quick bonding question

[chopper]

went to a job today we were ony swapping a light fitting but noticed the main bonding was ony in 6mm tri rated cable to the gas, the building was a old pub what is going to be used as a train station, quite a big building thought it would need 16mm earth , but lad i was with said cos it was tri rated cable 6mm would probly be fine, we had a look in regs but couldnt find owt, anyone any idea and where can i find it in rergs

 

[i=p/u]

what earthing system???

 

[chopper]

tnc -s, 25mm 3 phase 35mm n

 

[needasparks]

Not uncomon to find undersized earthing, worth mentioning to the client about it and indicate an inspection is due.
From what you say the pub is closing i guess they won't bother having it done and when its a train station its under different regs to ours so not an issue as was in place for the work you did although possibly undersized but you would not know that unless it was tested first.

 

[chopper]

had a look in regs, it just says 35mm to 50mm neutral requires 10mm cross sectional are, but is normal stranded 10mm cable diffrernt to 10mm tri rated cable, what the lad was saYING is cos its try rated its equalivelent to 18mm cable, never come acroos this and cant find anything in regs,
also what regs does it come under cos they on about making it a train station with offices

 

[needasparks]

Railways, Mines, offshore etc are under their own regs and excluded from BS7671. I used to work on the railways, it was a nightmare.

 

[chopper]

ok yeah i understand that but still cant find anything about this bonding im interested lol

 

[Richard Burns]

tnc -s, 25mm 3 phase 35mm n

Minimum size for bonding with PME is 10mm2 copper for current regs (544.1.1). The current carrying capacity of the cable is not considered and so even though you have an additional 6 amps CCC with tri rated cable (which is still less than 10mm2) this will make no difference to the size of bonding required.
As needasparks says let them know but it probably complied when it was built.

 

[chopper]

been told by the audiabatic equation that it complies

 

[chopper]

guess its just the normal on site rule of thumb that throws us

 

[i=p/u]

so what was you (I) in you calculation or what size of fuse =chopper;409781]been told by the audiabatic equation that it complies[/QUOTE]

 

[Richard Burns]

Since the adiabatic equation does not apply to bonding conductors it is difficult to see how it can comply with the adiabatic equation. the main bonding conductors are selected according to the size of the neutral supply.

I would agree that the bonding conductor is probably suitable, but it does not comply with current regulations.