PME head , builder forgot earth cable , 100amp 3phase supply , 10 bedroom house , 10 bedroom house

[westward10]

Must admit I find this worrying unless they are misinterpreting the query.

 

[Pete999]

You have to remember that some of the chaps on the helpdesk are not sparks

Perhaps that's why they are called scams, you would have thought the guys at the sharp end (the help desk) would be suitably clued up, qualified Electrical People, well you would wouldn't you?

 

[andysparkfree]

I spoke clearly and slowly

im gona go through my paper works tonight as i think i got a printout that relates to swa armouring that was provided to me by the nic a few months back (admittedly i didn't look at it )

 

[Pete999]

I spoke clearly and slowly

im gona go through my paper works tonight as i think i got a printout that relates to swa armouring that was provided to me by the nic a few months back (admittedly i didn't look at it )

Just checked my notes and found this info a 35mm2 4 core SWA has a steel csa of 78mm2 equivalent to a 25mm2 copper conductor (BS 4567 & 6724) and 84mm2 steel 32.7 copper (BS 6346)

 

[westward10]

Just checked my notes and found this info a 35mm2 4 core SWA has a steel csa of 78mm2 equivalent to a 25mm2 copper conductor (BS 4567 & 6724) and 84mm2 steel 32.7 copper (BS 6346)

You need to know the conductivity of the armour not what it's copper equivalent is and I suspect this is where it is going wrong.

 

[Pete999]

You need to know the conductivity of the armour not what it's copper equivalent is and I suspect this is where it is going wrong.

Table 5 OSG I think

 

[Pete999]

You need to know the conductivity of the armour not what it's copper equivalent is and I suspect this is where it is going wrong.

I believe the calculations that the figures I have mentioned have been calculated using the K factors.

 

[westward10]

GN8 advices on factors to be used when the material for the main protective bonding is not copper so it's conductivity can be calculated. This will apply in the OPs case as the armour is being used to support the bonding.

 

[Pete999]

GN8 advices on factors to be used when the material for the main protective bonding is not copper so it's conductivity can be calculated. This will apply in the OPs case as the armour is being used to support the bonding.

The conductivity has been factored in, I thought we were trying to ascertain if the armour was large enough to cater, for both the main earth, and the main bonding conductor. in this case it clearly is not suitable size wise, which incidentally makes a mockery of what the scam has told the OP.

 

[Leesparkykent]

The coefficient restivity of copper at 20 degree C is 0.004, the restivity of steel changes with carbon content hence the guidance in GN8. I believe GN8 gives a ratio of 1:8.5. So If 10mm copper is deemed adequate as the CSA of a bonding conductor but you want to use the Steel armour as the bonding conductor or forming part of a bonding conductor then you need to apply the ratio that's provided in GN8.

10mmx8.5=85mm

The CSA of 35mm 4core XLPE armoured cable is 78mm

78mm is smaller than the required 85mm.

As its smaller than the required CSA it's not deemed adequate to use as or form part of a bonding conductor.

 

[elsparko]

not just ram a ruddy big rod into the ground and run a 25mm CPC to it?

 

[andysparkfree]

ok so you guys have put the case forward that the Nic must have got it wrong , and to be honest after reading your facts and calculations i think you must be right !
so going to tell builder get the block paving up again /dig out the trench and we will install the earth
better to be safe than sorry!

 

[westward10]

Top man.

 

[elsparko]

ok so you guys have put the case forward that the Nic must have got it wrong , and to be honest after reading your facts and calculations i think you must be right !
so going to tell builder get the block paving up again /dig out the trench and we will install the earth
better to be safe than sorry!

dont tell the builder, just show up with a sledgie and start battering the slabs.

you could also run an overhead with a steel support cable, i imagine theres going to be an argument when you ask him to lift all the slabs.

why cant you just drive an earth spike into the ground with a decent CPC? seems easier than lifting 35metres worth of slabs and digging a trench

 

[HandySparks]

... with a decent CPC?

Don't you mean EC?

 

[westward10]

Whether he digs a new trench or employs TT, the main thing is that he is no longer relying on the armour.

 

[elsparko]

Whether he digs a new trench or employs TT, the main thing is that he is no longer relying on the armour.

may as well use it as a back up anyways since its there

 

[elsparko]

Don't you mean EC?

probably, as its really not a circuit, i really should learn to read my own posts before i hit send.