Because I have a high ELI reading with my TT earthing - around 620 ohms
- I want to drive in some new copper rods to see if I can improve it. My question is about the size of the cable from the rods back to the CU. I know that 10mm would be ideal, but because I have a 50 metre reel of
6mm, and I would have to buy in some 10mm, I would prefer to use that. The run back to the MET would be about 6 to 7 metres, so would the 6mm be acceptable?
Yes.
2.5mm is acceptable if it is not buried, and protected from corrosion and mechanical damage. So 6mm is fine if not buried, and protected from corrosion.I'd always go for the 10mm, as, well, it just looks 'safer' as it is a fatter cable! Also, I dont keep 6mm cable. The differences in impedance in that short run is very small, so a fault will take maybe a millisecond more to trip the RCD. In real life, there will be no measureable difference.
Any reason not to run two bits of 6mm side by side?
Cheers
Dave R
Many thanks for that.
Interesting idea, I'll certainly consider that. Many thanks.
6mm is overkill, and fine
NT
I was a bit concerned by the electrician that came to do the wiring of my PV panels who expressed concern at my earth having 98 ohm resistance - "Yes, it's TT; and thanks for confirming that it is as low as that!".. Puzzled look, followed by "Is that the size of your earth wire - it should be 10mm" -- "and what would the point of that be when it's feeding into 98 ohms?". Went away grumbling.
Rob
The various combinations of requirements are summarised here:
The most common situation is that insulated single wire (6491X) will be used as the earthing conductor, and will be buried for some of its length. The PVC insulation gives corrosion protection, but not mechanical protection. Therefore the correct size to use for most TT installations is 16 mm^2.
Note there is a broken external link to an IEE Wiring Matters article in that.
The article in question is contained in this:
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