Sub Main and seperate earth

[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: