Prospective fault current

[EastAnglian]

Uksel - Just as the Nominal Voltage is oscillating then so is the Current - that's why its called "Alternating Current" as it flows in opposite directions each half cycle. It is therefore just as valid to describe the nominal voltage of the UK supply as 230V RMS as it is to refer to an alternating current of 100A RMS.

When using Ohms law to calculate an AC current flowing in a load as a result of an AC Voltage we replace "Resistance" by "Impedance". Impedance is a complex resistance which is related to how the load responds to an alternating current. The load's capacitance and inductance as well as resistance all contribute to its impedance. As capacitive and inductive reactance are related to the frequency of the alternating current/voltage then there can be a frequency dependence on the equation.

For PFC we assume that at 50Hz the impedance of the source (ie Ze) is a simple resistive value.

So Ipfc=Uo/Ze

 

[darran]

you need to disconnect the main incomming earth for a Ze test to eliminate the parallel earth paths, but the PFC (PEFC, PSCC) is carried out with the bonding in place.

 

[cornburn]

Uksel - Just as the Nominal Voltage is oscillating then so is the Current - that's why its called "Alternating Current" as it flows in opposite directions each half cycle. It is therefore just as valid to describe the nominal voltage of the UK supply as 230V RMS as it is to refer to an alternating current of 100A RMS.

When using Ohms law to calculate an AC current flowing in a load as a result of an AC Voltage we replace "Resistance" by "Impedance". Impedance is a complex resistance which is related to how the load responds to an alternating current. The load's capacitance and inductance as well as resistance all contribute to its impedance. As capacitive and inductive reactance are related to the frequency of the alternating current/voltage then there can be a frequency dependence on the equation.

For PFC we assume that at 50Hz the impedance of the source (ie Ze) is a simple resistive value.

So Ipfc=Uo/Ze

Thread is 18 months old, 1-0 to me

 

[adasadas]

Fellas. I thought a PFC was measured with the main earth still connected to the installation, line to earth, and a PSC line to neutral; only with a Ze do you disconnect the earth..

Fellas. I thought a PFC was measured with the main earth still connected to the installation, line to earth, and a PSC line to neutral; only with a Ze do you disconnect the earth..

 

[jamie-spark]

Disconect Main Earth. Put meter across Earth incoming (met) Connect other leads to Phase conductors do test. Then connect Earth and Neutral test leads together and connect to neutral phase conductor, connect the other lead to Line Phase conductor.
Test again. Wich ever is the highest reading in Ka record that on the test results.
Don't forget to re connect the main Met.
All these tests done with power on cons unit OFF

This is a Ze you are doing a pfc Should be done with all earths and bonds connected as more paths to earth may mean a greater fault current as there is less resistance. Then test between line and N and take the highest amount. if you dont have that function do a loop test take the reading and divide 230 by the result. ie 230/ 0.26 = ka =0.884 ( 884 amps)

 

[Fred West]

Well I was going to offer him this

[ame=http://www.youtube.com/watch?v=54C_FLSZaCY&feature=relate]YouTube - Prospective short circuit current test[/ame]

But then I noticed the date he asked,if he has not found out by now he has no hope

 

[trebor]

can somone tell me how to mesure pfc for a domestic property need this asap!!!!!
thanks in advance

Set meter on pfc

1 test between incoming line and neutral = PSCC

2 test between incoming line and the earth bar with all earths connected to include all parallel earth paths, not disconnected as suggested = PEFC

highest of 2 is recorded as pfc

can somone tell me how to mesure pfc for a domestic property need this asap!!!!!
thanks in advance

Set meter on pfc

1 test between incoming line and neutral = PSCC

2 test between incoming line and the earth bar with all earths connected to include all parallel earth paths, not disconnected as suggested = PEFC

highest of 2 is recorded as pfc


NB only Ze is measured with the main earth disconnected and installation isolated

 

[Guest123]

I'm hoping the OP has finished his test cert by now.......the thread is 18 months old.

 

[jamie-spark]

Aye better late than never

 

[tonynulty]

Thanks Laney06, never done it this way before, always used tester, how do you know this is correct, if it is this is easier and saves the cost of a loop impedance tester. tony

 

[laney06]

Hi there. This is a calculation to comfirm your readings are correct. You still need to measure.

Ps. You'd still need a loop testerto get your ze figure.

 

[brucelee]

am guessing parallel paths???

you dont disconnect earthing conductor for pfc

 

[HIGHERLANE]

I have my niceic inspection tomorrow and would like to know how to calculate your cable length from the results you have measured on the cert? Can you help

 

[Guest123]

I have my niceic inspection tomorrow and would like to know how to calculate your cable length from the results you have measured on the cert? Can you help

Probably the easiest way is to use your R1+R2 values and the stated values of resistance per metre for a particular cable, found in the OSG for instance.

 

[brucelee]

Length = Resistance x 1000 divided by m/ohm/m for the csa of the conductor(s)