Garage 16A Socket Cable&MCB Ratings?

[D.I.Y-SI]

Hi all,
I want to rewire my detached garage and install a new CU and 16A socket for my mig welder. The supply to the garage will be directly from the house CU which is about 2-3m away from the garage CU and is feed through conduit. In the garage I will have 1X 13a double socket, 1X strip light and 1X 16A socket. I will be using various power tools(SDS Drill, Small grinder, router ect.) on the 13A radial circuit plus the garage roller shutter door(plugged in), and on the 16A circuit a will be using a clarke mig welder(MIG160TM) which is rated at 16A( in the instructions is says not suitable for use with a 13a plug-'This welder must be connected to a 230v (50hz) supply, having a rated capacity of greater than 13 amps). I have trawled through many forums and cannot get a definitive conclusion on the cable/MCB sizes ect.

Here is my plan so far:

Starting from the house CU-there is already a 20A MCB type B installed for the garage should I keep that?
6mm T&E cable(length would be about 2-3 meters CU to CU. Leading to a 4way CU(1X63A 30MA RCD,3 MCB's).
For the 16A socket I would run from a 16A type C MCB to the blue 16A socket in 2.5mm T&E(distance about 4-5 meters in plastic conduit).

For the 13A circuit I would use a 16A type C MCB on 2.5mm T&E on a radial circuit which will be about 4-5 meters in length in plastic conduit.

If there are any sparks in here can you please tell me if this setup is correct or wide of the mark?
I will be getting it checked and will have a periodical check at the same time.
Thanks in advance

 

[ban-all-sheds]

I have trawled through many forums and cannot get a definitive conclusion on the cable/MCB sizes ect.

Well you've finally come to the right place, for here is all the information you need to form a definitive conclusion:

• http://www.google.co.uk/search?q=cable+installation+methods+17th+edition
  
• https://www.diynot.com/wiki/Electrics:MCBtoCable
  
• http://www.tlc-direct.co.uk/Book/4.3.1.htm
  
• http://www.tlc-direct.co.uk/Book/4.3.11.htm
  
• http://www.tlc-direct.co.uk/Book/5.3.1.htm
  
• http://web.archive.org/web/20070327014113/http://www.kevinboone.com/cableselection_web.pdf
  
• http://www.tlc-direct.co.uk/Technical/Charts/VoltageDrop.html <- Specify 2-core cable and PVC, even if that is not what you are using or it will make invalid assumptions.
  
• http://electrical.theiet.org/wiring-matters/28/appendix4.cfm?type=pdf
  
• http://electrical.theiet.org/wiring-matters/40/appendix-4.cfm?type=pdf
  
• http://www.batt.co.uk/upload/files/4d5.pdf
  
  The references above which are in italics are either out of date or incomplete. The principles are still valid, and you can absolutely learn valid things from them, but you will need to refer to the latest edition of the Wiring Regulations to get the correct data.

Starting from the house CU-there is already a 20A MCB type B installed for the garage should I keep that?

If you want to be the designer, then only you can decide that. Nobody here will be able to sign this:

I being the person responsible for the design of the electrical installation (as indicated by my signature below), particulars of which are described above, having exercised reasonable skill and care when carrying out the design hereby CERTIFY that the said work for which I have been responsible is to the best of my knowledge and belief in accordance with BS 7671:2008, amended to 2015 except for the departures, if any, detailed as follows:​

so you really have to become competent to do the design yourself.

6mm T&E cable(length would be about 2-3 meters CU to CU. Leading to a 4way CU(1X63A 30MA RCD,3 MCB's).

No RCD in the main CU? If there is, what are your expectations for how two in series will behave?

For the 16A socket I would run from a 16A type C MCB to the blue 16A socket in 2.5mm T&E(distance about 4-5 meters in plastic conduit).

This would be a good place for you to start: https://www.google.co.uk/search?q=mcb+discrimination

For the 13A circuit I would use a 16A type C MCB on 2.5mm T&E on a radial circuit which will be about 4-5 meters in length in plastic conduit.

You've checked that your fault loop impedance will be low enough to allow sockets on a Type C? https://www.diynot.com/wiki/Electrics:MCB2

If there are any sparks in here can you please tell me if this setup is correct or wide of the mark?

It has a number of flaws.

I will be getting it checked and will have a periodical check at the same time.

That isn't going to work. This is notifiable, so if you do it you need to apply for Building Regulations before you start, and when doing that you'll need to tell Building Control how you intend to comply with the regulations.

The thing is installing new CUs, new circuits, 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?

You need to either put this project on hold while you take a step back and spend some time learning and becoming competent to answer all your questions yourself, or you need to have an electrician do it. But please note that even when you have become competent to DIY, the notification issue could still make it more expensive for you to DIY than using an electrician.


And above all, before you do anything else, or invest another penny, you need to get approval from your DNO for the use of that welder, or you might find that you go to all the trouble and expense of setting up this garage only to have them tell you that unless you stop using it they will disconnect your supply.

 

[D.I.Y-SI]

Thanks for the reply, I think I will get a spark to carry it out then as it sounds more complex than I thought. But just for my curiosity could you tell me hypothetically what is wrong with my design if I were to use a 16A type B MCB on the 13A circuit and the main house CU is a split board with the existing garage feed on the RCD side which is 80A/30MA. The new garage CU would have been had I not decided to get a professional in a 63A/30mA RCD. Would there be any discrimination issues there? As a layman I would have thought the garage RCD would trip first?

 

[ban-all-sheds]

They are both 30mA devices - the 80A/63A rating is how much they can switch, nothing to do with tripping current.

With 2 in series either or both will trip.

 

[D.I.Y-SI]

I can see why they say what they say about you on the other forums now. Cheers

 

[Simon35]

I can see why they say what they say about you on the other forums now. Cheers

BAS has told you what you should do to do this properly. You maybe didn't know that it would involve so much knowledge and effort.

Whether you choose to do it is entirely your choice, but don't blame the messenger. Not least, because I doubt he GAF.