Extended electrics in the garage

[ptjs1]

Hi, I wonder if anyone can give me a bit of advice, please.

My garage has a power supply from a dedicated 16a RCB on the consumer unit in the house. The circuit is one of six in the CU protected by a RCD.

The wiring to the garage is 2.5 T&E going to a separate CU. This CU has two RCBs and plenty of space for more One is 6A powering feeding what was a single switched light bulb. The other is a 16a circuit which feeds a single socket, into which is plugged the electric garage door motor and then goes on to a twin outlet socket. Both the CUs are Memera 2000. The power cable going to the garage then goes onto an additional outbuilding which in turn has another Memera CU which has a 6a light circuit with a single switched bulb and a 16a power ciuit with one twin outlet. There is no space for further RCBS in this CU.

Hope that makes sense so far.

I have extended the garage light circuit to now have 3 fluorescent tubes instead of the original single light bulb. I now wish to install a further six double sockets in the garage. So, a couple of questions:

Could I just run all the additional powert outlets from the existing twin outlet? If so should I change the 16a garage RCB for a 32a one and also change the 16a House RCB for a 32a one?

or

Would it better to run an additional RCB in the garage CU and then run a ring for the new power outlets? If so, would a 16a RCB suffice, and then should I change the 16a RCB in the House CU for a 32a one?


I also would like to run 3 more twin power oulets in the other outbuilding. Again could I just extend the existing power outlet with the new ones and should I then change the 16a RCB in the outbuilding for a 32a one (I guess I will definitely have changed the 16a one in the house CUfor a 32a one) ?

Thanks in advance for any comments from anyone.

Paul

 

[streetlighter]

Theres no discrimination between the 16amp mcb feeding the garage CU and the 16amp mcb for the garage sockets. Id change the mcb in the house CU feeding the garage for a 20amp a 32amp would not protect the 2.5mm cable.

 

[nozspark]

You cannot change the house 16A MCB for a 32A as the cable cannot take 32A, at most you could supply 2.5 t&e from a 20A MCB as previously said.

As for how many sockets you want, that is not really the question!!

What you really need to be asking is can you use what you want to on a circuit supplied from a 16A or 20A MCB....... we need to know what you will be doing in the garage/what equpiment you will be using before we can help you much more.

After working out what your demand is going to be you may find that you can run everything you need off a 10A MCB or you may find that you need a new sub main running to your garage.

 

[ptjs1]

Tks for the replies guys.

Sorry, I realise that I should have indicated what I wanted to run. The number of sockets is more about having them in convenient places rather than any belief that I'll be using a dozen appliances at one time. Also, there is unlikely to be anything running permanently other than a 2a battery charger. The sort of things that I run are:

- a 300w bench grinder
- a 300w bench polisher
- an electric drill
- a 3hp compressor
- a charger for a rechargeable 18v drill
- a 2kw heater (that's probably the biggest load, but isn't on very often, only for an hour or two in very cold weather)
- an extension lead for a Flymo lawn mower
- a trickle battery charger (2a max). Running in very low-draw trickle mode most of the time for my motorbike
- a booster battery charger. Used once in a blue moon but I guess for very short periods it can pull high current loads if jump-starting a car.

Apart from when the heater might be on, it's unlikley that more than two or three of these things are on at the same time.

Does that help paint a picture?

Tks again

Paul

 

[nozspark]

Right then,

As you said it is unlikely that you will be using many things at a time you could say that the main items that could be running at a time are:-

2kw heater
3hp compressor
300w drill or polisher

this makes your demand to be 5300w or 22.08A and this is without lighting or your battery chargers. I would therefore think that you might be better if you run a new 40A sub main to your garage and split it into a 32A circuit for your sockets and a 6A circuit for you lights.

Whether you run your socket circuit as a ring or a radial is up to you, but you will need to size your cables appropriately.

BTW... this work comes under part p of the building regs

 

[ptjs1]

Tks again for the replies.

Obviously a 2kw heater running at full power loads up the circuit considerably and starts to test the capacity of the existing 16a protection in both the garage mcb, and the rcd-protecetd house mcb, if I am using other equipment at the same time

This is also the first time that I've encountered the issue of Part P, not having done anything significant on the diy electrical front for the last couple of years.

Having downloaded the relevant doc and also looked thru' a number of threads on this forum where people have debated whether a piece of work is covered by the regs, can I please ask what seem to be a few simple questions (but might not have simple answers!):

- If I accept the limitations of not being able to have a hi-power heater running with other equipment as well, is it acceptable for me to run six additional double sockets in my garage, spurred (or is the new term 'radialled'?) from my existing double socket, leaving the existing mcbs in place, without having to either notify anyone or get the work undertaken by a qualified person? My (perhaps naive) reading of the regs is that this would be fine.

- Am I allowed to convert the existing garage circuit to a ring, again doing it myself and without notification and inspection or does running the new wire back to the cu constitute a "new circuit" which is subject to being undertaken by a qulified person?

- Following from that, is changing a mcb from 16a to 20a a task that I can undertake myself as well?


Tks again for all your input. I'm very grateful that people are preared to give up time on a Sunday to help me.

Paul

 

[luminaire]

Personally, I think you should get a local electrician to have a look at it.
2.5mm is not sufficient for your needs. It probably should be run in SWA anyway. Is it PME or TT?
It's probably better for you to have someone have a good look at the whole system.

 

[mdbalson]

What no one has asked yet is wether the garage is part of the house/ right next to the house, or seperate from the house.

If the garage is part of the house/ right next to the house, then it would not have to be wired in SWA would it? But if the garage is seperate from the house, then it would have to be wired in SWA.

 

[nozspark]

Tks again for the replies.

- If I accept the limitations of not being able to have a hi-power heater running with other equipment as well, is it acceptable for me to run six additional double sockets in my garage, spurred (or is the new term 'radialled'?) from my existing double socket, leaving the existing mcbs in place, without having to either notify anyone or get the work undertaken by a qualified person? My (perhaps naive) reading of the regs is that this would be fine.

- Am I allowed to convert the existing garage circuit to a ring, again doing it myself and without notification and inspection or does running the new wire back to the cu constitute a "new circuit" which is subject to being undertaken by a qulified person?

This depends on whether your garage could be defined as an outside space and hence become a special location in the eyes of part p

- Following from that, is changing a mcb from 16a to 20a a task that I can undertake myself as well?

Changing an OCD's value for a circuit definately comes under part p and it's value depends on several factors including cable size, length, where the cable is run, maximum demand (but to name a few) of the circuit in question. The OCD is only there to protect the cable and nothing else so you have to do some calculations before altering it!

Also if you are having any rotating machinery in the garage then you should not use standard flourescent light fittings and you should also consider whether you use a latching or non-latching RCD.

Really you should get an electrician in to do this job, if the finances are tight then maybe he/she will allow you to do some of the donkey work in preparation for when they turn up!

 

[davelx]

Approved doc P Page 8:

"f. Detached garages and sheds are not special
locations. Work within them is notifiable only
if it involves new outdoor wiring."