2 RCDs same circuit

[Big Man]

Am wanting to put in a garage CU to divide up garden and garage lighting and power circuits. Currently power comes off kitchen ring that is already protected with a 30mA RCD. For sake of convienience to client, if mower trips RCD they can flick RCD back on at garage RCD rather than having to move furniture to get to main CU and also effecting kitchen appliaces. Has anyone had problems with problem tripping or test results being wrong. Or am I good to go down this route.

Thanks people.

 

[ezzzekiel]

there is no benefit of having two 30ma rcd in circuit.

 

[Big Man]

I appreciate that there is no benefit to this set up. The matter is one of convienience. The question concerns whether there would be a conflict between the two RCDs?

Btw the main CU only has one RCD so tripping that could cause havoc in the rest of property as runs multiple pc for office at home.

Your thoughts are all appreciated.

 

[Spudnik]

You cannot have 2 30mA RCD's in one circuit as there will be no discrimination between the two.

And more often than not, it will always be the main one in the house that would trip anyway.

Your only other solution would be to run in a new SWA from the house CU from the non RCD side and install as you are going to, an RCD CU in the garage.

 

[Big Man]

Thanks I thought there was something like that just couldn't remember what.

Thank you!

 

[claire_r]

I have tested these before, 2 rcds in parallel doing a 5 times test, one tripped, then the other, there is no discrimination between the two, whichever one is more sensitive will trip which is generally the house as Jason said.
I would split the main tails wire its own supply =0)

 

[harrymonkfish]

I have tested these before, 2 rcds in parallel doing a 5 times test, one tripped, then the other, there is no discrimination between the two, whichever one is more sensitive will trip which is generally the house as Jason said.
I would split the main tails wire its own supply =0)

if you chose this option, whats the best way to protect the swa cable going to the outbuilding?

 

[Spudnik]

if you chose this option, whats the best way to protect the swa cable going to the outbuilding?

With a standalone CU with a suitably rated MCB for the size of the SWA.

 

[harrymonkfish]

So does that mean you have would have 2 stand alone CU's? One at the house intake and one in the outbuilding?

Thanks
Harry

 

[Spudnik]

So does that mean you have would have 2 stand alone CU's? One at the house intake and one in the outbuilding?

Thanks
Harry

Yes you would.

Although the one for the garage would be considerably smaller.

 

[monkeyelectric]

How about the mcb for the swa protected by a 100mA rcd at the house and the 30mA in the garage? that way you protect the swa against fault and overload, or a time delayed rcd at the house end?you'll have your discrimination sorted

 

[harrymonkfish]

Yes you would.

Although the one for the garage would be considerably smaller.

The job I am planning for will be an extension separate from the main house. Ring, lights, shower and workshop.

So my plan is:

Split the tails at the intake into a Henley block.
63a MCB in stand alone CU.
10 mm2 SWA 2 core through house, buried for 2 meters max, into extension. 15 meters approx.
Small CU with 30mA RCD
Split into 1 ring, 1 lights, 1 shower 40A
Separate earthing via TT electrode 16mm2
Bonding to water intake 10mm2

Acceptable?

Harry

 

[Spudnik]

The job I am planning for will be an extension separate from the main house. Ring, lights, shower and workshop.

So my plan is:

Split the tails at the intake into a Henley block.
63a MCB in stand alone CU.
10 mm2 SWA 2 core through house, buried for 2 meters max, into extension. 15 meters approx.
Small CU with 30mA RCD
Split into 1 ring, 1 lights, 1 shower 40A
Separate earthing via TT electrode 16mm2
Bonding to water intake 10mm2

Acceptable?

Harry

Sounds good to me although...

Main earth could be dropped to 10mm (depending on tests) and main bonding to 6mm.

Dont forget to earth the SWA, preferably at both ends.

 

[harrymonkfish]

Thanks for that Jason.

Just one thing. I thought that as the earthing in the extension will be separate from that of the house, then the SWA should only be earthed at one end ie the house? I was under the impression that you cannot mix between different earthing systems.

Harry

 

[ezzzekiel]

is it totally seperate or attached? this is still a greyish area about exporting earths. prob best idea is to tt the extension