Main Protective Bonding Conductors

[OnOff]

I've been on site this week and had the opportunity to watch some subbed in sparks running cabling for a 3-phase changeover switch. The cables in question are each 1x300mm sq single core armoured routed on a tray each with a current carrying capacity of over 600A. They have run 4 cables i.e. 3P+N. I happened to overhear a conversation, something on the lines of "They haven't sent any earths!", and half jokingly asked if they were going to use the armoured. The guy responded on the lines of "What you mean use the banjos?".

Anyway today I see they have NOT run a separate CPC and one of them confirmed they would be using the armoured.

It got me thinking as to whether this is correct and I dug my regs out later. Looking at TABLE 54.8 it suggests a minimum COPPER equivalent CSA for the main protective bonding conductor of 50mm sq where the supply neutral is over 150mm sq (as I said its 300mm sq).

Is it the case then that that the combined CSA of the armoured on all 4 cables that have been run would exceed 50mm sq? I'm guessing it would. Even then, it's not copper I'm thinking.

Good practice, pulling the wool, me missing something etc?

All comments appreciated.

 

[ElectekAir]

Even though what they have done will satisfy the regs I would not want to rely on the SWA for the earth because it is made up of 8 connections, would be better to run a separate CPC

 

[kerching]

If it is single cored armoured then I would have thought the armouring would be Aluminium [A.W.A.], so that has a few issues of its own If I recall correctly............. :coat

 

[OnOff]

If it is single cored armoured then I would have thought the armouring would be Aluminium [A.W.A.], so that has a few issues of its own If I recall correctly............. :coat

Didn't get a chance to look at the construction...........will try next week. Cleveland Cables from memory on the label.

---------- Post Auto-Merged at 17:11 ---------- Previous post was made at 17:03 ----------

Even though what they have done will satisfy the regs I would not want to rely on the SWA for the earth because it is made up of 8 connections, would be better to run a separate CPC

It just seemed a bit cheapskate possibly sly to me. But then I got to thinking I bet the cost of a roll of CPC split between the bloke who ordered the works and the bloke fitting it would see them get a few quid each............or as a lad said to me in the tea room later "There's the real world and what's in 'your' regs.......if you did it properly nothing would ever get done!".

 

[kerching]

Didn't get a chance to look at the construction...........will try next week. Cleveland Cables from memory on the label.---------- Post Auto-Merged at 17:11 ---------- Previous post was made at 17:03 ----------

.

I will wager a slap up meal at Mrs Miggins Pie Shoppe that it is AWA. Otherwise Eddy and his little currents will visit, I think that it may even need special glands.......... :coat It just seemed a bit cheapskate possibly sly to me. But then I got to thinking I bet the cost of a roll of CPC split between the bloke who ordered the works and the bloke fitting it would see them get a few quid each............or as a lad said to me in the tea room later "There's the real world and what's in 'your' regs.......if you did it properly nothing would ever get done!"

 

[M107]

Mrs Miggins Pie Shoppe.................. ah captain slack bladder.

 

[kerching]

Mrs Miggins Pie Shoppe.................. ah captain slack bladder.

Indeed, a man after my own heart.................... :Y .................. :coat

 

[OnOff]

If it is single cored armoured then I would have thought the armouring would be Aluminium [A.W.A.], so that has a few issues of its own If I recall correctly............. :coat

Just managed to take a look and it IS AWA (so my magnet says anyway).........so I assume the combined csa of the 4 aluminium armoureds satisfies the earthing requirements? Cheers.