Garage to be protected by an RCD

[ash88]

Hi,

I am an industrial electrician and have been asked by a friend to do some work on their house. I would like some advice on RCD's.

I have been asked to install a light and a socket in a garden shed. I am planning to supply the shed via the garage which already has a supply from a 32a breaker (which i am going to replace with a 20a breaker) seen as though it is run in 2.5mm SWA.

The garage circuit is currently not protected via any kind of RCD / RCBO. However, somebody has previously installed an RCD next to the house consumer unit, and has routed the house sockets circuit through it.

Will the RCD previously installed for the house sockets interfere with an RCD if I put one in a 4 way consumer unit in the garage?

Cheers.

 

[Mork]

Can you not connect the garage circuit on the existing RCD protected board?

 

[Brendan976]

You can do it that way, it just depends how much earth leakage is taking place. Why not put a garage consumer unit with an rcd in it, you don't need to rcd the supply swa.
Ben

 

[Des 56]

No it won't at least not by your description ,where would the imbalance arise?

 

[telectrix]

if both RCDs are 30mA, then no discrimination and a faulf in the garage takes out whichever RCD reacts first. not good if freezer circuit is disabled while away.

 

[Des 56]

if both RCDs are 30mA, then no discrimination and a faulf in the garage takes out whichever RCD reacts first. not good if freezer circuit is disabled while away.

installed an RCD next to the house consumer unit, and has routed the house sockets circuit through it.

The Rcd in the house will not come in to play tel if he has a separate garage supply

 

[telectrix]

was thinking he intended feeding from the RCD protected socket circuit. my bad, blame it on lack of beer; which omission will now be rectified.

 

[ash88]

http://img442.imageshack.us/img442/5835/20130414155600.jpg shows the separate RCD.

So it looks like im ok to install a 30mA RCD in the garage.

 

[telectrix]

are you thinking of coming off that spare way in the CU? if so, i'd consider 6mm SWA fed from a 32A MCB (you can still get them for that board), then RCD garage. 20A MCB for sockets and a 6A for lights. use adaptable boxes if necessary to gland the SWA. if it's PME earthing being used, make sure any extraneous metal parts are bonded back to MET in 10mm.

 

[valleybilly]

Is the garage separate from the house ?

 

[GLENNSPARK]

http://img442.imageshack.us/img442/5835/20130414155600.jpg shows the separate RCD.

So it looks like im ok to install a 30mA RCD in the garage.

as has been said...the problems arise when you have 2 RCDs of the same type installed in series....the issue being the RCD upstream will already be subjected to an amount of leakage....so a fault bottom end would take out the top end RCD first....but as you have pointed out...if its a case of only the house socket circuit that has been given additional protection (i`m assuming its TN earthing)...then it would be a requirement to use an RCD bottom end to provide additional protection for the outdoor equipment you plan to install

 

[ash88]

The garage is already wired in 2.5mm SWA from that 32A breaker in the picture, which I am going to downgrade to 20A.

 

[GLENNSPARK]

if the earthing arrangements are TT then a 100mA s type RCD can be installed top end to provide the discrimination....30mA bottom end to cover finals...

- - - Updated - - -

The garage is already wired in 2.5mm SWA from that 32A breaker in the picture, which I am going to downgrade to 20A.

yep.....makes you wonder though who thought it was acceptable to use the wrong choice and setting of OPD...lol.....

 

[ash88]

Cheers for the replies everyone, I was 95% sure but didnt want to install it all and then find the RCD's didnt like it.

Valleybilly, Yes the garage is a separate building to the house.

 

[GLENNSPARK]

Cheers for the replies everyone, I was 95% sure but didnt want to install it all and then find the RCD's didnt like it.

Valleybilly, Yes the garage is a separate building to the house.

whats the earthing arrangements here?