Sub Main and seperate earth

[South Spark]

If I'm running two core 25mm SWA as the submain with a 16mm (non-armoured) earth seperately then will the earth require its own mechanical protection?

Also as regards earthing the armour wire - will 6mm (from the tag to the earth block) be sufficient as it now counts as extraneous metalwork?

 

[D Skelton]

Why aren't you using the armour as the earth?

 

[Knobhead]

The armours alone are more than ample. Just use a short amount of you’re 10mm for each end of the armours and save the rest for the next job.

Waste of money.

 

[plugsandsparks]

I generally use armourings if i am designing BUT i have come across two industrial sites and at least one main contracting company that thought i was some kind of lunatic for suggesting such a think. Where earth is run alongside the supply SWA it needs to follow same route, easiest is to tie wrap it to the supply cable. Mechanical protection not mandatory but make a judgement call on the environment.

 

[D Skelton]

Also, with regards to the armour of the SWA, if you intend not to use this as an earthing conductor (not sure why you would do this unless the DNO has specifically stated no exporting of their PME) if this is terminated correctly at both ends then the armour is neither an exposed or an extraneous conductive part and as such does not 'need' earthing or bonding although highly preferable, but, if you intend for it to be buried in the ground it will need earthing (ideally at the supply end) as per 522.6.100 and if you intend for it to be buried in a wall at a depth of less than 50mm then it will need earthing as per 522.8.10. Carrying out an adiabatic equation will confirm the size of the CPC needed to earth the armour.

 

[44ALLAN]

Also, with regards to the armour of the SWA, if you intend not to use this as an earthing conductor (not sure why you would do this unless the DNO has specifically stated no exporting of their PME) if this is terminated correctly at both ends then the armour is neither an exposed or an extraneous conductive part and as such does not 'need' earthing or bonding although highly preferable, but, if you intend for it to be buried in the ground it will need earthing (ideally at the supply end) as per 522.6.100 and if you intend for it to be buried in a wall at a depth of less than 50mm then it will need earthing as per 522.8.10. Carrying out an adiabatic equation will confirm the size of the CPC needed to earth the armour.

(if this is terminated correctly at both ends then the armour is neither an exposed or an extraneous conductive part and as such does not 'need' earthing or bonding ).

Hi mate....... I'm a bit confused with the above statement.
Are you saying that because the Swa has an outer sheath and will be shrouded at both ends then it negates the necessity to earth it?
I'm always willing to learn but would have thought it was always an exposed conductive part and would need earthing ( which it would be if it was terminated correctly at both ends surely?).
An internal /external cable fault would need the armour to be earthed would it not?
Sorry if I'm having a 'blonde moment' lol

 

[Engineer54]

The only reason i can see for using a separate earthing/bonding conductor is if your extending a PME system outside of it's home equipotential zone, (eg, where extraneous services etc are going to be present) as the SWA will not comply with bonding CSA. But in that case, i would useing a 3 core SWA cable, the cost will be off-set by the time it's going to take you fluffing about running a separate 16mm single earthing/bonding conductor and tying it to the SWA cable!!

 

[D Skelton]

(if this is terminated correctly at both ends then the armour is neither an exposed or an extraneous conductive part and as such does not 'need' earthing or bonding ).

Hi mate....... I'm a bit confused with the above statement.
Are you saying that because the Swa has an outer sheath and will be shrouded at both ends then it negates the necessity to earth it?
I'm always willing to learn but would have thought it was always an exposed conductive part and would need earthing ( which it would be if it was terminated correctly at both ends surely?).
An internal /external cable fault would need the armour to be earthed would it not?
Sorry if I'm having a 'blonde moment' lol

It is possible to terminate SWA in compliance with 134.1.4 without using glands (why anyone would do so I don't know, but it can be done) in which case the armour would not need earthing, also, if connected with appropriate glands and then shrouded, then you are correct, the armour would still not need earthing. That is unless you are burying your cable underground or in a wall at a depth of less than 50mm.

Some may even argue that because a steel wired armour cable contains within its armour conductors that are housed in basic insulation which are in turn then sheathed that the inner part of the cable meets the requirements for both basic and fault protection therefore meaning that the armour cannot be by definition an exposed conductive part.

I am by no means advocating not terminating and glanding SWA in accordance with the standard of widely known best practice, I am merely stating that the armour is arguably neither an exposed or extraneous conductive part meaning that unless specifically required, does not need earthing or bonding.

 

[44ALLAN]

"I am by no means advocating not terminating and glanding SWA in accordance with the standard of widely known best practice, I am merely stating that the armour is arguably neither an exposed or extraneous conductive part meaning that unless specifically required, does not need earthing or bonding".

I now your not mate but there would be no need to use Swa if you weren't going to gland it surely?
What would be the point...........mechanical protection !!
The cable then gets damaged and you have a phase ( or line lol ) fault to the armour but it isn't earthed?

