4mm ring

[pete01]

If you've used 2 core and you don't earth the armour, will your new sockets have no earth, or have I missed something

 

[JohnW2]

I don't get what all the issue is about, a 4mm ring is pretty common in commericial work, and while there was probably no need to go to 4mm in the OPs case, its not wrong to do so. .... Volt drop is often the reason they are specified, but often very cautious design assumptions are made, such as assuming the loading is 20A in the middle of a ring and then extra 5A load at 1/4 and 3/4 around. When the acutal load is a couple of PCs and less than 5A...... Grouping factors are another thing that might result in 4mm rings

Indeed, you cite the two possible valid reasons for a 4mm² ring that I mentioned.

Might also be necessary to meet Zs on longer rings, espeically with C type MCBs and no RCD

As you say, that could be an issue with a C32, but I think probably pretty unlikely with a B32, since (if I've done my sums right!) Zs would then only become a problem before a "5% VD" one did if Ze were greater than about 0.72Ω, which is probably pretty unlikely in a TN installation.

Kind Regards, John

 

[JohnW2]

If you've used 2 core and you don't earth the armour, will your new sockets have no earth, or have I missed something

I think you've probably misunderstood. When he wrote ...

.... the armour!! its stripped back completely from the terminals and is not used as the earth as in 2 core.

... I took that he meant that he was using 3-core, and therefore "not using the armour as the earth as one would if it were 2-core".

Kind Regards, Joh

 

[Swwils]

Safety is the most important technical standard in BS7671.

 

[JohnW2]

Safety is the most important technical standard in BS7671.

I'm not quite sure what you mean by 'technical standard' (that's what BS7671 is) but, yes, virtually everything in BS7671 relates to 'safety', in one sense or another.

But what is your point?

Kind Regards, John

 

[russellsmiler]

is anyone happy to give me a thumbs up on what i have proposed (almost finished) ??

 

[pete01]

is anyone happy to give me a thumbs up on what i have proposed (almost finished) ??

Post a picture of the swa entering a socket

 

[pete01]

I think you've probably misunderstood. When he wrote ...

... I took that he meant that he was using 3-core, and therefore "not using the armour as the earth as one would if it were 2-core".

Kind Regards, Joh

Still need to earth the armouring regardless

 

[ebee]

Still need to earth the armouring regardless

So, let`s say I`m using three core SWA. so I have L, N & E conductors. I have used stuffing glands rather than SWA glands at the ends. Would I need to make an earthed connection to the SWA armour in every conceivable instance then ?

 

[pete01]

So, let`s say I`m using three core SWA. so I have L, N & E conductors. I have used stuffing glands rather than SWA glands at the ends. Would I need to make an earthed connection to the SWA armour in every conceivable instance then ?

I would say yes, as it's an exposed conducive part, but in the OP's case it's not going to be exposed, so bit of a grey area in my opinion

 

[JohnW2]

Still need to earth the armouring regardless

We went through this at length recently.

It certainly 'feels' like the decent thing to do, but whether it is a requirement' is a very different (and debatable) matter.

Even if SWA did not have it's armour, it would be considered safe to touch the outside of it -with no less than three layers of insulating material between live conductors and the outside. It's therefore debatable as to whether, when one adds the armour, it actually needs to be earthed.

It's really analogous to Class II items. If there are two layers of insulating material beneath it, there is no requirement for an outer metal case to be earthed (and many manufacturers say that it "MUST NOT" be earthed) - and that would be even more true if, analogous to SWA, there were yet another layer of insulating material covering the outer metal case.

As we discussed before, if one took the view that any metal in a house/building which might come into contact with the outside of an 'insulated and sheathed' cable had to be earthed, that would become pretty ridiculous (when one considered things like vacuum cleaner leads)!

Kind Regards, John

 

[EFLImpudence]

Surely it is quite clear that if the armour is being used as electrical protection (and/or as a reason not to fit an RCD) then it must be earthed.

If used only as mechanical protection, then it does not require earthing.

It is only an exposed-conductive-part if left exposed where live connections might become loose.

 

[JohnW2]

Surely it is quite clear that if the armour is being used as electrical protection (and/or as a reason not to fit an RCD) then it must be earthed. If used only as mechanical protection, then it does not require earthing.

Yes, as you will presumably realise, that is also my view. However, I can see no harm in earthing it - one doesn't even have the usual argument that 'unnecessarily' earthing something is undesirable, since the armour is not even touchable (if the cable is intact)

It is only an exposed-conductive-part if left exposed where live connections might become loose.

Well, it certainly can't be an "exposed-c-p" if it's not exposed!

However, I would be saying the same even if it were exposed (i.e. if the armour were outside all three layers of insulating materia), and I don't think that would qualify as an exposed-c-p (per BS7671 definition) - since that definition not only requires that it can be touched, by also that it "..... is not normally live, but which can become live under fault conditions" - since it could only become life if there were simultaneous faulkts of all three layers of insulating material. That's much the same as an outer metal casing of a Class II item not qualifying as an exposed-c-p (which needs earthing).

Kind Regards, John

 

[EFLImpudence]

Agreed - but you seem to be counter arguing "if left exposed where live connections might become loose" with examples of "exposed or not exposed with no connections likely to become loose".

 

[JohnW2]

Agreed - but you seem to be counter arguing "if left exposed where live connections might become loose" with examples of "exposed or not exposed with no connections likely to become loose".

I'm not sure I understand. I have not said anything about (nor even considered to much of an extent) anything 'becoming loose'.

Let's face it, 'connections becoming loose' anywhere in an electrical installation can cause problems, and I'm not sure what that has got to do with our discussion about the earthing (or not) of 'unused' SWA armour.

Can you perhaps clarify?

Kind Regards,
John