Relationship ze and pfc

[Kyle_Trainee]

So I’m currently studying Ze and pfc etc kind of understanding it.
main question really is about the relationship between them both I understand that the lower the Ze the higher the fault current but why is this? Is it just simply to do with ohms law? And I’m just over thinking and confusing myself

Any responses would be appreciated

 

[DPG]

So I’m currently studying Ze and pfc etc kind of understanding it.
main question really is about the relationship between them both I understand that the lower the Ze the higher the fault current but why is this? Is it just simply to do with ohms law? And I’m just over thinking and confusing myself

Any responses would be appreciated

A lower loop impedance allows more current to flow, and yes this is Ohms law.

Think of what happens when each variable is changed, either up or down. Example - what would happen to the PFC figure if the supply voltage was higher?

 

[StephenRowley]

Is it just simply to do with ohms law? And I’m just over thinking and confusing myself

Yeap pretty much simple ohms law.

 

[Kyle_Trainee]

A lower loop impedance allows more current to flow, and yes this is Ohms law.

Think of what happens when each variable is changed, either up or down. Example - what would happen to the PFC figure if the supply voltage was higher?

the PFC value would increase?

 

[Deleted account]

You’ve got

amps pfc

ohms Ze

volts 230V

simple ohms law.

if pfc is 2.3 Ka and voltage is 230. What’s the Ze?

made it easy!

 

[Kyle_Trainee]

You’ve got

amps pfc

ohms Ze

volts 230V

simple ohms law.

if pfc is 2.3 Ka and voltage is 230. What’s the Ze?

made it easy!

so voltage/current so the resistance would be 0.1

 

[pc1966]

For a single phase domestic supply, where Ze/Zs is dominated by the cable resistance, it is just Ohm's law:

PFC = U / Ze

Typically your MFT reports both the PFC and Ze when measured, the PFC is based on the measured voltage U, but Ze is independent of that. You would use Ze along with R1+R2 (or Zs at the end of a circuit) to check that any over-current protection will disconnect fast enough for safety even at the lowest likely supply voltage.

The worst case PFC (of both earth-fault 'PEFC' and supply short-circuit 'PSCC' ) would be used to check that any over-current protection is able to safely interrupt any fault.

For three-phase and/or high current systems it gets more complicated, but the same basic principles apply. The IET's "Electrical Installation Design Guide" has some examples of the slightly more tricky cases on pages 76-81

 

[Deleted account]

so voltage/current so the resistance would be 0.1

Brill. It’s as simple as that.

 

[Mike Johnson]

When I was at school it was simply I=V/R ? it just seems as though its change for change sake. ?

 

[Julie.]

It's most certainly changed then, when I was at school it was V = IR

Looks like they have changed it all around.

Have to watch carefully, I have no doubt that they will change it again in the future to R = V/I or something.

 

[DPG]

It's most certainly changed then, when I was at school it was V = IR

Looks like they have changed it all around.

Have to watch carefully, I have no doubt that they will change it again in the future to R = V/I or something.

It's the bloody EU I expect.

 

[Mike Johnson]

It's a long time since I was at school, but isn't I = V/R the same as V = IR something like transposing one of the divisors to the other side of the resultant make it a multiplicand rather than a divisor?

 

[DPG]

It's a long time since I was at school, but isn't I = V/R the same as V = IR something like transposing one of the divisors to the other side of the resultant make it a multiplicand rather than a divisor?

It is indeed. I think they were joking though.

 

[Mike Johnson]

Then they should have put a emoji on it so this old man would know. ?

 

[Lister1987]

Probably buried in the multipart IEC 60050 series Electrical engineering vocabulary