RCD - where would you place them?

[OtleySpark]

Going to replace my consumer unit and also place a secondary one in the garage.
I understand it's not good to have 2 RCDs on the same circuit (unless there is discrimiation between them) so I was wondering where would you put one to safeguard the garage: in the main CU or just in the garage?
Does it make much difference how close (in a domestic situation) the RCD is to the point of use?
Thanks

 

[wingcoax]

The only place for an RCD is on the main Cu.BUTare you aware that this is not a DIY job? You need to notify your local building control and pay the required sum of money. You will be cheaper (a yorkshireman) to get a local registered electrician in.

 

[OtleySpark]

The only place for an RCD is on the main Cu.BUTare you aware that this is not a DIY job? You need to notify your local building control and pay the required sum of money. You will be cheaper (a yorkshireman) to get a local registered electrician in.

I have just qualified (and going through the registration process with NICEIC) so I can do it myself, but I was wondering what others thought?

 

[RF Lighting]

You should fit the RCD as close to the point of use as you can.

Assuming the supply to the garage is SWA and doesn't require RCD protection, then fit the RCD or better still RCBOs in the garage CU.

 

[plugwash]

The only place for an RCD is on the main Cu]

BS, putting the RCD in the garage CU or using RCD sockets is perfectly acceptabe as long as any non-RCD protected concealed cables are installed in an appropriate manner.

Personally i'd say it's better to have the RCD protection at the garage end as it's easier to reset when some leaky tool trips it. I''d also strongly consider having the lighting either not on RCD at all or on a seperate RCD from the sockets.

 

[JohnW2]

Assuming the supply to the garage is SWA and doesn't require RCD protection ....

Do you regard the mechanical protection afforded by the armour of SWA to be adequate to remove the need for RCD protection, or do you feel that the requirements for ADS (i.e. 'disconnection times') also have to be satisfied? I'm thinking of TT installations where I would have thought that there would be a requirement for RCD protection (time-delayed would do, to help with discrimination, if there were RCDs/RCBOs in the garage) upstream of the SWA.

Kind Regards, John

 

[Chri5]

Lets not forget than a feed than rcd at the board will trip other circuits on that RCD.

You could provide a type C RCBo on the direct side of the cu that feeds the shed circuit.

You could run from a Henley direct to the shed and avoid the house cu all together.

 

[Spark123]

What is the supply earthing type? Are there any non-RCD ways in the CU?

 

[JohnW2]

Lets not forget than a feed than rcd at the board will trip other circuits on that RCD. You could provide a type C RCBo on the direct side of the cu that feeds the shed circuit.

As far as I am aware, a Type C RCBO has the same 'RCD' operating characteristics as a Type B one. As I wrote above, if one needs RCD protection upstream of the SWA (or whatever) to protect the cable and wants to get discrimination from RCDs in the garage, one needs a Type S (time-delayed) RCD (not in a circuit protected by the CUs RCDs). I've never heard of a Type S RCBO, but maybe they exist.

Kind Regards, John

 

[JohnW2]

I''d also strongly consider having the lighting either not on RCD at all or on a seperate RCD from the sockets.

As RF has said, the best solution to that is probably to use RCBOs in the garage.

Kind Regards, John

 

[OtleySpark]

What is the supply earthing type? Are there any non-RCD ways in the CU?

I've been looking at CUs with a mix of non-RCDs and RCD controlled ways (one of the reasons for the OP).
The supply is TN-S.

 

[JohnW2]

I've been looking at CUs with a mix of non-RCDs and RCD controlled ways (one of the reasons for the OP). The supply is TN-S.

In that case,I would have thought the way to go would be to feed from a non-RCD protected way of the CU (with SWA feeding the garage, and any other cabling in the house installed so as not to require RCD protection), with an RCD (or, better, RCBOs) in the garage CU.

Kind Regards, John

 

[OtleySpark]

I've been looking at CUs with a mix of non-RCDs and RCD controlled ways (one of the reasons for the OP). The supply is TN-S.

In that case,I would have thought the way to go would be to feed from a non-RCD protected way of the CU (with SWA feeding the garage, and any other cabling in the house installed so as not to require RCD protection), with an RCD (or, better, RCBOs) in the garage CU.

Kind Regards, John

Yes, that's the conclusion I was coming to.

Thanks for people's replies.

 

[RF Lighting]

Make sure you properly test for Ze before you start work. There's loads of duff TN-S supplies around Otley, especially if it's a cast iron cutout in a damp cellar.