Help with tt system certification

[Simon81]

HiCan anyone help me with regards to filling in a niceic part p cert with regards to the part were it concerns tt.This is on page 2 I need help with the parts electrode resistance ra , is this the measured ze result I have taken ?And also method of measurement ? Also what is the maximum ze for a tt system , I no it's 0.35 for tncs and 0.80 for tns. Any help is appreciated Thanks

 

[Octopus]

I've got some sympathy for the OP here.

The OSG defines limitations for TNCS and TNS very well but when it comes to TT is less than clear having 200 ohms or 100 ohms for the Re/Ra doesn't help. When it comes to main bonding its the same ambiguity.

Lets hope such "details" are clearer when the next edition of the OSG comes out.

For what its worth I'm with the NICEIC to aim for sub 100 ohms, and I'd like to see main bonding brought into line with TNCS and TNS too.

Tin hat on!

 

[Des 56]

I dont think its unreasonable to expect an electrician to have an understanding of most of the requirements of a TT, even if they come upon them only occasionally

 

[Deleted member 9648]

Once again Simon I apologise for the tone of my post,although I stand by the gist of what I was trying to say.
At least you have asked for the correct information,rather than fabricating a cert in the pub which is what a lot of blokes would do if they didnt know....(and even if they do know)

 

[telectrix]

Thanks formal your replys got a ze of 4.69 just had a nightmare with it all. Also I have been told to enter 0.2 in the disconnection time and have been given the following maximum zs for the following mcb 6amp 38.3316amp 14.3820 amp 11.5032amp 7.19Does anyone no if this is right?

trhe bit in red is gibberish. ok.?

 

[IQ Electrical]

I've got some sympathy for the OP here.

The OSG defines limitations for TNCS and TNS very well but when it comes to TT is less than clear having 200 ohms or 100 ohms for the Re/Ra doesn't help. When it comes to main bonding its the same ambiguity.

Lets hope such "details" are clearer when the next edition of the OSG comes out.

For what its worth I'm with the NICEIC to aim for sub 100 ohms, and I'd like to see main bonding brought into line with TNCS and TNS too.

Tin hat on!

But look what he posted above regarding maximums for devices, that was just a lack of basic knowledge, never mind TT specifics!

I've got no sympathy whatsoever, he could be installing this at my mother's house!

How can we all bang on about competency and sliding standards then defend posts like this one?

If the post had started "I'm doing a TT system next week, I have a few questions.......

 

[bozobro0]

maximum zs values for 60898 type B mcbs, 6A=6.13
10A=3.68
16A=2.30
20A=1.84
25A=1.47
32A=1.15
40A=0.92 Ohms

 

[telectrix]

when you got the Ze of 4.69, was that with the main eaerth disconnected from the CU, to avoid parallel paths?

 

[mcs.serv]

But why didn't you read up on the requirements for TT before getting involved in someone's installation?

Or any other system for that matter!

 

[Simon81]

I am a compotent electrician I no the maximum zs for mcb 32 1.44 6 7.67 etc but I have been told by a fully approved niceic member that the values change when the system is tt so is he wrong is that what your saying

 

[Octopus]

I am a compotent electrician I no the maximum zs for mcb 32 1.44 6 7.67 etc but I have been told by a fully approved niceic member that the values change when the system is tt so is he wrong is that what your saying

Not wishing to be too critical, but your posts would benefit from some punctuation, and editing, before you hit the "post" button

 

[bozobro0]

As far as im aware the max zs of the device never changes,but with it being a TT system you are more than likely going to be over the max zs when testing.There are tables in the brb that you can look at to see if they are ok.Think its table 41.5,i may be wrong as i dont have my book handy at the moment,but someone may point you in the right direction.

 

[IQ Electrical]

But you must be competent on the system that you are installing!!

 

[Simon81]

Them values that I have been given are from nic software so who wrong?If the values don't change how can a ze of 4.69 and a r1 + r2 of 0.68 which gives a zs of 5.37 be within the maximum zs of a 32 amp mcb 1.44 ????

 

[Guest123]

I am a compotent electrician I no the maximum zs for mcb 32 1.44 6 7.67 etc but I have been told by a fully approved niceic member that the values change when the system is tt so is he wrong is that what your saying

Not wrong no but, it's the introduction of RCD's to cover earth fault protection due to the high Zs values that effect the changes in maximum permitted values i.e. 1667ohms for a 30mA RCD etc etc.

 

[Simon81]

I have been misinformed it seems that all an easy mistake I have been put in this position by the electricity board who wouldn't provide an earth to the property