I want to install an under sink Water Heater, so need to fit 40amp RCD to a Proteus Fuse box, is it just the Mains switch I isolate as I can not access anything else that has not been sealed. 
Adding RCD to Main Fuse box
- Thread starter davewellings
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You mean a 40A RCBO? If so then yes just isolate the main switch. If you mean install an RCD for the whole board then this would not be compliant, and you'll struggle if you're replacing the main switch for an RCD as the tails will still be live.
Some pictures might help.
Some pictures might help.
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Theory and practice are two different things. In theory before working on any board you should isolate elsewhere. On large commercial boards I have heard of electricians being fined by HSE for not complying with this. In practice we often take a chance and isolate at the consumer unit as the only way to comply with HSE requirements in many cases would be to draw the supply authorities fuse.
Because of the dangers of working in a live board the Part P regulations require one to notify the LABC for work inside the consumer unit. This then gets expensive one because of LABC charges and secondly as you need to supply test figures which in turn mean hiring of test equipment at around another £75.
So in practice I know many do not test or inform the LABC but this can invalidate insurance and cause problems when selling the house.
So for an under sink heater does it need over 13A. The ones I have fitted could have 5A or 13A elements and stored 7 litres of water. These did not really need wiring all the way back to the consumer unit.
If 13A is enough then you have 3 options without going to consumer unit.
RCD FCU
RCD Socket
RCD Plug
The only disadvantage is they will be active so after a power cut will need resetting.
In the consumer unit if over 13A then there are again 3 options.
RCBO which is a RCD and MCB combined these are easy to fit.
RCD in consumer unit. Likely will mean consumer unit change see below.
External box with either RCD or RCBO fitted.
The problem is:- 314.1 Every installation shall be divided into circuits, as necessary, to:
(iii) take account of danger that may arise from the failure of a single circuit such as a lighting circuit
(iv) reduce the possibility of unwanted tripping of RCDs due to excessive protective conductor currents produced by equipment in normal operation
This in most cases means you can't use a single RCD.
The other problem is earthing type with a TN system there is not a problem but with a TT system then all pole switching is required on the RCD which is a problem when using British consumer units with RCBO's as they are single pole.
In other words once you go inside the consumer unit you really do need to know what you are doing.
Not worked on Mon so don't know type of supply. But I would say only go into consumer unit if there is no other method of fitting a RCD. And I would consider worth the few extra bob to get an electrician to do the work and be sure it all complies with regulations.
Because of the dangers of working in a live board the Part P regulations require one to notify the LABC for work inside the consumer unit. This then gets expensive one because of LABC charges and secondly as you need to supply test figures which in turn mean hiring of test equipment at around another £75.
So in practice I know many do not test or inform the LABC but this can invalidate insurance and cause problems when selling the house.
So for an under sink heater does it need over 13A. The ones I have fitted could have 5A or 13A elements and stored 7 litres of water. These did not really need wiring all the way back to the consumer unit.
If 13A is enough then you have 3 options without going to consumer unit.
RCD FCU
RCD Socket
RCD Plug
The only disadvantage is they will be active so after a power cut will need resetting.
In the consumer unit if over 13A then there are again 3 options.
RCBO which is a RCD and MCB combined these are easy to fit.
RCD in consumer unit. Likely will mean consumer unit change see below.
External box with either RCD or RCBO fitted.
The problem is:- 314.1 Every installation shall be divided into circuits, as necessary, to:
(iii) take account of danger that may arise from the failure of a single circuit such as a lighting circuit
(iv) reduce the possibility of unwanted tripping of RCDs due to excessive protective conductor currents produced by equipment in normal operation
This in most cases means you can't use a single RCD.
The other problem is earthing type with a TN system there is not a problem but with a TT system then all pole switching is required on the RCD which is a problem when using British consumer units with RCBO's as they are single pole.
In other words once you go inside the consumer unit you really do need to know what you are doing.
Not worked on Mon so don't know type of supply. But I would say only go into consumer unit if there is no other method of fitting a RCD. And I would consider worth the few extra bob to get an electrician to do the work and be sure it all complies with regulations.
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Not if you use a passive one:
http://www.screwfix.com/p/13a-30ma-double-pole-passive-twin-socket-rcd/83453
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