Is it permissable and/or advisable to simply replace the main isolator switch with a RCD of the same or higher rating eg.60 Amp and

what are the pros and cons of doing this ?

If allowable, and the RCD is physically the same size as the main switch, it would be a quick solution to 'upgrade' and make many installations a lot safer.

Also, is there a standard rail mounting method (IEC spec ?) or do the different manufacturers of the consumer units or 'fuseboxes' eg. Square D etc. have differing fixing methods for their circuit breakers ?

I also looked at this option. RCBO in stead of RCD though, as that has the over current protection as well. But I found a complete safe t cut RCBO being the same price as a rail mounted RCBO.

Certainly permissable as you can buy the parts. Just make sure you have a brand that is stocked in Thailand.

Pro - looks a lot neater, as everthing is enclosed in one enclosure

If you are replacing your incoming breaker you need to use an RCBO to retain over-current protection.

This can be problematic (expensive) if you have one of the distribution boards using plug-in devices (e.g. Square-D) in which case a front end RCBO (Safe-T-Cut) or a DIN mount RCD (you are retaining the existing main breaker so that will provide over-current) in a simple plastic box is a cheaper, but less pro looking solution.

If you have a DIN rail distribution board (e.g. ABB) and there is space you can add an RCD immediately after your existing main switch, still looks professional and is cheaper than an RCBO.

If you're confused, please post photos of your distribution board with the lid off (care please) for more focused advice.

If you are replacing your incoming breaker you need to use an RCBO to retain over-current protection.

This can be problematic (expensive) if you have one of the distribution boards using plug-in devices (e.g. Square-D) in which case a front end RCBO (Safe-T-Cut) or a DIN mount RCD (you are retaining the existing main breaker so that will provide over-current) in a simple plastic box is a cheaper, but less pro looking solution.

If you have a DIN rail distribution board (e.g. ABB) and there is space you can add an RCD immediately after your existing main switch, still looks professional and is cheaper than an RCBO.

If you're confused, please post photos of your distribution board with the lid off (care please) for more focused advice.

Is there an easy way for the layman to visually distinguish between a RCD and RCBO ?

My distribution board was a Square D model and if I recall correctly it would not have been easy to modify as the links for the live busbar to the circuit breakers seemed to be fixed in position and there was insufficient space. An external unit RCD was the alternative.

Good question steve, maybe someone else could chip in but:-

RCD - has a test button and a maximum current rating such as 30A

RCBO - has a test button and an MCB rating such as C30 (note the C denoting the MCB response curve, could be a B or D)

OR Google the part number

Some useful RCD info from UK here :http://www.esc.org.uk/public/home-electrics/rcd-faqs/

Crossy, could you please comment on this one from MK, presumably it's not suitable as it's single pole ?

http://www.screwfix.com/p/50a-30ma-sp-rcbo/51198#

The MK RCBO is intended to replace a single pole MCB in your distribution board to provide earth leakage protection to a single circuit, when it trips it does not isolate the neutral.

For front-end use you should use two pole units to provide full isolation:-

This is an RCD http://www.tlc-direct.co.uk/Products/CPR63.html

This is an RCBO http://www.tlc-direct.co.uk/Products/CPBR402.html

Scarily similar are they not

Indeed, except in pricing. At least they've marked it RCBO