High Ze on a TNCS system

[Guest123]

Hi James.

Sounds like you will need an Electrical Installation Certificate for each one of those jobs.

You can download certificates from the IET website or you should be able to buy them in the wholsalers i.e Robin own brand or Kewtech etc etc.

NIC will also sell you the green certificates I think you mean.


With regard to your PFC, this is in relation to your Ze as the impedance of the earth fault path will restrict the amount of fault current that will flow.

So with the Voltage of 230V and Ze of 2100 - 230/2100 = 0.11A, which isn't enough to cause your MCB/fuses to operate in the required time before the safe touch voltage of 50V is exceeded!!!! so that's why RCD protection is needed on TT system...I hope you have RCD there as you are in quite a bit of danger if not.

You really need to get the Ze (Ra) down to below 200ohms ASAP and RCD if not already present.


HTH

 

[james king]

yes at the mo my metre reads <1A all circuits r rcd protected what is maz pfc reading on tt tns tncs?

 

[Guest123]

The max fault current is limited by the KA rating of your protective devices i.e, a Type B BS 60898 MCB is rated to a max of 6KA, BS 1361 Type 2 (suppliers fuses) are rated to a max of 33KA.

 

[james king]

thanks lenny ur a great help!1 other thing i have for got the R2 test for lighting and ridal sockets all that is is conect live and cpc at the CU and test from socket or lighting point eg only fil in r2 test slot leave r1 and r2 blank????

Ze test is from incoming live incoming nut but with a dissconneted earth and test between live and nutral and earth bar? i done it to day got a reading of 0.18ohms and a Zs of 0.08 i think off top of my head il have a lok at test sheet?

 

[Guest123]

thanks lenny ur a great help!1 other thing i have for got the R2 test for lighting and ridal sockets all that is is conect live and cpc at the CU and test from socket or lighting point eg only fil in r2 test slot leave r1 and r2 blank????

Right, the test you have described there IS the R1+R2 test i.e linking line and CPC at CU and testing at extremity of the circuit.

The R2 test is the "long lead" test whereby you connect one end of the lead to the CPC at the CU and test betwen the other end of the lead and CPC at the extremity of the circuit.


Ze is measured by turniing off all breakers RCD's and main switches, disconnecting the main earthing conductor from the earthing terminal/bar and testing between this disconnected conductor and L+N at the feed side of your main switch.


Zs is measured with all conductors re-connected, all breakers, RCD's and main switches re energised and taking a reading at the extremity of each individual circuit.


HTH.

Ps, make sure you get that copy of GN3.

 

[james king]

yes i will b going denmas mon morn to get one its all cuming bk to me now

r1 and r2 for final ring is crossing over cpc and live from oppisite cables.

got a diagram for u to c il put it on nw on ze

how do u do it lol

 

[Guest123]

Dont be confused by r1, r2, and R1+R2.

They are different tests altogether.

 

[james king]

sorry can u explain?

r1=
r2=
r1+r2=

would rele help!!

 

[Guest123]

sorry can u explain?

r1=
r2=
r1+r2=

would rele help!!

r1 = end to end test of LINE conductor of a ring circuit at the CU
rn = end to end test of NEUTRAL conductor of ring circuit at the CU
r2 = end to end test of CPC of ring circuit at CU

R2 is the long lead test I mentioned earlier

R1+R2 is the linking out of LINE and CPC of a RADIAL circuit at the CU and measuring at the extremity of that radial circuit

OR

Cross connecting L1 + CPC2, and, L2 + CPC1 conductors of a RING CIRCUIT at the CU and measuring at each socket outlet on that ring circuit.

 

[james king]

yes got it now thank u!! funny how if u dont test for a long time u forget every thing isit it even tho i got 17th 2391 and 2330 L2 L3 LOL

ONE MORE TEST I WANT TO KNOW AND IF U COULD HELP IS SHORT CIRCIT TEST? I KNOW U HAVE TO TAKE THE HIGHEST READING EITHER FROM PFC OR SHORT CUIRCIT??

 

[Guest123]

PFC is the higher of the two readings of PEFC and PSCC.

PEFC is measured L-E, PSCC is measured L-N.

On a 3 phase system as a rule of thumb, the PFC is doubled as the highest fault current would be between phases.

 

[james king]

Ok thanks lenny very helpfull o ye if any one can help with what question the assessor will ask with the answers u would give with b good

need all info i can collect

cheers every 1

 

[VOLTMAN]

try amazon for gn3 its all in there good luck

 

[james king]

Ok kl thanks voltman can u give sum advice on the assessment

i neeeeeeeeeed to pass no matter what will loose lots of cash if i dont

 

[VOLTMAN]

the thing is not to panic my assessor was great hes there not to pick holes but to help . he asked me questions on earthing and did tests on r1 r2 on a lighting circuit and some rcd tests make sure you got all paper work ready for him good and plenty of tea good luck