TT System testing and results

[AdamDee]

Hi Guys,

I have been testing for about a year and have come across my first tt system yesterday.


I disconnected the earth and tested for Ze and got 8.67 ohms which I believe to be a great reading as osg allows up to 200 ohms. I couldn't do a Ra reading as the rod is under the house and impossible to get to.

But when I'm doing all the earth loop tests on all the circuits I'm getting similar readings between 7ohms to 9ohms. As I havent tested this before and not really sure on it I dont know what im doing wrong, what the problem is and how to fix it? So any help would be great if possible.

Many thanks.

 

[monkeyelectric]

Whats wrong with that? If your Ze is 8.67 then your Zs readings will all be around that figure too

 

[bigbaddave]

Probs getting better connection with parralel paths from water and gas assuming main bonding is present. That's if readings are lower. As monkey said there usually very close anyhow. What were you expecting?

 

[bigbaddave]

There's nothing to fix tho. You have confirmed your reading complies and there is external earth. Note figures on cert and move on. Simples.

 

[AdamDee]

Whats wrong with that? If your Ze is 8.67 then your Zs readings will all be around that figure too

So thats fine? Osg says 1.16 for type b 32a mcb. So how can 7ohms be acceptable?

 

[Richard Burns]

All circuits on a TT must be protected by an RCD so that earth faults will cause disconnection, a L-N fault will disconnect the MCB but a L-E fault will only disconnect the RCD. The RCD only needs 30mA and you would have about 29A with that Zs.

 

[Octopus]

Hi Guys,

I have been testing for about a year and have come across my first tt system yesterday.


I disconnected the earth and tested for Ze and got 8.67 ohms which I believe to be a great reading as osg allows up to 200 ohms. I couldn't do a Ra reading as the rod is under the house and impossible to get to.

But when I'm doing all the earth loop tests on all the circuits I'm getting similar readings between 7ohms to 9ohms. As I havent tested this before and not really sure on it I dont know what im doing wrong, what the problem is and how to fix it? So any help would be great if possible.

Many thanks.

That's an impressive Ze on TT - did you disconnect the water and gas bonding?

 

[telectrix]

So thats fine? Osg says 1.16 for type b 32a mcb. So how can 7ohms be acceptable?

it's acceptable because , with a TT system and 30mA RCD the max. Zs for a circuit is 1667Ω.
.

 

[AdamDee]

it's acceptable because , with a TT system and 30mA RCD the max. Zs for a circuit is 1667Ω.
.

Ok great. Thanks for the help.

 

[Des 56]

I mean no disrespect to Adamdee because you only experience whats in front of you,this is a general forum moan

The amount of threads that contain very confused folk in this subject is very surprising.
It would seem to be essential to obtain this understanding
,I am sorry to say a TT system is well documented type,its in all the books and should be understood even if it has not been experienced

 

[Octopus]

I mean no disrespect to Adamdee because you only experience whats in front of you,this is a general forum moan

The amount of threads that contain very confused folk in this subject is very surprising.
It would seem to be essential to obtain this understanding
,I am sorry to say a TT system is well documented type,its in all the books and should be understood even if it has not been experienced

But rarely taught

 

[monkeyelectric]

So thats fine? Osg says 1.16 for type b 32a mcb. So how can 7ohms be acceptable?

Is it protected by a 30 mA rcd?