having an electrician assess the load and do the design, otherwise the design part of the Electrical Installation Certificate (nothing to with Building Regulations notification) becomes a problem.

You would also be advised to discuss the welder with your DNO, because if you don't, and the use of it disrupts your neighbours' supplies, you'll be in trouble

4. For the garage I have been advised that I could run a single supply into the garage from the mini consumer unit in workshop terminating into a fused spur and from there split the sockets and lighting circuits.

Having an FCU for the sockets is a strange idea.

 

[JohnW2]

1) Have you read part P? if not read it, if so read it again.

Sound advice, but it doesn't take long to read, even twice ...

Reasonable provision shall be made in the design and installation of electrical installations in order to protect persons operating, maintaining or altering the installations from fire or injury.

... and that is all it says (other than notes about scope, which confirm that it applies to outbuildings etc. of domestic properties).

Kind Regards, John

 

[Taylortwocities]

My plan is to run a new supply using 4mm2 armoured cable from the house distribution board which has room for one more RCD. I will fit a 32 or more amp breaker in the consumer unit?

I have only read the first sentence in your post, which leads me to suggest (as i suspect others have) that you need a qualified electrician to do this. And this isn't you.

1. You say "room for one more RCD". Really? I would expect the consumer unit wopuld already have as many RCDs as it needs. Perhaps you mean MCB? Do you know the difference?
2. "32 or more amp breaker". Really? Do you know what the current carrying current of 4mm² SWA cable is? If its less than 32amp, then you could have a melty situation.

I'm sure you are a great handyman, and the woodwork on the workshop looks fine. But leave the lekky to an expert, please.

 

[Skavenger]

OK thanks for all the comments on here. I have had an electrician look at and quote for the job. The quote not broken down labour / materials but is out of budget.
I have costed up the materials and am looking at around £350.
The house CU is 100Amp Mains Switch with an 80Amp RCD protected section which is where I will run the (now 6mm SWA)from.
Sockets will be on 2.5T&E from a 32A MCB and light will be on 1.5T&E 6AMCB . Same for the garage.

What I am struggling with but will consult my sparky on is understanding what CU to fit in the wksp. Does the RCD on the workshop CU need to be lower than the supplying MCB. And what does the MCB at the supply end in the house CU need to be to cover both the wksp and garage 40Amp?

FYI on the above the Welder and Compressor are not hard wired they have both been running using a standard 13Amp Plug for about 4 years. The remaining power will be PCs, 3D Printer, TV, lighting etc. No electric heating or anything that is going to pull much current.

 

[winston1]

RCDs and MCBs are different things that do different jobs. This question: "Does the RCD on the workshop CU need to be lower than the supplying MCB." is meaningless. The RCD should be 30mA trip with a rating of at least as high as the MCB.

If the feed to the workshop is already protected by a RCD you don't need another in the workshop anyway.

 

[ban-all-sheds]

The first thing you need to decide is whether you are going to comply with the Building Regulations or not.

Not, it would seem.

So now you need to learn all the things you need to know so that you can do the electrical design and installation work you have decided to do.

The thing is installing new CUs, submains etc is not a trivial job, and I can assure you that it involves knowing far more than you think it does.

Asking questions here can be a useful part of a learning process, but they are not a substitute for proper structured studying. The key term there is "learning process" - you cannot learn all the things you need to know just by asking questions here. It isn't structured enough - it won't provide you with a way to progress where each step builds on what you learned before.

You can't carry out a job of this magnitude by asking whatever random questions happen to occur to you. You've already shown that you have some dodgy misconceptions - what if you get something wrong because you have no idea your knowledge is wrong? What if you miss something because you simply have no idea it even exists, and just don't realise you don't know it?

And then we come to testing. Do you know what tests you would carry out on the installation - what sequence you'd do them in and at what point you would energise the installation, and for each test do you know what is being measured, why it is important, how you would carry out the test, and with what equipment, and what sort of results you would expect to get if everything was OK?

I have had an electrician look at and quote for the job. The quote not broken down labour / materials but is out of budget.

I can dream up any number of home improvements which would be out of budget for me. So I'm simply not going to be able to have a 6m rear extension and a loft conversion, and that's all there is to it.

 

[ericmark]

As said not quite as easy as it looks, so 4 mm² at 32 amp design current which also feeds lights looking at maximum length of 20 meters to comply with volt drop regulation. In real terms needs to be less than 20 meters to allow for internal wiring of shed and garage.

Clearly to go over 32 A you would need heavier cable.

For an electrician where we have done the job many times we have a good idea of the readings we expect so we may not calculate unless we think on the edge, we measure after, however if you get it wrong, and it needs 6 mm² to comply with 32 A then although you can drop to 25 or 20 amp, that may mean your welder will not work.

So for you no short cuts, you have to work it out. Your allowed 3% volt drop for cables which supply lights, I wrote myself a program to work out volt drop, as the calculation is not simple, and too easy for a error to slip in when working it out.

I have done work under building control, and first question is what qualifications have you got. Yes theory you don't need to have passed any exam to be an electrician, but without exams it would need some other method to show you have the skill required, and your not likely going to be able to convince the LABC that you have the skill. Maybe your father-in-law can? But even then the cost is still around £100 to register the work, if they will not allow your father-in-law to do the inspection and testing, then you can double the price at least to have some one test and inspect. In general although rules say you can DIY the LABC don't want you to, so they will not make it easy. If anything fails, you pay again for extra visits.

I was lucky, work I was doing was for the disabled so was free of LABC charges. In Wales it is £100 plus vat for first £2000 worth of work, England varies county to county. And they wanted to see my test equipment so you will also need to buy, rent, or borrow, clearly has to be official as need calibration certificate, so can't unofficially borrow.

When my meters ran out of calibration and I tried to hire, I found not cheap, as each time hired out, they need recalibrating, so I would allow at least £500 to pay for LABC and meters, once you do that, then really you need to ask is it worth it? So when I wanted mothers house rewired, I got some one in, just not worth DIY even when you do have all the qualifications.

OK you could do it then get an EICR done after, may not be the legal way, but should satisfy insurance, but of course only if it passes.

The problem is a 13 amp supply using a FCU may not need notifying depending where you live, but will not allow you to use a welder. So when you consider buying a welder you need to add cost of getting a supply, at which point a engine driven one starts to look a better option.

If your going to break the law, then you should not be asking questions on here. Just like some one speeding should not post a traffic cam showing them doing it on facebook. OK don't think anyone would try to track you down, but if you make an error and anyone is injured then the HSE will investigate, so it needs to comply.

We know what you look like, we know what the shed looks like, we know you live in Devon, now you have posted a picture if anything goes wrong, then the HSE could well find this thread. Of course if nothing goes wrong they are unlikely to be worried.

 

[Taylortwocities]

RCDs and MCBs are different things that do different jobs. This question: "Does the RCD on the workshop CU need to be lower than the supplying MCB." is meaningless. The RCD should be 30mA trip with a rating of at least as high as the MCB.

If the feed to the workshop is already protected by a RCD you don't need another in the workshop anyway.

Agreed!!
@Skavenger if you run feed from the house CU it should come from a non-RCD protected way. Better for it to come from a completely separate switch/fuse.
Two RCDs in series is a difficult thing to achieve as true discrimination of RCDs is done on time, not current.