PFC Calcs

[Nicktric]

Hi I am confused with my readings for Pefc as my Ze is .09 which would give me 2.55Ka but when I test PFC on my meter I get 5.62Ka? Ze, Neutral and earth leads clipped on disconnected main earth, probe Line on Supply side?

Can I check I am doing this correctly;3 lead PEFC piggy back Neutral/Earth clip on MET test on supply side of RCD. Pscc Clip on MET earth lead probe Line and probe Neutral supply side RCD?
Thanks

 

[Amp David]

What meter are you using?

 

[IQ Electrical]

The Ze should be measured with bonding disconnected, PFC with bonding connected to get a worst case scenario, this normally means that measured PFC is higher than V/Ze.

 

[Nicktric]

The Ze should be measured with bonding disconnected, PFC with bonding connected to get a worst case scenario, this normally means that measured PFC is higher than V/Ze.

Thanks I did the test as you described so that must be the correct result.

 

[Nicktric]

What meter are you using?

Hi Amp, It's a Kewtech three lead no trip loop/PFC

 

[telectrix]

as IQ's post. parallel paths will give you a higher value when measured than you would expect from the Ze reading. out of interest, you could re measure Ze with all the bonding and earthing connected, then re calculate PFC. ( not for the records, just to prove a point )

 

[Amp David]

On many a job having the main bonds connected won't definitely give parallel paths.

 

[telectrix]

true, but if his measured pfc is a lot higher than calculated, must be so.

 

[Amp David]

Until he tries with it with and without main bonds connected he won't now for certain if its a faulty reading that's all I mean.

 

[soar]

HI, CAN SOMEONE HELP ME ON THE PROCESS FOR TESTING Ze,
Q: isolate the supply,disconnect the main earthing conducter (MET),put the earth lead on the disconnected earth and the neutral on the supply side,and the live and the supply side,then test, and record the value? (am using a fluke 1653b)

 

[IQ Electrical]

HI, CAN SOMEONE HELP ME ON TESTING FOR Ze

I can hold the meter?

1 Isolate the installation

2 Remove the earthing conductor from the main earth terminal to eliminate any parallel paths

3 Test between line and earthing conductor at the live side of the main switch.

4 Record the result and reconnect the earthing conductor before energising the installation.

There are other text book answers regarding GS38 and other safety issues but the basic test is as above.

 

[dim_bulb]

I can hold the meter.

well what should i do then..anyone what a cup of tea?

 

[soar]

Have done the Ze,using fluke 1653B got two reading one for the PSC L-N 0.27ohm,901amps and PEFC L-E 0.36ohm,676amps, which of the highter value should i take,is it the ohm or the amps value.the R1+R2 reading for the light circuit is 2.35ohm,i should then add it to the highter value of PSC,PEFC and record it on the schedule of test results in column *12 (EFL Zs)

just trying to get on top of this,taking my 2391-10, on the 9-06-2011,so i need all the help i can get, thanks in advance

 

[malcolmsanford]

Your Ze is the test done with your main earthing conductor removed and as IQ note above you clip the disconnected earth and the LINE conductor on the supply side of your isolated switch and take the ohm reading

Your prospective earth fault current (PEFC) and your Prospective short circuit current (PSCC) is tested with the earth conductor re-connected to the MET. PEFC is done with clip to MET then to LINE and the Ka rating is taken. The PSCC test is between LINE/NEUTRAL and the Ka is taken, which ever is the highest is the value you take. Note on a TNC-S the chances are thje values will be near enough the same.

The Zs value for you lighting circuit is Zs = Ze + ( R1 + R2) so the PEFC and the PSCC should not come into the equation.

 

[soar]

well what should i do then..anyone what a cup of tea?

you can explain then to me the reading that i got from doing IR,i have loads plug in that i cant plugs, so i then, from the CCU, yes isolate the supply connect the L-N togehter and test to E and i got a reading of about 22.8 m ohm, and the fluke 1653B set on the IR 250v,that was downstair,but when i do the same test upstair with eveything unplug the reading was >200.00,which is fine i think?

 

[telectrix]

readings are fine. the 22.8Mohm is probably due to appliances still being plugged in.

 

[IQ Electrical]

If you're measuring PFC then forget Ohms, it won't be a true Ze value as bonding should still be connected.

Record the highest value as PFC.

On Ze you have to have parallel paths removed and you are measuring between line (s) and earthing conductor, highest value recorded.

Zs=Ze+(R1+R2)

 

[soar]

Your Ze is the test done with your main earthing conductor removed and as IQ note above you clip the disconnected earth and the LINE conductor on the supply side of your isolated switch and take the ohm reading

Your prospective earth fault current (PEFC) and your Prospective short circuit current (PSCC) is tested with the earth conductor re-connected to the MET. PEFC is done with clip to MET then to LINE and the Ka rating is taken. The PSCC test is between LINE/NEUTRAL and the Ka is taken, which ever is the highest is the value you take. Note on a TNC-S the chances are thje values will be near enough the same.

The Zs value for you lighting circuit is Zs = Ze + ( R1 + R2) so the PEFC and the PSCC should not come into the equation.

Sorry am getting myself mixup, i did disconnect the earth, so the value i got is 0.36ohm, 676amps, so this should record in form4 *2 and *3

 

[soar]

readings are fine. the 22.8Mohm is probably due to appliances still being plugged in.

So i should record this 22.8 M ohm in IR,L/E column *10, in sted of >200

 

[malcolmsanford]

If the 0.36 ohms is the ohmeric Ze value with the earth conductor REMOVED then yes that is the value you put on the form.

If 0.676Ka is the highest PFC value after you have RECONNECTED your earth and tested both PEFC and PSCC current then yes that is the one you put on the form.

 

[mart8235]

So i should record this 22.8 M ohm in IR,L/E column *10, in sted of >200

are you testing 2 separate circuits? upstairs and downstairs on separate circuits? if so then record 22.8Meg on downstairs and >200Meg on upstairs in relevant boxes.

 

[Nicktric]

PEFC is done with clip to MET then to LINE and the Ka rating is taken. The PSCC test is between LINE/NEUTRAL and the Ka is taken, which ever is the highest is the value you take. Note on a TNC-S the chances are thje values will be near enough the same.

Hi Malcolm,
can I just check 3 probe set up PEFC join earth and neutral probes then probe MET and line supply side. Then PSCC Neutral and earth probes joined, probe Line and Neutral supply side?

Cheers