Garage Consumer Unit

[chrisd1980]

Hi
I'm looking to get my garage rewired. I'm not an electrician and, while I'm happy to do this myself, I'll get someone in with the right qualifications to do anything that is regulated. Before I do so I just wanted to check that my understanding is right and wondered if anyone would be able to comment.

Current setup is a single feed from the consumer unit in the house to garage via SWA that I suspect may only be 2.5mm. I'm not in a position to lay a new cable so will have to stick with that. Garage consumer is 10m from consumer unit in house (including vertical drops) and the cable is connected with a 16A mcb on the non-rcd part of the unit.

As I understand, 2.5mm (in a wall) is good up to 16A so that's ok.

In the garage I'm looking to have potentially four circuits:
Sockets - for a tumble dryer and to charge some drills etc. If I do use any tools, that'll be while tumble dryer is off.
Lights - no more than 500w in total, including outside lights.
Outside socket - max 5A
Shed - for some lights and a radio

Shed and outside socket will be no more than 6m (including vertical drop) from garage consumer unit.

I know that I can't run everything to the max but that's ok.

Questions I have are:
Is a four way consumer over the top, should I put shed and outside socket on the main socket circuit?
Do I need the incomer in the garage to be 16A? Seems obvious given house consumer is on a 16A.
Should breakers be RCD or RCBO or MCB?
What load breakers should I use - 16A on sockets, 6A elsewhere?

I know 6mm or 10mm would be much better but cannot upgrade the 2.5.
Thanks in advance.

 

[Taylortwocities]

The MCB at the house end can be changed to 20amp.

You'll only need a 2-way RCD protected "garage" consumer unit.
6A MCB for the lights
16A for everything else. They can all go on one radial circuit from the MCB. There's no point making it a ring.

Unless you have a TT supply, use a metal consumer unit like this
http://www.screwfix.com/p/mk-metal-...=Search-_-SearchRec-_-Area1&_requestid=106739

It will be easier to connect your SWA through the gland.

 

[ericmark]

Years ago with a 16A supply normally I would not bother with a consumer unit. A fused connection unit (FCU) switched would be used as light switch with a 3A fuse and no protection for sockets the 16A in house is good enough.

But today we need RCD protection so you have two options. Either a consumer unit or a RCD FCU the latter means max 13A.

In a garage I consider other factors as well. If for example your using a sander and power fails it is easy to forget to switch it off. So using active RCD's means when power returns the sander will not auto re-start.

 

[bernardgreen]

In a garage I consider other factors as well. If for example your using a sander and power fails it is easy to forget to switch it off. So using active RCD's means when power returns the sander will not auto re-start.

Or a fan heater as happened to a friend of a friend. A heater running continuously for three days before someone noticed the shed roof was drying very quickly after rain.

 

[JohnW2]

But today we need RCD protection so you have two options. Either a consumer unit or a RCD FCU the latter means max 13A.

I suppose that there is no theoretical reason why one could not have two or more RCD FCUs, although one then might just as well have RCD sockets.

In a garage I consider other factors as well. If for example your using a sander and power fails it is easy to forget to switch it off. So using active RCD's means when power returns the sander will not auto re-start.

True. However, whilst RCD adaptors and sockets (and possibly some RCD FCUs??) are often active, I don't think that active versions of RCDs to put in CUs/enclosures are 'freely available' are they? - I don't actually having seen any listed by the 'standard' wholesalers

Kind Regards, John

 

[ban-all-sheds]

I think that the first time someone came home from holiday to find a freezer full of rotting food, complaints from neighbours about their burglar alarm going off, and none of their TV programmes recorded, because their active RCD had turned a 2-hour power cut into a 2-week one they would realise the folly of having that sort in their CU.

Where there are genuine concerns about unattended machinery springing into life I think some kind of e-stop with a latching contactor would be more appropriate.

 

[JohnW2]

I think that the first time someone came home from holiday to find a freezer full of rotting food, complaints from neighbours about their burglar alarm going off, and none of their TV programmes recorded, because their active RCD had turned a 2-hour power cut into a 2-week one they would realise the folly of having that sort in their CU.

Indeed - and I assume that's why 'active RCDs for CUs' do not seem to be 'readily available' (I imagine that they probably do exist, if one looks hard enough).

Where there are genuine concerns about unattended machinery springing into life I think some kind of e-stop with a latching contactor would be more appropriate.

True - but in the context of a domestic garage or shed/workshop, if one is going to have to have an RCD, anyway, then it probably would make sense to just use an active one (if one could get it), rather than to have separate 'fail-safe' devices.

Kind Regards, John

 

[AndyPRK]

I would fit a CU to house the RCD. (A 40A one will do, which means its the maximum current its designed for)

And on this example I don't think a 4 way one would be silly (assuming it wasn't significantly more expensive that a 2 way)

 

[JohnW2]

I would fit a CU to house the RCD. (A 40A one will do, which means its the maximum current its designed for) ... And on this example I don't think a 4 way one would be silly (assuming it wasn't significantly more expensive that a 2 way)

Indeed. As I often say when people start going on about a CU 'not being needed' in a garage/outhouse, if there's going to have to be an RCD (in some sort of enclosure), then one might just as well also have a couple of MCBs (even if they could often be replaced with an FCU) and put it all in a 4-5 module enclosure (unless one wants to leave the lighting without RCD protection).

Kind Regards, John

 

[chrisd1980]

Thanks for all the replies on this topic. They've added a great deal of clarity on what I'm planning.
I hadn't considered the impact of appliances switching or not switching back on after a power cut. Just like when I turn car engine off with car radio volume up high.

Couple of points I thought of, if I up the breaker in-doors to 20A, would i match that on the incomer in the garage?

Someone mentioned putting in an earth spike for the shed, is that necessary? I'd have thought the breakers would kick in before that was needed.

Thanks again, really appreciate this guidance.

 

[Taylortwocities]

While I like to assist, you obviously do not have the level of competence necessary to do this.
At the beginning you said

Hi
I'm looking to get my garage rewired. I'm not an electrician and, while I'm happy to do this myself, I'll get someone in with the right qualifications to do anything that is regulated.

This work is regulated by Building Regulations Part P. That says that electrical work must be carried out safely, and you dont have the skills to do it.
Otherwise you would know about the curent capacity of the incomer (why would it need to match the feed MCB??)
And also you would know if a earth electrode is necessary, or not.

I suggest you find an electrician who is prepared to let you do some of the grunt work (but NOT the design). And who could test and check it all out.

 

[chrisd1980]

Thanks. Rest assured I'll be having someone qualified to do this but no harm in me asking in order to understand how it works.