S
sbelec
Hi,
Can someone explain the science behind the need for 10mm earth cables to gas, water etc? Or is this simply a justifiable rip off for big companies as the size required has gone up slowly over years - the main reason so many DIYers have a go!
A 100a fuse feeds a consumer unit through 25mm cable, normally a couple of meters at most. The house is then fed through a whole series of smaller cables with the absolute maximum being 16mm if you have a 12kW shower and even then the CPC is only 6mm. So if 6mm is sufficient for a disconnection time of 5 seconds why do we use 10mm on water and gas?
The reason this has really come home is I am running a 4mm SWA to an outhouse (2m from main house) where there is a water supply that needs bonding back to the main earth terminal. The supply is via a 32amp mcb, yet I have got to have a 10mm earth cable - whats the point! My original plan was 3core, 1 core for my CPC and the armour would be sufficient for 9.5mm equivalent copper. Technical viewpoint is it MUST be 10mm and this is no good.
Then of course we add the fact that the water supply is plastic in many house to the tap, one house I went to with a plumber recently had a plastic in to the tap and then 150mm of copper and a plastic tee split to 2 plastic pipes with an earth clamp.
Of course the owner is questioning this as to why with RCD protection I am pushing for everywhere and he can understand does he need to take out perfectly good 6mm which to be blunt other than the BGB I actually agree with him. Lets face it 1440 ohms is sufficient to trip an RCD.
Sorry rant over, but is there a scientific proven reason for the size? Other than protection against damage. This is definately an area IET must address BEFORE they rip us off with another book and using the real world, sorry but do they employ electricians or electrical engineers.
steve
Can someone explain the science behind the need for 10mm earth cables to gas, water etc? Or is this simply a justifiable rip off for big companies as the size required has gone up slowly over years - the main reason so many DIYers have a go!
A 100a fuse feeds a consumer unit through 25mm cable, normally a couple of meters at most. The house is then fed through a whole series of smaller cables with the absolute maximum being 16mm if you have a 12kW shower and even then the CPC is only 6mm. So if 6mm is sufficient for a disconnection time of 5 seconds why do we use 10mm on water and gas?
The reason this has really come home is I am running a 4mm SWA to an outhouse (2m from main house) where there is a water supply that needs bonding back to the main earth terminal. The supply is via a 32amp mcb, yet I have got to have a 10mm earth cable - whats the point! My original plan was 3core, 1 core for my CPC and the armour would be sufficient for 9.5mm equivalent copper. Technical viewpoint is it MUST be 10mm and this is no good.
Then of course we add the fact that the water supply is plastic in many house to the tap, one house I went to with a plumber recently had a plastic in to the tap and then 150mm of copper and a plastic tee split to 2 plastic pipes with an earth clamp.
Of course the owner is questioning this as to why with RCD protection I am pushing for everywhere and he can understand does he need to take out perfectly good 6mm which to be blunt other than the BGB I actually agree with him. Lets face it 1440 ohms is sufficient to trip an RCD.
Sorry rant over, but is there a scientific proven reason for the size? Other than protection against damage. This is definately an area IET must address BEFORE they rip us off with another book and using the real world, sorry but do they employ electricians or electrical engineers.
steve
