Help, why can`t you use Zs - Ze to accurately determine the value of R1 and R2

[carshalton]

Why can`t you use Zs - Ze to accurately determine the value of R1 and R2

Thanks

 

[Andy™]

because Zs includes parallel paths

 

[ianmacd]

Zs-Zdb should be more realistic though.

 

[Andy™]

Zs-Zdb should be more realistic though.

for most circuits, yes. but not for circuits with a combi, shower etc

 

[ADS]

Hi mate,

Z is the 'impedance' of the conductors in an AC circuit and is reliant on a number of factors. (measured live)

R is the resistance of a conductor - (normally a DC measurement whilst circuit is dead)

If you google 'impedance' you will immediately realise the difference between the two.

It therefore stands to reason that if you take one 'impedance' (Ze) from another 'impedance' (Zs), your answer cannot possibly be a 'resistance' (R1+R2)

Your answer will be another Z or 'impedance' - the difference between Zs and Ze.

 

[carshalton]

Thanks Everyone for your Help

Alan ..

 

[JUD]

Hi mate,Z is the 'impedance' of the conductors in an AC circuit and is reliant on a number of factors. (measured live)

R is the resistance of a conductor - (normally a DC measurement whilst circuit is dead)

If you google 'impedance' you will immediately realise the difference between the two.

It therefore stands to reason that if you take one 'impedance' (Ze) from another 'impedance' (Zs), your answer cannot possibly be a 'resistance' (R1+R2)

Your answer will be another Z or 'impedance' - the difference between Zs and Ze.

So how do you explain Zs = Ze + (R1 + R2)

 

[sparkytim]

NICEIC Test and Inspection book Page 251

"For circuits rated up to about 100 A, in which the line and cpc conductors are part of the same wiring system or immediatly adjacent to each other and not separated by ferrous material the ac impedance is not signficantly greater then the dc resistance" In such case R1+R2 is approximately equal to Z1+Z2 and the use of a test instrument supplying a dc test current will generally be sufficent"

ut the kettle on

 

[ADS]

So how do you explain Zs = Ze + (R1 + R2)

It is an allowable calculation as an approximation of Zs, if it isn't possible to measure the actual Zs.

It is allowed because of what 'Tim' states here:

"For circuits rated up to about 100 A, in which the line and cpc conductors are part of the same wiring system or immediatly adjacent to each other and not separated by ferrous material the ac impedance is not signficantly greater then the dc resistance" In such case R1+R2 is approximately equal to Z1+Z2 and the use of a test instrument supplying a dc test current will generally be sufficent"

R1 + R2, though, should be a measure of conductor resistance only so, if you add what I said, to what 'Andy' said earlier:

[quote name='Andy