Highest ze on a tt

[monkeyelectric]

We've had a lowest thread how about the highest? obviously scuppered a bit by how high the tester goes but i've had 1147ohms once, terrible ground

 

[Spudnik]

450 ish here.

Couldnt find the rod so banged in new.

 

[Bobby B]

700, took 3 more rods to bring it down to 160

 

[monkeyelectric]

Same with that one of mine and i had to kango them in, nearly gave up to be honest got it to 180 ish, good enough for me

 

[scotsparky]

there is a a product (cant remember the name) its basically crushed volcanic ash which can be used at earth rods to help lower reading. it sucks up all moisture and holds it and so reducing resistance. will did out the name soon.

a) a clay based material formed by the​

decomposition of volcanic ash, such as bentonite

 

[zone77]

i just pee on em

 

[Jason Smith]

Just read on the voltimum site that up to 1660 ohms is acceptable for a TT reading, and it is accepted that over 200 tripping times become unreliable. Will go back to it in a minute but can we discuss this aspect. every one seems to think under 200 is the maximum standard, and me too, have always managed to acheive it so far, thanks to the tips on here.

 

[monkeyelectric]

Just read on the voltimum site that up to 1660 ohms is acceptable for a TT reading, and it is accepted that over 200 tripping times become unreliable. Will go back to it in a minute but can we discuss this aspect. every one seems to think under 200 is the maximum standard, and me too, have always managed to acheive it so far, thanks to the tips on here.

On a 30mA rcd its 1667ohms, 200 is the standard as anything above that is classed as unstable niceic like to see less than 100 though

 

[Guest123]

Hi

Dont be confused by max Ra (rod resistance), 200ohms as suggested in BS 7671 and, max permitted Zs when a circuit is protected by a 30mA RCD = 1667ohms.

 

[gnselectricals]

doin a periodic today on a caravan site in swansea had 498 ohms, my highest so far

 

[Guest123]

Just had mine on a PIR yesterday........1072ohms!!!!

 

[Marx]

Just had mine too, on a C/U change, over 1000ohms. Banged three more rods in and got it down to 800. Back next week armed with 10 more rods, bag of Pompeii's finest and three flasks of coffee!

 

[GaryM]

Hi

Dont​

be confused by max Ra (rod resistance), 200ohms as suggested in BS 7671 and, max permitted Zs when a circuit is protected by a 30

mA​

RCD = 1667ohms.

And 542.2.2 to go with it - "The type and embedded depth of an earth electrode shall be such that soil drying and freezing will not increase its resistance above the required value."

 

[Scott F]

Hi

Dont be confused by max Ra (rod resistance), 200ohms as suggested in BS 7671 and, max permitted Zs when a circuit is protected by a 30mA RCD = 1667ohms.

Lenny I do not have that much experience with TT so forgive me, But I know we need a low Ze But isn't it the

Zs that really counts ?

An excerpt from snags and solutions earthing and bonding that I happened to be reading today in the Van.

Talking about an upfront time delayed 100ma rcd (Snag 10) where RA needs to be below 500 ohms

"These values are normally easily obtainable but, unless there are good reasons to expect such high values

such as hard /rocky ground" ---I have to go back to a property next week that has about 565 ohms .

However its concrete on top of slate and slate bedrock Every thing on 30ma Rcds . what would you do in

that situation keep on banging rods till it gets lower and if so how many would you bang in ?

 

[Guest123]

Well mate you do need to get it to below 200ohms really.....NIC ask for less than 100 but lets not worry about them for now.

You could try adding more rods, at least the length of the rods apart. Bentonite is cracking stuff, need to make bigger holes in the ground though for it to be of any use.