Pfc on a tt

[flukey]

hi all,
tested a board on a house today, TT system and got a PFC reading of 50 amps
does this sound right
ZE is just over 7 ohms

 

[Guest123]

Higher the impedance lower the fault current matey.

By calculation I get about 33A so your about right.


Good Ra of 7 ohms mind.

 

[flukey]

cheers lenny, been a long day mate

 

[pevvers]

Did you check the line to neutral fault current as well? As that will also play a part as the PSCC, as the highest of the PEFC and PSCC is the one that goes in the PFC box...

 

[glasgowspark]

assuming single phase all is well in your calculation.

Bear in mind in 3 phase calculation you will need to double the final answer.

 

[opm electrical]

does anyone else seem to get higher pssc on a tt. i got pssc of 11 ka on on the last couple i tested

 

[trebor]

The system in pscc measurement is not relevant as you are measuring between line and neutral, it is only pefc which is relevant to sytem earthing as it taken between line and cpc

also with pefc unlike Ze it is taken with the earthing conductor connected to include any parallel earth paths that may be present, hence in an industrial unit with a lot of structural steelwork to ground the pefc may well be higher than pscc and then is recorded as pfc on the cert