TT system and RCBO's

STI

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Im trying to get my head around the CU requirements for a TT system. If i was to fit a CU with RCBO's protecting all the circuits, would the main CU switch 100A or 63A need to be a time delayed RCD or could it just be a straight forward isolator switch as the RCD protection is provided by the individual circuits RCBO's.
The current set up is 3036 rewirables with a voltage operated earth leakage type D isolator switch between the main fuse and the CU.
So would i need an RCD isolator between the main and the CU then a main switch in the CU which is a time delayed RCD then to individual circuit RCBO's.

Seems an awful lot of RCD type protection and i still have a single failure point in two places.

I am aware this is all notifiable but i am at my planning stage.
 
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If all circuits are on 30mA RCBO's, no further RCD protection is needed. The main switch provides double-pole isolation. See p. 16 OSG, Fig 2.3

Futher consideration needed if you wish to be able isolate part of the installation.
 
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If all circuits are on 30mA RCBO's, no further RCD protection is needed.
Indeed. In fact, as recently discussed here, not only is further RCD protection not required in that situation, but it is also undesirable ... a N-E fault tripping any of the (assumed single-pole) RCBOs would probably also take out an up-front RCD (even if time delayed), thereby taking out the whole installation and defeating the point of having separate protection for each final circuit.

Kind Regards, John
 
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