Why is split RCD not appropriate for TT?

[mainline]

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

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

I'm sure it says somewhere “that provision may be made for isolation of a group of circuits by a common means”

 

[swaRRR]

531.3.2 (ii)
It does say 'considered'.

The same reg also mentions split RCD though so i don't think it means RCBO's are required in residential premises.

'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.

For Class I enclosures in TT systems where RCD protection is used on outgoing circuits, double
or reinforced insulation of all live conductors (incoming cables, extension terminals, etc.) on the supply side of the
incoming device, e.g. main switch, shall be used. Insulated and non-metallic sheathed cables are deemed to meet the
requirements of double or reinforced insulation.

NOTE 1: When selecting equipment, consideration should be given to the assembly manufacturer's internal line interconnecting
cable links on the supply side of an RCD being insulated and non-metallic sheathed, or having reinforced insulation
or equivalent mechanical protection.

From the book.

Supply side of eg main switch is massively ambiguous imo.

 

[swaRRR]

I'm sure it says somewhere “that provision may be made for isolation of a group of circuits by a common means”

It doesn't, not in that quote from the OSG anyway.

 

[mainline]

It doesn't, not in that quote from the OSG anyway.

Welcome to the world of interpretation.

 

[swaRRR]

Welcome to the world of interpretation.

It's all terribly confusing.

 

[cireland]

The same reg also mentions split RCD though so i don't think it means RCBO's are required in residential premises.

For Class I enclosures in TT systems where RCD protection is used on outgoing circuits, double
or reinforced insulation of all live conductors (incoming cables, extension terminals, etc.) on the supply side of the
incoming device, e.g. main switch, shall be used. Insulated and non-metallic sheathed cables are deemed to meet the
requirements of double or reinforced insulation.

NOTE 1: When selecting equipment, consideration should be given to the assembly manufacturer's internal line interconnecting
cable links on the supply side of an RCD being insulated and non-metallic sheathed, or having reinforced insulation
or equivalent mechanical protection.

From the book.

Supply side of eg main switch is massively ambiguous imo.

You were asking about the main tails and argued that :-

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

I was merely pointing out that it does mention DI tails or reinforced insulation.

 

[mainline]

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

If that were the case would it mean that all the 1000s of consumer units that use mcbs are not compliant ?

 

[westward10]

The same reg also mentions split RCD though so i don't think it means RCBO's are required in residential premises.

For Class I enclosures in TT systems where RCD protection is used on outgoing circuits, double
or reinforced insulation of all live conductors (incoming cables, extension terminals, etc.) on the supply side of the
incoming device, e.g. main switch, shall be used. Insulated and non-metallic sheathed cables are deemed to meet the
requirements of double or reinforced insulation.

NOTE 1: When selecting equipment, consideration should be given to the assembly manufacturer's internal line interconnecting
cable links on the supply side of an RCD being insulated and non-metallic sheathed, or having reinforced insulation
or equivalent mechanical protection.

From the book.

Supply side of eg main switch is massively ambiguous imo.

It doesn't say required it suggests them.

 

[swaRRR]

You were asking about the main tails and argued that :-

I was merely pointing out that it does mention DI tails or reinforced insulation.

Nah i'm on about the load side of the main switch to the supply of the RCD's which is what the picture in OSG shows.

 

[swaRRR]

It doesn't say required it suggests them.

You said RCBO's were now required in residential installations.

 

[cireland]

It doesn't say required it suggests them.

It does say 'shall be used'.

 

[swaRRR]

It does say 'shall be used'.

It says residual current devices shall be selected to limit risk of unwanted tripping, and then goes on to list split load RCDs and RCBO's for consideration. It doesn't say RCBO's shall be used.

 

[mainline]

It does say 'shall be used'.

Regulation 531.3.2 (Unwanted Tripping) now points out the use of RCBOs for individual final circuits in residential premises as a method to prevent unwanted tripping of such protective devices.

 

[nicebutdim]

'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.

I don't believe these two statements can be reconciled.

 

[mainline]

I don't believe these two statements can be reconciled.

It makes it compliant with regard to isolation