Why is split RCD not appropriate for TT?

[westward10]

Regulations now require residential to be rcbos.

 

[westward10]

No, but this seems to be a regular occurrence where the OSG says something and it turns out it's not actually a reg. Is the OSG fit for purpose?

Not looked at an OSG for over 20 years your book of choice is BS7671.

 

[cireland]

Does the OSG cite a Regulation.

Wouldn't it be covered by the same regulations stating TT systems have to be RCD protected. This wiring is still on the consumer side of the main switch albeit within the consumer unit itself.

 

[swaRRR]

Not looked at an OSG for over 20 years your book of choice is BS7671.

I know that but OSG is supposed to be a bite-sized, easy reference for whats in the big brown book. Seems like the OSG talks a lot of gibberish.

Here's another one.

OSG page 61.

'Other than at the origin of the installation, every circuit...that may have to be isolated without interrupting the supply to other circuits should be provided with its own isolating device. The device must switch all live conductors in a TT system and all line conductors in a TN system.'

This basically says all breakers have to be double pole in a TT, no?

Yet you go to 132.15.201 which the OSG references and it says absolutely nothing about this.

 

[mainline]

No, but this seems to be a regular occurrence where the OSG says something and it turns out it's not actually a reg. Is the OSG fit for purpose?

Think it stems from
Regulation 531.3.5.3.2.201

 

[JBW175]

No spark worth his salt is fitting split load boards these days IMO.

RCBO & SP is all I quote for.

 

[mainline]

I know that but OSG is supposed to be a bite-sized, easy reference for whats in the big brown book. Seems like the OSG talks a lot of gibberish.

Here's another one.

OSG page 61.

'Other than at the origin of the installation, every circuit...that may have to be isolated without interrupting the supply to other circuits should be provided with its own isolating device. The device must switch all live conductors in a TT system and all line conductors in a TN system.'

This basically says all breakers have to be double pole in a TT, no?

Yet you go to 132.15.201 which the OSG references and it says absolutely nothing about this.

The DP main switch makes it compliant.

 

[swaRRR]

Regulations now require residential to be rcbos.

Which reg is that?

 

[swaRRR]

The DP main switch makes it compliant.

That quote though says that all individual circuits must have their own DP isolating device. Yet the regs don't mention it.

 

[cireland]

The DP main switch makes it compliant.

It does mention 'without interrupting the supply to other circuits'.

 

[swaRRR]

Think it stems from
Regulation 531.3.5.3.2.201

But that reg says supply side of the incoming device eg main switch. **** me these books are confusing. Someone should rewrite them in normal language, they'd make millions.

 

[cireland]

But that reg says supply side of the incoming device eg main switch. **** me these books are confusing. Someone should rewrite them in normal language, they'd make millions.

It does also mention the internal wiring I think. Says something about them being double insulated or
reinforced.

 

[swaRRR]

It does also mention the internal wiring I think. Says something about them being double insulated or
reinforced.

Only as it pertains to a pre-assembled board's link cables as far as i can see.

 

[westward10]

Which reg is that?

531.3.2 (ii)
It does say 'considered'.

 

[cireland]

Only as it pertains to a pre-assembled board's link cables as far as i can see.

'Regulation 531.3.5.3.2.201 requires that where Class I enclosures are installed in installations forming part of a TT system and RCD protection is used on outgoing circuits, all live conductors on the supply side of the incoming device must have double or reinforced insulation'.

Taken from NICEIC website.