G
Gardner
What is the max resistance at the time of installation permitted on customer earth rods in a TT supply?
Discuss TT earth electrode in the UK Electrical Forum area at ElectriciansForums.net
What is the max resistance at the time of installation permitted on customer earth rods in a TT supply?
200 Ohms is what is considered to be stable, ideally you should be aiming for a reading considerably lower than that, i small nest of rods i recently fitted, I achieved 2.5 Ohms.
I guess I should drive them deep even if I get a low ohm reading with a 6 foot rod in the event the top layer of earth dries up.
I guess I should drive them deep even if I get a low ohm reading with a 6 foot rod in the event the top layer of earth dries up.
obviously you're not in the UK. it's almost permanent monsoon here. nothing can dry up. :devilish:
I thought you were NICEIC? Their version of that utter nonsense is 100ohm not 200.
Why exactly is 200 ohms max idiotic Dave ? With a decent quality 30 ma RCD you'll get perfectly reliable and acceptable [fast] disconnection times under fault conditions at much higher Ze than that. Here in Cornwall the ground is often very hard and rocky and you could easily spend a whole day trying to get multiple rods in and that would be with some luck, just not competitive I'm afraid.
I thought you were NICEIC? Their version of that utter nonsense is 100ohm not 200.
Very true, personally being one with little experience of TT systems I aimed on that last one to get a good reading and didn't want to settle for any less.
what I would say is that I measured the rods as I drove them in and it's very true that the deeper you go the better the result so I can only recommend going as deep as you can.
i think 3 rids deep it's quite s good depth and not too difficult to get to with a lump hammer if you don't have a better method of driving them in.
i think there's a limit to how far you go with a nest as you might keep banging rods in nice and deep and joining them together and it not making much difference so to you accept defeat at say 80 ohms or do you keep trying?
the only reason I kept going was because it seemed easy Ish to put them in and each stack gave good results.
The regulations require that a stable and reliable value of Ra be achieved.
What is stable will depend entirely on ground conditions and soil resistivity.
Deep rods in multiple locations are the key to achieving stability.
No doubt someone will come on here to quote the idiotic 200ohm nonsense which has been misconstrued from a note in the regulations. The NICEIC have their own version of this which is 100ohm.
The problem it seems is that there are a lot of people who can't cope with the idea that a good and stable value will be very different in different parts of the country.
A value of 300ohms achieved with 4x 8' rods will be much more stable and therefore better than 50 ohms achieved with a single 4' rod
Ah I mistakenly thought that you meant 200 ohms was too HIGH Dave, but seems we're on the same wavelength.
Reply to TT earth electrode in the UK Electrical Forum area at ElectriciansForums.net
We get it, advertisements are annoying!
Sure, ad-blocking software does a great job at blocking ads, but it also blocks useful features of our website. For the best site experience please disable your AdBlocker.