Should I install an RCD when replacing multi socket in garage?

Veteransaver

mark_cycling00 said:

Thanks for the replies it's a great learning experience.

If sounds like I could check to see if my consumer unit has RCBOs target than just fuses. If they are RCBOs then the circuit might be "safe"

The scenario I'm not sure about yet is as follows: if something dangerous happens to a power tool eg drill through a live wire. Will the entire garage circuit be affected? I'm just concerned about keeping the freezer working in this scenario 

Will a metal socket with built in RCD help at all?

Thanks

If your house consumer unit is fairly modern it will likely have mcbs for each circuit (these are just "fuses" really,) plus 1 or 2 RCDs as well protecting all the circuits too.
Alternatively it could just have rcbos on each circuit (rcbos are a combined MCB and RCD)
There is a possibility that the garage feed isn't RCD protected at all though and is just on an mcb, there are various reasons why it may have been done that way in the past Eg if it was to supply a freezer in a utility room, then the main house RCD tripping wouldn't take the freezer out (RCDs used to trip a lot eg if an incandescent bulb blew but it's not such an issue with CFL/less)
If you put a picture up of your consumer unit we would be able to tell.
It can be a good idea to also use a plug in RCD if using an electric power tool outside. Consumer unit RCDs can sometimes stick and fail.to activate, so a second one won't hurt, other than that a fault could activate either one of the RCDs (or both)
No real need to go for metal clad boxes though unless you think it's likely the socket will get damaged by whatever you are doing the garage!

Section62

mark_cycling00 said:

The scenario I'm not sure about yet is as follows: if something dangerous happens to a power tool eg drill through a live wire. Will the entire garage circuit be affected? I'm just concerned about keeping the freezer working in this scenario 

If you had some kind of accident like that (and assuming the garage is RCD protected) then you'd know because the power would go off.  All you need to do then (assuming it isn't the garage feed you've drilled into) would be to unplug/isolate whatever is damaged and turn the RCBO/RCD back on. The freezer shouldn't be affected for more than the time it takes you to turn the power back on.

It would be more of a concern if you intended to plug something in which was left on unsupervised - for example Xmas lights or a water feature.  These could trip the power off without you noticing for some time.  If the freezer isn't opened then it should be Ok for many hours without power though.

So, if you envisage using something unsupervised then it may make sense to have separate circuits for the freezer and general use socket, but then as the main consumer unit should be RCD(/RCBO) protected it probably won't make very much difference.

This is where RCBO's in the main consumer unit could have a benefit - if you arranged for the freezer to be on a separate RCBO protected circuit then you'd only have an issue with the freezer if the freezer circuit had a fault.

TBH without us knowing what the existing unit in the garage does, and how your main consumer unit is configured, the advice on this thread is largely guesswork.  You may want to get an electrician to take a look at what you have and what you need to do to get a safe result.

Edit:  I personally would use metalclad fittings in a garage for the added robustness.  They don't have to cost that much more than plastic.