TT With Amd 3 boards

S

soulman

-
Arms
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
 
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soulman said:
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
Click to expand...

It's not the advice I received from Elecsa Technical. A3 Dual CU's with a TT supply will require S Type for the reason you've given, either as a main switch, or as a stand alone.
 
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Soulman, how was this advice obtained?

I very rarely now make contact with technical via phone, always by email. I find you get a more considered and in depth response that way, with specific regulations referred to (not specific, in this case). I think via phone, they are sometimes too quick to finish the call, and your question can get 'lost in translation'.
 
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soulman said:
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
Click to expand...
If it's a dual rcd consumer unit the tails should enter the metal enclosure through a insulated stuffing gland to protect against abrasions of the tails.
I would install an s type 100mA rcd as the main switch to protect the tail links inside the consumer unit which if become loose and short out on to the casing and becomes a dangerous situation. technically the tails and links will need a 1 second disconnection time so the s type will give you this.
 
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Hi, Thanks for replies,
Yes it was via telephone. They said that as a long as a stuffing gland is used for the tails (Which would always be used) the manufacturers have designed unit for all situations. I explained in detail that I have given a code 2 observation for this during a periodic. My personal take on it is, the on site guide recommends the use of an rcd to protect the conductors from the main switch to the rcd's as they only have insulation & no sheath. Therefore in my opinion it is unlikely to happen, but still has the potential to happen & cause a dangerous situation, therefore I will continue to use a RCD as the main switch. I did ask Elecsa when AMD 3 boards come into play, if I could use a REC2 Enclosure before the board with a 100ma S type. They said no as the REC2 enclosures are plastic. Which to me is crazy as this would also protect the tails entering the board.
 
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soulman said:
Hi, Thanks for replies,
Yes it was via telephone. They said that as a long as a stuffing gland is used for the tails (Which would always be used) the manufacturers have designed unit for all situations. I explained in detail that I have given a code 2 observation for this during a periodic. My personal take on it is, the on site guide recommends the use of an rcd to protect the conductors from the main switch to the rcd's as they only have insulation & no sheath. Therefore in my opinion it is unlikely to happen, but still has the potential to happen & cause a dangerous situation, therefore I will continue to use a RCD as the main switch. I did ask Elecsa when AMD 3 boards come into play, if I could use a REC2 Enclosure before the board with a 100ma S type. They said no as the REC2 enclosures are plastic. Which to me is crazy as this would also protect the tails entering the board.
Click to expand...
But if you fit plastic enclosure switchgear it defeats the object of a non combustible DB.......The RCD enclosure would now be the 'fire hazard'.
 
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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.
 
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freddo said:
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.
Click to expand...
What is a non standard domestic install:D
 
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Ian1981 said:
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.
Click to expand...
Main switch in a CU, 60947-3. Main switch for one of those DNO things 60947-3.
 
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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 ! :)
 
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Murdoch said:
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.
Click to expand...
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
 
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soulman

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TT With Amd 3 boards
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