Ring Final Circuit wired in 4 core SWA

[SoulTy1066]

Hi Gents,

Have an existing circuit at a warehouse where a single 4mm 4core SWA has been used as a Ring Final Circuit. Two cores are in connectors in the back of the socket outlets thus creating a ring. The SWA is therefore the sole means of earthing. There are No banjo's at the sockets and the glands are screwed into galv couplers at the sockets too.
All opinions welcome..

 

[Leesparkykent]

metal clad socket/boxes with fly lead?

 

[Wilko]

Can I ask please what is the mcb type and rating, and the installation method?
I can't picture how the armour gets to the socket earth, but it is Friday ...

 

[Pete999]

Can I ask please what is the mcb type and rating, and the installation method?
I can't picture how the armour gets to the socket earth, but it is Friday ...

Piranha earth lock nut behind the brass bush + fly lead = difficult I know but it could be done.

 

[Wilko]

The RFC is already a bit of a thing and this is a complication of it. I was going to spell that with a b... but refrained ... As the RFC relies on distributed loads that could be a problem (?). Maybe that could be simulated by alternating outlets across the pairs (if that makes any sense). Then there's the cpc aspect. Armour is fine for that in theory, but will depend on the mcb and Zs.

 

[westward10]

Only problem I see here is no cpcs from the cable glands to the socket earth terminal. Couplers would need removing and gland direct to back box then fit earth washers or earthing nuts.

 

[Richard Burns]

If these are metal clad sockets and the SWA gland is fixed to the galvanised coupler and the coupler is securely fixed to the metal of the back box, then the back box would be acting as the continuation for the cpc across the socket. The connection to the socket earth would be via the metal back box and the accessory screws and any continuity from the contact of the face plate to the back box.

I do not know the current carrying capacity of a metal back box or the security of earthing for the accessory screws (though it seems acceptable for plastic fittings to earth a flush back box) but I would feel that this is not sufficient certainty of current carrying capacity for the earth, even if the continuity is good.

I would prefer fly leads from the armour connection to the socket terminals.

 

[westward10]

If the socket has a threaded entry I would agree, cpc from back box to front plate. But it doesn't.

 

[The Ghost]

Ah its ok the earth will be achieved by the front cover screws!

 

[Octopus]

Two cores are in connectors in the back of the socket outlets thus creating a ring.

Is it me or what is this suggesting?

 

[Deleted member 26818]

If this was conduit instead of SWA, would banjos be required?

 

[Richard Burns]

Is it me or what is this suggesting?

Not very clear is it, a core would indicate line or neutral, but it might mean a fly lead.

If this was conduit instead of SWA, would banjos be required?

I would still like fly leads at least from back box to socket terminal if not to the conduit/gland.

 

[The Ghost]

As I understand it, four cores, two to each socket, two to return the ring. (Bit like Hobbit talk) So at last socket the two joined in each socket return to origin, yes?

 

[westward10]

It must be two four cores with the return cores probably at block connectors.

 

[Pete999]

Is it me or what is this suggesting?

It means RFC wired in 4 core cable 4 cores to 1st socket 1 pair connected to anothe pair going to the next socket until you reach the last one where you have 2 L and 2 N, ergo a RFC wired in 4 core.

 

[Wilko]

One ring to rule them all ... perhaps JRRT was a spark?

 

[Pete999]

One ring to rule them all ... perhaps JRRT was a spark?

Go on JRRT?

 

[SoulTy1066]

The RFC is already a bit of a thing and this is a complication of it. I was going to spell that with a b... but refrained ... As the RFC relies on distributed loads that could be a problem (?). Maybe that could be simulated by alternating outlets across the pairs (if that makes any sense). Then there's the cpc aspect. Armour is fine for that in theory, but will depend on the mcb and Zs.

Type C 32amp RCBO with Zs of 0.72 so over on Max Zs.

 

[SoulTy1066]

It means RFC wired in 4 core cable 4 cores to 1st socket 1 pair connected to anothe pair going to the next socket until you reach the last one where you have 2 L and 2 N, ergo a RFC wired in 4 core.

You've got it... If it had been glanded straight into the metalclad sockets and used piranha nuts it would of been better.

 

[westward10]

Type C 32amp RCBO with Zs of 0.72 so over on Max Zs.

Maybe poor circuit design but the rcbo will provide fault protection.

 

[Pete999]

You've got it... If it had been glanded straight into the metalclad sockets and used piranha nuts it would of been better.

When you look at this type of system in the cold light of day regarding the earthing/cpc and ignore the L and N conductors the and the Armour being suitable for use as a cpc, then there isn't much difference from that to a metal conduit install. You don't run a cpc in metallic conduit you fly lead from the earth stud in the box to the earth terminal on the socket face plate, no difference in doing the same with the SWA install is there?

 

[HandySparks]

Go on JRRT?

J. R. R. Tolkien - Wikipedia - https://en.wikipedia.org/wiki/J._R._R._Tolkien

 

[Des 56]

If this was a standard 4mm radial without the addition of an extra help for the live and neutral (in the form of another 2 cores to assist) maybe the collective eyebrows would not be so lifted

 

[westward10]

If this was a standard 4mm radial without the addition of an extra help for the live and neutral (in the form of another 2 cores to assist) maybe the collective eyebrows would not be so lifted

Wash your mouth out it is a 13A socket and MUST be a ring final

 

[Des 56]

Wash your mouth out it is a 13A socket and MUST be a ring final

Prefer to stand at the back of the class

 

[mickfred]

Never uses two core swa for sockets, but when i use metal clad socket ( am waiting to hear "why") but i alway take the paint off in the inside round the knockout (it reassure me)

 

[Deleted member 26818]

So let me get this straight.
If we install conduit, we don't need banjos or piranha nuts, but if we use SWA, we do?

 

[Wilko]

Maybe poor circuit design but the rcbo will provide fault protection.

I think 32B would fit better, and for clarity I'm talking about mcb not items of clothing ...

 

[PEG]

I'm loving this threads tombola randomness

 

[Pete999]

Never uses two core swa for sockets, but when i use metal clad socket ( am waiting to hear "why") but i alway take the paint off in the inside round the knockout (it reassure me)

Should be done on ALL metal enclosures, where conduit or SWA installations, lost count of the number of hours I spent filing coupler ends flat, filing lock nuts, cleaning paint from enclosures, not for reassurance, but for a good contact, a lost practice these days I'm afraid.

 

[westward10]

When I started out I was told to thread the conduit and use two lock nuts tightened up on to themselves and a female bush on the inside, must admit not done that for years.

 

[Pete999]

When I started out I was told to thread the conduit and use two lock nuts tightened up on to themselves and a female bush on the inside, must admit not done that for years.

All sorts of ways of doing things back in the good old days Westy

 

[Toneyz]

All sorts of ways of doing things back in the good old days Westy

I bet you if you put the fittings of today eg couplers bushed glands etc. against ones from past side by side you would notice a huge difference.

 

[SoulTy1066]

More worried about using a single 4 core as a ring

 

[Pete999]

More worried about using a single 4 core as a ring

Used to be the norm with 4 core MICC/SWA, of course they don't teach that sort of thing nowadays, shame really.