Adding more sockets to the garage. Where to begin?

[Taylortwocities]

4th one from the right is marked "garage supply" - as far as I know, this is the source.

OK, from what I can see from your picture, the MCB is a B16?? And probably on the RCD side of the board (again, need to see inside to be absolutely sure). It means that 16amps is the max total current you can pull on all of the garage circuits.

I suspect that only the freezer is RCD protected at the moment, as someone has gone to the bother of labeling that socket where no others are labeled.

Easy way to find out is to switch that MCB off and see if the freezer turns off!

 

[CovBoy]

Hi, yes it's B16.

So I looks like I need an electrician to do the following

1. Upgrade from 16amp to 20amp (confirming that the cable running from house to garage is sufficient)
2. Confirm if the garage supply is RCD, else swap it to RCD

...and only then can we really discuss next steps?

Thanks

Ben

 

[CovBoy]

*I made a mistake earlier in the thread - the switch fuse is ahead of the lights rather than the sockets.

 

[SimonH2]

There is an argument for not RCD protecting a garage/workshop/shed supply at the house IF the cable type/routing is suitable. That way, you are less likely to be left in a dangerous environment, holding a still spinning power tool, when the lights have gone out. Then put the RCD downstream of where the lights are teed off the supply.

 

[JohnW2]

There is an argument for not RCD protecting a garage/workshop/shed supply at the house IF the cable type/routing is suitable. That way, you are less likely to be left in a dangerous environment, holding a still spinning power tool, when the lights have gone out. Then put the RCD downstream of where the lights are teed off the supply.

A reasonable argument, but I don't think that is hardly ever done as you suggest. If the circuit is not RCD protected at the house end (with the caveats you mention), the 'solution' is almost invariably to install a 'garage CU' (with RCD incomer) in the garage/shed/whatever, in which case the feed to lights will be downstream of the RCD.

As with all similar situations we discuss, exactly the same could happen with a power cut (lights off and tools running down) and (if one is concerned about the very small risk) the only effective way of protecting against that is to have battery-backed up emergency lighting.

Kind Regards, John

 

[SimonH2]

Indeed, which just demonstrates that few people actually think about what they are installing and why - like the people who wired my mum's new house with no provision for electric cooking
Personally I'd put a couple of RCBOs in a 2way CU for that reason.

 

[JohnW2]

Personally I'd put a couple of RCBOs in a 2way CU for that reason.

That would certainly address the precise issue that concerns you but, as I said, if you are concerned about holding power tools in the dark whilst they run down, you need to install battery-backed-up emergency lighting, in case the situation arises as a result of a power cut or some problem with the circuit.

Also don't forget that, although these discussions always seem to major on RCDs, unless you have two separate feeds (with different OPDs in the house) to the garage/shed/whatever, both lighting and sockets in the outhouse are protected by the same OPD (in the house) - again raising the possibility that a fault in something plugged into a socket would very probably take out lighting as well (since discrimination may well not be achieved with the standard sort of arrangement). Again, emergency lighting is the only foolproof guard against that.

Kind Regards, John

 

[SimonH2]

All good points, but I'd counter that there's a balance to be found. There are lots of things you can do, it's a matter of doing those things that are either fairly easy and/or cheap to do or which address the most serious risks. In extreme, you'd simply not have any electrical supply at all as that's the only way to completely eliminate all electrical risks.
In my experience, it's the RCD that creates the most interruptions by a good margin, and in most cases it's easy to design out the problem of the RCD taking out lights as well as power.
I'd argue that emergency lighting is far from foolproof - without maintenance (specifically testing/replacing batteries), it's fairly likely that when it comes to be needed, it just won't work.
So I'd go for separate RCDs for lights and sockets - because in many situations it's easy to do and fairly inexpensive if "designed in" from the outset. Emergency lighting would probably be a close second on my list for various reasons. But these are all decisions to be made on a case-by-case basis.

 

[JohnW2]

All good points, but I'd counter that there's a balance to be found.

Indeed, particularly since we are talking about events which are incredibly small in the first place - the probability that one would be holding an operating power tool, or being very close to an operating machine tool, at the very moment the lights go out is going to be incredibly small.

In my experience, it's the RCD that creates the most interruptions by a good margin ...

Whilst I would agree with that in terms of 'domestic appliances', I'm far from sure that the same is true of portable or workshop power tools.

So I'd go for separate RCDs for lights and sockets

.... fair enough - but, although I understand your reasoning, I think it is extremely unusual to find anyone actually doing that for a garage/shed/whatever supply.

Kind Regards, John

 

[SimonH2]

Whilst I would agree with that in terms of 'domestic appliances', I'm far from sure that the same is true of portable or workshop power tools.

It's my experience - in a workshop with a variety of machinery including DOL started motors (compressor is 3hp, I suspect the saw bench is as well), MIG and stick welders, I don't recall having blown a fuse or tripped the breaker (rewirable fuse in the garage, B32 MCB in the house). But I do recall a few occasions* where the RCD (at the garage end of the supply) has tripped.
And it doesn't have to be while actually using a tool. Having to navigate the workshop in the dark, when you may have bits of work in progress, cables, hoses, etc lying around is a significant hazard. As you point out, emergency lighting would be "a good idea", but I suspect that in most domestic environments, they'd get even less attention to maintenance than smoke detectors

I think it is extremely unusual to find anyone actually doing that for a garage/shed/whatever supply.

There are lots of things that make sense but aren't commonly done.

* OK, most of these have been due to (we assume) damp in outside lights.

 

[JohnW2]

It's my experience - in a workshop with a variety of machinery including DOL started motors (compressor is 3hp, I suspect the saw bench is as well), MIG and stick welders, I don't recall having blown a fuse or tripped the breaker (rewirable fuse in the garage, B32 MCB in the house). But I do recall a few occasions* where the RCD (at the garage end of the supply) has tripped.
* OK, most of these have been due to (we assume) damp in outside lights.

I think that footnote is important'. I am struggling to personally recall any occasion on which a power tool/machine has tripped an RCD but, as you say, RCD trips due to external lighting etc. do occasionally happen.

IF one did as you suggest, and IF those external lights were supplied by the garage/whatever 'lighting circuit', then that would surely create an even more dangerous situation? - the garage/workshop lights would go out, but machinery/tools would carry on functioning normally. If lighting and sockets circuits had a common protective device, at least the lighting fault would also take out the supply to the tools/machine, so one would only have to wait (in the dark) for them to 'spin down' for the environment to become fairly 'safe'.

And it doesn't have to be while actually using a tool. Having to navigate the workshop in the dark, when you may have bits of work in progress, cables, hoses, etc lying around is a significant hazard.

True - but, as above, provided lights and sockets were not on separate RCDs, one would only have to wait (in the dark) for everything to 'spin down'.

There are lots of things that make sense but aren't commonly done.

Indeed - but, as I think I have illustrated above, there are definite 'swings and roundabouts' issues to be considered when deciding what does "make [more] sense".

As you point out, emergency lighting would be "a good idea", but I suspect that in most domestic environments, they'd get even less attention to maintenance than smoke detectors

Agreed. However, there are ways in which one can, if one wants, attempt to compensate for that aspect of human nature. Many moons ago, I devised an "emergency light" which had a delay (about 30secs IIRC) on 'switch on', with the permanent live feed disconnected during that delay period. Hence, if the (battery) light did not come on immediately one switched the light on, one knew that the unit required attention!

Kind Regards, John