Changing a TT system board - Best Practice

[rolyberkin]

Advice please

I have been reading through the regs re a TT system consumer unit change and the onsite guide suggests at 2.2.6 a-c that consideration should be given to the board being either be class 2 board or class 1 with RCBO's or a split board with an S Type main RCD as isolator.

The existing fuse board in question is a Wylex old style fuse board but it has a stand alone 30ma RCD on tails approx 50cm long connected between the board and the main fuse. As I see it I have two options.

1. Replace with an all RCBO board and have the up front RCD changed by the DNO for isolators (there seems to be some ongoing discussion about whether an rcbo satisfies need for both poles to be isolated) so should this type of board be fitted with an S type RCD in place of the board isolator.

2. Fit Amendment 3 split load board, changing the isolator for a time delayed two pole S type RCD.

The RCD will need to be replaced by the DNO for two isolators at some point but my consideration is I am thinking it is safer to leave the RCD as is connected to the replacement board with upgraded tails for the DNO to replace after the board has been changed, there is a discrimination issue but the tails are about 50cm max?

Any views or pointers gladly received.

 

[Leesparkykent]

why would the DNO have to install two isolators?

 

[Pete999]

What Leesparkykent said

 

[rolyberkin]

The ones that the local DNO fit are single pole isolators fitted side by side, bad description on my part.

 

[Leesparkykent]

The ones that the local DNO fit are single switches fitted side by side, bad description on my part.

That sounds dangerous...so you can isolate the neutral by itself?

 

[rolyberkin]

Can't get it right way up, this is what I meant, thought was two single isolators side by side, however now I have looked at mine it is clearly a double pole, thrown by it looking like two switches!?

 

[Pete999]

Is that a link I see between the two switches? would hazard a guess that it's a DP unit

 

[rolyberkin]

Is that a link I see between the two switches? would hazard a guess that it's a DP unit

Yep metal bar between the two, note to self, put glasses on!

 

[Leesparkykent]

call the meter operator/DNO and get them to install the switch then you can go in change the board, get rid of the 30mA RCD in the tails and put in some new tails from new board to the switch they install. If you install a dual RCD board replace the main switch in the board for a 100mA S type RCD, take the tails and main earthing conductor through a nylon tail gland to stop any abrasion with the metal casing and to support the tails. Adequately support the tails from board to new isolator using clips, trunking or the like.

 

[rolyberkin]

call the meter operator/DNO and get them to install the switch then you can go in change the board, get rid of the 30mA RCD in the tails and put in some new tails from new board to the switch they install. If you install a dual RCD board replace the main switch in the board for a 100mA S type RCD, take the tails and main earthing conductor through a nylon tail gland to stop any abrasion with the metal casing and to support the tails. Adequately support the tails from board to new isolator using clips, trunking or the like.

Thanks