TT With Amd 3 boards

[soulman]

Hi, when installing a consumer unit in domestic premises, I have been swopping out the main switch for an S type 100ma rcd. The reason I have been doing this is advice given in the on-site guide. PG 34 & 35. Dual RCD boards : Stating that there is insufficient fault protection of the single insulated conductors from the bottom of the main switch to the top of the rcd's.
I have come across a few installs recently (TT) that don't have a rcd main switch, I queried this with the Technical Helpline & they state I don't need one.
Does anyone else install a RCD main switch.

Cheers

 

[Ian1981]

I personally wouldn't class the electricity distributors isolator as "similar switchgear" to that of a consumer unit.

 

[freddo]

For TT the OSG suggests an insulating gland and a 100mA time delay RCD main switch if a dual RCD board is used due to the single insulation on the internal tails to the RCDs. If an all RCBO board is used the time delay RCD can be omitted. For a standard domestic install, single pole RCBOs are fine.

 

[westward10]

I personally wouldn't class the electricity distributors isolator as "similar switchgear" to that of a consumer unit.

I would.

 

[Ian1981]

I would.

Fair enough.
I'd say it's just an isolation point and doesn't contain similar switch gear assembly's as a consumer unit would circuit breakers,fuses etc.
That's my take on it anyway.

 

[westward10]

For TT the OSG suggests an insulating gland and a 100mA time delay RCD main switch if a dual RCD board is used due to the single insulation on the internal tails to the RCDs. If an all RCBO board is used the time delay RCD can be omitted. For a standard domestic install, single pole RCBOs are fine.

What is a non standard domestic install

 

[westward10]

Fair enough.
I'd say it's just an isolation point and doesn't contain similar switch gear assembly's as a consumer unit would circuit breakers,fuses etc.
That's my take on it anyway.

Main switch in a CU, 60947-3. Main switch for one of those DNO things 60947-3.

 

[freddo]

What is a non standard domestic install

A house that has its own marina?!

 

[Ian1981]

Main switch in a CU, 60947-3. Main switch for one of those DNO things 60947-3.

It's the similar switch gear assembly I take as being the same not a switch on its own.
Would you code this in a eicr or note it maybes?
It's an interesting take on it as the DNO have their own regs as it where so just curious

 

[Dave OCD]

If there's a risk of an internal non-protected factory cable link coming adrift within a CU and making the enclosure live then there has to be at least an equal risk of the meter tails escaping from the main incomer and causing the same problem ? So the only way to be sure of dealing with these scenarios safely is to have an external S type RCD, I'd happily fit that in an insulated enclosure. Although realistically with proper workmanship neither will ever happen- Ah therein may lie the problem !

 

[freddo]

It's more to do with the internal wiring being single insulated and the risk of insulation damage rather than the wires falling out of the terminals.

 

[Octopus]

I suppose the basic question is "is a switched fuse" considered the same as a fuse board?

Tin hat on.

 

[Ian1981]

It's more to do with the internal wiring being single insulated and the risk of insulation damage rather than the wires falling out of the terminals.

Or possibly both

 

[Dave OCD]

Good point but there's no movement in there to cause abrasion and to damage the insulation on those links would require a high degree of idiocy.

 

[Ian1981]

I suppose the basic question is "is a switched fuse" considered the same as a fuse board?
I would say yes as it has similar switch gear i.e. A fuse with outgoing circuit ,main switch isolation double pole.

I would say yes as it has similar switch gear assemblies i.e. A fuse protecting an outgoing circuit and a double pole isolation mains switch

 

[plantpot]

If only the manufacturers would make sheathed links in the board this would be solved