Maximum Ze Values

[ch1cki]

Ze values on;

TNCS
TT
TNS

 

[DurhamSparky]

TNCS 0.35
TNS 0.8
TT = RA of 200 ohms!

 

[james king]

as he says

 

[sparkiegaz]

mmmm on site guide get one bloody handy

 

[IQ Electrical]

If this is an exam question then the usual supplier values quoted are:

TN-S 0.8 Ohms

TN-C-S 0.35 Ohms

TT 21 Ohms

The TT value is the sum of the resistances of the suppliers transformer winding, suppliers electrode (Rb) and the line conductor from the transformer to the consumers installation.

The recommended Ra figure varies from 100-400 Ohms depending on what publication you put your faith in!

 

[DurhamSparky]

The recommended Ra figure varies from 100-400 Ohms depending on what publication you put your faith in!

i prefere to follow the BRB and disregard all other nonsense!! especially if it has a NIC Logo attached to it!

 

[sinaloan]

what page of the onsite guide is this on?

 

[Sparky Ninja]

what page of the onsite guide is this on?

Page 11

 

[sinaloan]

cheers widdler

 

[learnedfriend]

And if I have a reading of 1.09 ohms on a TN-C-S system? With a fault current of 224? I'm guessing its time to tall in Western Power to get the Loop Impedance reduced?

 

[pmanku]

If your reading is for Ze at the supply origin then yes this is high for a TN-C-S supply and this indicates a problem with either the test procedure or the supply wiring. Confirm again the result ....before calling DNO...avoids red face

 

[Guitarist]

And if I have a reading of 1.09 ohms on a TN-C-S system? With a fault current of 224? I'm guessing its time to tall in Western Power to get the Loop Impedance reduced?

Make sure you are taking the Ze reading with a high current, not a no-trip 2-wire test. Tested a TNC-S system today with my Megger 1730...Always do high current but thought I'd see what the no-trip gave me.. Ze=0.19 ohms 2-wire high current/1.06 ohms 2-wire no-trip.

 

[GLENNSPARK]

TNCS 0.35
TNS 0.8
TT = RA of 200 ohms!

no...max Ra is 100 ohms....Tony Cable and the NIC say so.....so its got to be true...

 

[richy3333]

Make sure you are taking the Ze reading with a high current, not a no-trip 2-wire test. Tested a TNC-S system today with my Megger 1730...Always do high current but thought I'd see what the no-trip gave me.. Ze=0.19 ohms 2-wire high current/1.06 ohms 2-wire no-trip.

Lol I did that too. DNO emergancy service operative had a 3 hour round trip and I had to call him and apologise but point out his overtime!

 

[GLENNSPARK]

but not to worry....once you get to within 200 ohms (or 100 ohms if NIC)...then pack your tools...jobs a good un.....