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

 

[bozobro0]

Have you got a 17th edition regs book,there is a table in there which deals with this type of situation.

 

[mcs.serv]

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.

Correct. Table 41.5

I think what his mate is try to tell him is, what is written in the max Zs changes with TT

Max Zs = ohms1667

 

[Simon81]

He has got them values from nic software he does them on the computer and when it ask for kind of system and he enters tt them are the values for the mcb so maybe he needs to contact the nic regarding this

 

[Simon81]

Thanks for your reply bozobro also the zs you gave were slightly wrong them are at 80 percent if you look in bs7671 they are 32 1.4416 2.876 7.67

 

[bozobro0]

Iv used the NIC software before and it does automatically put the values for max zs of a device in the box for you,but the box for your actual reading goes in the measured zs.If i remember right,when you finaise the cert you will get a warning telling you that your values are high,ignore it and complete the cert.

 

[bozobro0]

Im going of the charts you get with nic certs mate.

 

[Simon81]

Yeah I no in the back I got pulled on it last year though

 

[Deleted member 9648]

He has got them values from nic software he does them on the computer and when it ask for kind of system and he enters tt them are the values for the mcb so maybe he needs to contact the nic regarding this

.....No,ignore the software and use the maximum value of Zs for the RCD protecting the final circuits. It is rare on a TT for the Zs to be within the limits for an overcurrent device,the RCD provides earth fault protection...see table 41.5 and regs 411.5.2....411.5.3.
I would suggest given your Ze that you have not disconnected the main earth lead prior to testing and parallel paths have lowered the reading.A single rod TT would normally have a Ze in the region of 50-150 ohms,or at least higher than you have recorded.


Edit....just a thought....have you provided RCD protection in accordance with the requirements for a TT?

 

[Simon81]

Just goes to prove not everyone no everything fully niceic approved contractor got his 2391 and he made me look like I don't no what I'm on about , I'll remind him not to come on this site

 

[bozobro0]

Nobody knows everything ,and if they think they do they are normally full of .I think everyone feels a bit daft asking questions and being unsure in case they get a trolling,but its better to ask and get it right than to not ask and get it seriously wrong.

 

[IQ Electrical]

Nobody knows everything ,and if they think they do they are normally full of .I think everyone feels a bit daft asking questions and being unsure in case they get a trolling,but its better to ask and get it right than to not ask and get it seriously wrong.

It's better still to ask before doing the install!!!!

 

[bozobro0]

I totally agree.

 

[Simon81]

The install was a rewire I have been put in this position by some one else I have come to test it and the earth was used off the old bonding pipe. I have done my best to rectify this I have rung the electricity board who would not earth the house leaving me to put an earth rod in I have gone well be on the means to get it done properly. I am not apologising for asking a question about a tt system I no electricians who no most thing about the regs and I have a good understanding , they couldn't help me and the one that has tried has given me wrong information which some people have jumped on me for.

 

[IQ Electrical]

The install was a rewire I have been put in this position by some one else I have come to test it and the earth was used off the old bonding pipe. I have done my best to rectify this I have rung the electricity board who would not earth the house leaving me to put an earth rod in I have gone well be on the means to get it done properly. I am not apologising for asking a question about a tt system I no electricians who no most thing about the regs and I have a good understanding , they couldn't help me and the one that has tried has given me wrong information which some people have jumped on me for.

A good understanding?

I'm out.

 

[IQ Electrical]

Thanks, most sensible post I've seen from you and almost literate.