SWA armour connection in metal distribution board.

[JACKC]

Hi,
What is the standard for connecting the armour on a metal dissy board. Main incomer is 25mm 5 core with banjo at both ends and 1 core used as earth. Understand that it is best to do this. Now have 6 circuits from the board going to 32 amp and 16 amp 3 phase sockets. The armour on these has not been linked from the banjo to earth as again a core has been used for the earth. Just wondered why this is so as not much experience of swa requirements. Socket end is on a plastic enclosure and is earth fly lead from banjo. TIA to anyone who posts.

 

[Spark123]

Yes, you still need to connect the banjo to the correct earth terminal using suitable sized cable.
//www.diynot.com/wiki/electrics:swa-gland

 

[ericmark]

You need to use some common sense. If the box is painted and has gaskets on the gland plate then you need an earth wire. And of course that earth wire needs to be able to take the fault current so 4mm earth wires on 25mm cables is no good.
However there are times where only the supply end of the cable has the armour connected to earth. In the main to reduce EMC problems.
But of course the out going cables from your box will need the armour bonding to earth and it is often easier to bond incoming gland to outgoing gland then take an earth from the earth core.
At the end of the day the armour is steel and you are connecting this to brass, and the box in diagram is steel and being bolted to the brass gland and it is highly unlikely that the steel box will not bond the earth. Same goes for where tray work is bolted together I can see no point in little cables from one bit of tray to the other. This would only be required when clipped together.
Correct method with tray is a copper earth cable with tails coming off it to earth each piece of tray with

these.
Same with box correct method is to bond to copper core so each piece of steel is earthed by copper. However this may be correct method but rarely done except in petro-chemical installations.

 

[ban-all-sheds]

Yes, you still need to connect the banjo to the correct earth terminal using suitable sized cable.
//www.diynot.com/wiki/electrics:swa-gland[/QUOTE]
How do we know that the final circuits actually need to have earthed mechanical protection?

 

[Spark123]

It is SWA, the CPC in SWA being the armour.

 

[ricicle]

It is SWA, the CPC in SWA being the armour.

The armour on these has not been linked from the banjo to earth as again a core has been used for the earth.

It appears that the armour is not being used as a CPC. I would still earth the armouring correctly at the mains end anyway to afford earthed mech. protection as it is SWA.

 

[Spark123]

The armour is still the CPC wether or not a conductor meant for use as a live conductor is being used as the CPC connection for downstream equipment or not.

 

[ricicle]

The armour is still the CPC wether or not a conductor meant for use as a live conductor is being used as the CPC connection for downstream equipment or not.

I disagree - unless you mean it will be in parallel anyway with the intended CPC (ie the internal core)

 

[ban-all-sheds]

The armour is still the CPC wether or not a conductor meant for use as a live conductor is being used as the CPC connection for downstream equipment or not.

It can't be the CPC if it's not connected as such.

 

[Spark123]

In SWA is the armour is the circuit protective conductor, similar concept to twin and earth where the bare core is the CPC.
The fact that someone has provided an extra core for use as a CPC such as using a 3 phase cable for single phase doesn't get away from that.
I have never installed a SWA without the armour connected to the CPC regardless of wether there is an extra core doubled up with the armour.

 

[ban-all-sheds]

In SWA is the armour is the circuit protective conductor, similar concept to twin and earth where the bare core is the CPC.

No core or other conductor can "be" a cpc if it isn't connected as such.

Never seen twin&earth used to supply a timed fan, or as a strapper in 2-way switching? It doesn't matter how wrong or dangerous it is, the fact is that it is sometimes done, and when it is it is ludicrous to say that the bare core IS the cpc.

And if you've got 3-core & earth, but only need 1 phase & 1 neutral, is there a regulation which makes it compulsory to use the bare core as the cpc and/or forbids the use of one of the other cores, properly identified at the terminations?

The fact that someone has provided an extra core for use as a CPC such as using a 3 phase cable for single phase doesn't get away from that.

Are you saying that it is compulsory to use the armour as the cpc?

What if the designer/installer wishes to follow the route of 543.1.4, and the armour is too small?

Why are some SWA cables made with a green/yellow core?

I have never installed a SWA without the armour connected to the CPC regardless of wether there is an extra core doubled up with the armour.

That's not the point - the point is do you have to?

 

[ColJack]

if it doesn't fulfill the requirements of the adiabatic, you still need to earth the armour for protection of the cable, otherwise why bother to use SWA in the first place?

 

[JACKC]

Thanks for all of the replies, sparky friend has told me as all posts on here have that their is no requirement in the regs to do it but it is what he was taught to do even if another core is used as and identified as the cpc. Some sizes of swa do not meet requirements of the adiabatic equation and a seperate earth must be used to satisfy, so using the spare core in the swa is acceptable. Thanks for all of your help. Fly lead should be used to fulfil the earthed mechanical protection in his mind.

 

[ban-all-sheds]

if it doesn't fulfill the requirements of the adiabatic, you still need to earth the armour for protection of the cable, otherwise why bother to use SWA in the first place?

Because usually you do need earthed mechanical protection if you're using SWA. Otherwise you wouldn't use it.

But I'm sure there must be times when someone who's lazy and doesn't have to pay for the materials has used SWA just because it was there.

 

[Spark123]

In SWA is the armour is the circuit protective conductor, similar concept to twin and earth where the bare core is the CPC.

No core or other conductor can "be" a cpc if it isn't connected as such.

Never seen twin&earth used to supply a timed fan, or as a strapper in 2-way switching? It doesn't matter how wrong or dangerous it is, the fact is that it is sometimes done, and when it is it is ludicrous to say that the bare core IS the cpc.

Yes, I have seen it incorrectly used. No person that calls themselves an electrician will ever use the bare core for anything other than a CPC. You are correct in that unless it is connected correctly that it isn't a CPC however that is up to the sparky doing the job to correctly do that. The bare core in a twin and earth must only ever be used as a CPC.

And if you've got 3-core & earth, but only need 1 phase & 1 neutral, is there a regulation which makes it compulsory to use the bare core as the cpc and/or forbids the use of one of the other cores, properly identified at the terminations?

Not sure on there being a regulation however it has always been taught that way - call it good workmanship if you like. Similarly it wouldn't be a good idea to leave a bare core not connected to earth anyway as it can float up to near mains potential via capacitive coupling.

The fact that someone has provided an extra core for use as a CPC such as using a 3 phase cable for single phase doesn't get away from that.

Are you saying that it is compulsory to use the armour as the cpc?

Sort of, you may use the additional core as "the" CPC however the armour is intended to be connected to the protective conductor as an exposed conductive part would be.

What if the designer/installer wishes to follow the route of 543.1.4, and the armour is too small?

Then he is stuffed, just as he would be trying to use 543.1.4 with twin and earth really.

Why are some SWA cables made with a green/yellow core?

Not seen it myself, but I'd imagine you can order a cable full of white cores if you so wish too. Maybe so it can be doubled up with the armour to comply with 543.1.4 or depending on the other factors to ensure the cable is large enough for use as a bonding conductor etc.

I have never installed a SWA without the armour connected to the CPC regardless of wether there is an extra core doubled up with the armour.

That's not the point - the point is do you have to?

Yes - I would say we do. I also seem to remember that the part of a SWA doesn't constitute a sheathed cable hence there is insufficient insulation to not have the armour earthed.