Garage electrics

[Rob]

I am going to build a new garage and I would like some advice on what electrical sockets I should go for. I will probably be getting welder and I may invest in some other bits and pieces like a mill/pillar drill/lathe. Seeing as I only have a single phase domestic supply what single phase sockets should I fit and how many? I am thinking of 1 x 32A and 2 x 16A as well as a few 13A double sockets for now but I am not sure if this would be sufficient or suitable.

Also, will a 30mA RCD be problematic with a welder? If so what can be done about it?

 

[Towpack]

If you're wanting 32,16 and 13A sockets on the same supply you really need a small consumer unit in the garage so they can all be fused (MCB's) at their correct ratings. The number of sockets is really down to personal preference/convenience. When I needed power in the shed at the bottom of the garden for sockets, pond equipment and lighting etc I ran (buried) an armoured cable from the main consumer unit in the garage via a 45A MCB and fitted a small consumer unit in the shed, then fed the 13A sockets and the lighting from this via the correct size MCB's. Personally, I've had no problems welding from a supply fed through a 30ma/30ms RCD although I have heard of some having problems with it.

 

[Iwan]

When I did the power supply in my garage next to my house. I wanted to do it to run my inverter welder.. quite high ampage welder. I later on fitted a double house style 3 pin socked, steel type run off a 16 amp rcd.
I have a 16 amp blue hubble outlet and run all my powertools with male hubbles.
For the welder have a 32amp hubble outlet but use a 40 ma rcd to run it off as the welder is rated above 32ma . It works without fail and most importantly the welder can run close to full bore!

With the 32amp outlet you can of course run a 2 x 16 amp splitter. With this setup there's more than enough power to run a garage comfortably. ..

 

[Towpack]

For the welder have a 32amp hubble outlet but use a 40 ma rcd to run it off as the welder is rated above 32ma . It works without fail and most importantly the welder can run close to full bore!

.

Are you getting ratings confused here? Do you mean a 40A RCD? 30MA is the current imbalance (effectively leakage to earth) required to trip the RCD. 32A or 40A etc is the max current draw of the circuit your feeding. An RCD with 30ma/30ms trip is (or was) the standard for protection against electrocution. JMO

 

[Iwan]

I'd say I was! I am not an electrician! My qualified friend installed the setup. Sorry about that! Lol it works well though. .

 

[moggy1968]

There is a good chance your standard 30ma rcd will trip with your welder on start up.

I would run a seperate supply to your garage from your main consumer unit. I would use SWA for that so you don't have to use an RCBO and cover it for overload protection with a 63a MCB. If you can't fit it to the consumer unit then you would need to split the meter tails in a henley block and put is a little sub board.

In the garage you then have another consumer unit. rather than using a single 30ma RCD to protect all the circuits and MCBs for overload protection I would go for an 6a RCBO for your lights, 16a radial circuit (i.E not a ring) for the sockets and then use a 32a(or whatever the manufacturer of the inverter suggests) for the welder, but for this rather than using a domestic B type I would use a commercial C type RCBO. Mate this to a suitably rated commando socket.This is not the cheapest solution, but is, IMHO, the most useable with the best discrimination of your circuits. It's the exact same setup I used for a customers garage when I was a sparky and it worked a treat.

If you need more sockets of over 13a then just fit a couple of 32a commando sockets. Other than cost there is no real point in using 16a ones. Just go for 32s and leave yourself some extra capacity. bear in mind, each of those sockets will need a suitably rated isolator as well.

All of this is, of course, part P notifiable so needs to be done by a registered spark!

 

[Rob]

Thanks for the tips. Yes I will be installing a CU in the garage with an adequately sized SWA (armored) cable buried in the ground. I'm not too bothered about advice on how many 13A sockets to install as like most people, we all know how many 13A sockets we need. However as I have not used much 16A or 32A garage/workshop equipment I do not know if 2 x 16A and 1 x 32A socket will be sufficient.

Every domestic socket these days requires an 30mA RCD so I was wondering if this will cause any issues with welders. I will definitely be wiring the 32A socket via a dedicated 30mA RCD/RCBO to minimise the impact when it does trip.

 

[moggy1968]

Thanks for the tips. Yes I will be installing a CU in the garage with an adequately sized SWA (armored) cable buried in the ground. I'm not too bothered about advice on how many 13A sockets to install as like most people, we all know how many 13A sockets we need. However as I have not used much 16A or 32A garage/workshop equipment I do not know if 2 x 16A and 1 x 32A socket will be sufficient.

Every domestic socket these days requires an 30mA RCD so I was wondering if this will cause any issues with welders. I will definitely be wiring the 32A socket via a dedicated 30mA RCD/RCBO to minimise the impact when it does trip.

I think your confused between an RCBO and an RCD and an MCB. an RCD protects you from electrocution, and MCB protects the circuit from overlaod, an RCBO does both, so if you fit an RCBO for your sockets that satisfies the RCD requirement and seperates it from your welder circuit so you don't get nuisance tripping on your sockets. As I have described above, if you try and use a 30ma B type RCD for your welder, it will probably trip.

 

[Rob]

Thanks for the post Moggy, really useful. I thought that B/C type only applied to MCBs? Presumably a C-type RCBO would take longer to trip than a B-type RCBO under say a 100mA current leak condition and therefore would be less likely to trip when you start up a large inverter?

I am aware of the part P building regulations, I am exploring the option of getting building regulations to certify the wiring for me as I am not a "registered competent person". Need to confirm the cost first as it is unclear.

 

[Rob]

I think your confused between an RCBO and an RCD and an MCB. an RCD protects you from electrocution, and MCB protects the circuit from overlaod, an RCBO does both, so if you fit an RCBO for your sockets that satisfies the RCD requirement and seperates it from your welder circuit so you don't get nuisance tripping on your sockets. As I have described above, if you try and use a 30ma B type RCD for your welder, it will probably trip.

I did not see you post before I posted. Well aware of the difference, I design all aspects of motor test rigs at work which run off 3 phase.

 

[moggy1968]

I did not see you post before I posted. Well aware of the difference, I design all aspects of motor test rigs at work which run off 3 phase.

yes, a C type shouldn't trip as easily as a Btype, but they aren't cheap.

Getting building control in is expensive, and they will probably want to visit more than once.

better to find a tame electrician who will let you help with the work to keep costs down.

 

[moggy1968]

There is a provision for specifically labelled sockets to be used without RCD protection (usually freezers) providing the cables don't require RCD protection under the regs and disconection times are met., so it might be worth having the conversation as to wether they would let you do that with your welder. They probably won't, they'll just tell you to pay the money for the right RCBO, but it might be worth asking!

 

[frank rabbets]

Are re you worried about the RCD in the house being affected?

 

[Rob]

No, just the RCD or RCBO whichever I will end up using on the 16A and 32A sockets. The garage feed will be going via an MCB in the house bypassing the RCDs in the main consumer unit.

 

[frank rabbets]

I guess the larger and more powerful a machine the more will be leaking to earth. Therefore a tripped rcd does not necessarily point to a fault ? I'm just trying to learn. I bet a lot is lost in a power station.