RCD on garage feed.

[andcop]

I have just had 2 new CU's installed in my basement. All tested well.
The feed to the garage is from a 45A MCB and its own 30mA RCD via 6/10mm T&E running the length of the house into a junction box then a section of armoured under a path.
The garage already had a protected CU, with all circuits on an RCD except one for an alarm on an RCBO so that any nuisance tripping would not upset the alarm.
On test the circuit tripped within spec with both RCD's tripping every time.
My concern is that I have now lost the benefit of having the RCBO on the alarm circuit as if there is a fault on another circuit in the garage (outside light for instance) it will take out the whole feed to the garage.
I understand that to do away with the RCD on the feed to the garage I would have to have the whole run replaced in armoured cable. This is possible but likely to be expensive and not easy.
Someone made the suggestion of fitting a 50 or 100mA RCD in the main feed to the garage.
Any thoughts?

 

[RF Lighting]

Is the T&E feed to the joint enclosed within the fabric of the building, or is it run on the surface such as clipped direct or in trunking, conduit etc.?

 

[ericmark]

You can get 10ma RCD's and also not all RCD's are equal the X-Pole claim to not trip as often.

There was no need to put garage feed on the RCD but now on a RCD to revert back would in theroy mean one of the special cables or surface cable. Does not need to be SWA can use Ali-tube. Much depends on where the cable runs if not buried it does not need RCD and if buried more that 50 mm does not need RCD.

However when buried less than 50mm the RCD has to be a 30ma type.

 

[EFLImpudence]

I understand that to do away with the RCD on the feed to the garage I would have to have the whole run replaced in armoured cable.

Not necessarily but probably easier.
It could be -
run in earthed metal protection of one sort or another
buried in the wall deeper than 50mm. - not possible in brick/block construction.

or, of course, be visible - surface clipped or in trunking.

This is possible but likely to be expensive and not easy.
Someone made the suggestion of fitting a 50 or 100mA RCD in the main feed to the garage.

No.
If RCD protection is required it shall be 30mA.