Wylex 100A dp isolators in plastic enclosures.

John Peckham:

Metal enclosures do not need to be replaced if the cable sheath is left on the tails all the way up to the main switch and the tails enter through a plastic gland with a rubber insert so 4 layers of insulation. Whiska and other manufacturers make glands for this situation.

Posted by whjohnson on Sep 28, 2019 6:19 pm

The 16mm tails are indeed sheathed all the way into the enclosure, and a standard CTS gland rather than a dedicated tails one

In the absence of terminals for CPCs, the single RCD isolator cannot be a distribution board.

Chris Pearson:

gkenyon:

AJJewsbury:

but the RCD would almost certainly make it "similar switchgear"

I'd still argue not - without any overcurrent protective devices there's no incoming or outgoing circuits - it's all (by the definition of a circuit) all one circuit. It can't therefore be a distribution board, and thus not any particular type of distribution board that is a consumer unit, so any similarity doesn't seem at all obvious. Let alone meeting the switchgear definition's requirement for containing both main and auxiliary switching equipment.


  - Andy

Well, this is where it gets tenuous.


The overcurrent protection may be downstream of the device (in this case usually justifiably so), therefore it fits into the "one or more fuses, circuit breakers, residual current operated devices" category in the definition of Consumer Unit in BS 7671. Certainly, the single RCD-isolator controls energy, and is certainly involved in the distribution of electrical energy.

I do not think that it is tenuous at all.


Definition of consumer unit: A particular type of distribution board ... So if the single RCD isolator is not a distribution board, it cannot be a consumer unit.


I have no doubt that the inclusion of a single circuit does not prevent something from being a DB. After all, an installation could be made in stages with only one circuit initially.


Definition of distribution board: An assembly containing switching or protective devices ... together with terminals for the neutral and circuit protective conductors. In the absence of terminals for CPCs, the single RCD isolator cannot be a distribution board.


QED.

 

gkenyon:

Chris Pearson:

gkenyon:

AJJewsbury:

but the RCD would almost certainly make it "similar switchgear"

I'd still argue not - without any overcurrent protective devices there's no incoming or outgoing circuits - it's all (by the definition of a circuit) all one circuit. It can't therefore be a distribution board, and thus not any particular type of distribution board that is a consumer unit, so any similarity doesn't seem at all obvious. Let alone meeting the switchgear definition's requirement for containing both main and auxiliary switching equipment.


  - Andy

Well, this is where it gets tenuous.


The overcurrent protection may be downstream of the device (in this case usually justifiably so), therefore it fits into the "one or more fuses, circuit breakers, residual current operated devices" category in the definition of Consumer Unit in BS 7671. Certainly, the single RCD-isolator controls energy, and is certainly involved in the distribution of electrical energy.

I do not think that it is tenuous at all.


Definition of consumer unit: A particular type of distribution board ... So if the single RCD isolator is not a distribution board, it cannot be a consumer unit.


I have no doubt that the inclusion of a single circuit does not prevent something from being a DB. After all, an installation could be made in stages with only one circuit initially.


Definition of distribution board: An assembly containing switching or protective devices ... together with terminals for the neutral and circuit protective conductors. In the absence of terminals for CPCs, the single RCD isolator cannot be a distribution board.


QED.

 

Where ADS is used, a cpc has to be run and terminated at each point in wiring (Reg 411.3.1.1).

So, if you provide the RCD because it's TT, you provide a CPC ... and terminate it ...

 

Alcomax:

 

Did you really believe that? 



It is TT.   411.3.1.1, 1st paragraph:  "EPC shall be connected  to a protective conductor under the specific conditions for each type of earthing system as spec'd in regs 411.4 to 411.6, of which one is TT.

Where ADS is used, a cpc has to be run and terminated at each point in wiring (Reg 411.3.1.1).

Is a selective quote from the last paragraph of the reg  

So, if you provide the RCD because it's TT, you provide a CPC ... and terminate it ...

Not so if that equipment does not need one because it is class II.    It should, or would, not be altered by anyone else [an ordinary person] to a class 1 enclosure unless the earthing system was changed to TN or the person doing the alteration decided to take advantage of 531.3.5.3.2.201 and have a class 1 [ steel ] enclosure for the upfront RCD and make a claim on the tails being double or reinforced insulation.

 

412.1.2  is quite specific that the protective measure of double or reinforced insulation is not to be applied where any part has an earthing contact

I think with all that in mind, an upfront outboard RCD in a metal box is by far the worst way to go on a TT earthing system.

I think with all that in mind, an upfront outboard RCD in a metal box is by far the worst way to go on a TT earthing system.

Agree, with a note that a switch in a metal box feeding a selection of non RCS protected bus bar or split tails to many RCDs is much worse than an RCD in a smaller metal box with only tails in and out and nothing else.

It would be safer with an un-earthed metal box, and some more insulation inside.

The safest solution by far is an RCD on its own in a plastic box, tails in and out and no electrode only CPC anywhere near it.

The regs in their current form can be read in a way that seems to recommend some  highly suspect practice.

 

mapj1:

I think with all that in mind, an upfront outboard RCD in a metal box is by far the worst way to go on a TT earthing system.

Agree, with a note that a switch in a metal box feeding a selection of non RCS protected bus bar or split tails to many RCDs is much worse than an RCD in a smaller metal box with only tails in and out and nothing else.

It would be safer with an un-earthed metal box, and some more insulation inside.

The safest solution by far is an RCD on its own in a plastic box, tails in and out and no electrode only CPC anywhere near it.

The regs in their current form can be read in a way that seems to recommend some  highly suspect practice.