IMO the armour is an exposed conductive part as its part of the system and always will be and therefore needs to be earthed.
That's the way I do it anyway lol.
How can it 'not' be an exposed conductive part?
If someone puts there spade or digger through it you would want it earthed surely?

 

[D Skelton]

I now your not mate but there would be no need to use Swa if you weren't going to gland it surely?
What would be the point...........mechanical protection !!

I totally agree!

IMO the armour is an exposed conductive part as its part of the system.

Being part of a wiring system doesn't neccessarily make it an exposed conductive part. Look up the definition in Part 2.

If someone puts there spade or digger through it you would want it earthed surely?

That's exactly why 522.6.100 calls for it to be earthed if buried. That still doesn't make it an exposed conductive part though.

 

[44ALLAN]

I'm getting old mate lol.

Exposed conductive part............can be touched/can become live under fault.

The shroud can be removed leaving the gland accessible or the sheathing could be damaged......that makes it 'exposed' in my book
An internal or an external fault could make the armour live.

I would always earth the armour in case of these events.........not after they happened

All down to interpretation though isn't it mate I suppose.
Good discussion tho

 

[D Skelton]

Exposed conductive part............can be touched/can become live under fault.

And fault protective provisions provide protection under single fault conditions.

An internal fault could make the armour live.

Only if both the insulation and sheathing was ruptured, making it a double fault. As above, we are only required to protect against a single fault.

An external fault could make the armour live.

An external fault could also make your car live, or your window frame, or your bed frame, or your cutlery, or even the frame of your glasses live.

I would always earth the armour in case of these events

As would I!

Good discussion tho

I do love a good old debate me

 

[Jay Sparks]

I was always taught to earth the armour at the supply end, no matter how it was installed. Obviousley, if the armour is being used as a cpc, then both ends. So, although it may not need to be earthed, I always do and I thought that was the norm??

 

[Jay Sparks]

An external fault could also make your car live, or your window frame, or your bed frame, or your cutlery, or even the frame of your glasses live.

Are you Mr Cokburn in diguise??? lol Only kidding!!

 

[44ALLAN]

Originally Posted by 44ALLAN
Exposed conductive part............can be touched/can become live under fault.
And fault protective provisions provide protection under single fault conditions.

An internal fault could make the armour live.

Only if both the insulation and sheathing was ruptured, making it a double fault. As above, we are only required to protect against a single fault.

So in effect your saying the armour of cable is 'not' an exposed conductive part?.
Well I neva lol

Originally Posted by 44ALLAN
An external fault could make the armour live.

An external fault could also make your car live, or your window frame, or your bed frame, or your cutlery, or even the frame of your glasses live.

I meant an external fault on the cable...... as in a spade going through it lol.

Totally agree about debating that's why I asked in the first place..........live and learn as they say.

 

[MDJ]

If I'm running two core 25mm SWA as the submain with a 16mm (non-armoured) earth seperately then will the earth require its own mechanical protection?

Also as regards earthing the armour wire - will 6mm (from the tag to the earth block) be sufficient as it now counts as extraneous metalwork?

Nothing wrong with it, but I use 10mm2 ---16mm2 TBH for the banjo link.

 

[D Skelton]

I was always taught to earth the armour at the supply end, no matter how it was installed. Obviousley, if the armour is being used as a cpc, then both ends. So, although it may not need to be earthed, I always do and I thought that was the norm??

It is the norm lol, I'm not saying it isn't, just that the norm isn't neccessarily required by regulation. All I did was explain the facts regulatory speaking, not neccessarily what we should do as professional sparks.

I would like to think that everyone here adhears to the norm, I include myself in this, but... Imagine an EICR scenario, you couldn't just immediately code an unearthed sheath as a C2 or even a C3 without a bit of thought because strictly speaking, there may be nothing wrong with it regulation wise! Maybe they just ran out of NYY and were to lazy to buy more lol.

 

[D Skelton]

So in effect your saying the armour of cable is 'not' an exposed conductive part?.
Well I neva lol

Yep lol

I meant an external fault on the cable...... as in a spade going through it lol.

Well the only risk of that is if the cable is buried, in which case as I have said three times now, there is a specific requirement to earth buried SWA!

If it aint buried, unless you are a complete moron, you're not going to be digging through your wall mounted SWA are ya haha!

 

[Outspoken]

For 25mm² cables the armouring needs to have a csa of 70.09mm² to be compliant.

So use the adiabatic equation, as already mentioned above but others, to calculate the minimum csa of your cpc and see where that leaves you..

The big question of course is the disconnection times...depending on the length of the sub-main will you achieve the required disconnection times for the circuit in the event of a fault.

I appreciate that in 98% of cases the armouring will meat all your needs, but if it is a long run it may be worth doing the calcs to confirm..

 

[44ALLAN]

If it aint buried, unless you are a complete moron, you're not going to be digging through your wall mounted SWA are ya haha!

I once called my mates sister a right slapper ......not realising she was standing behind me !
Does that count in the moron stakes? :sad3: