Quick question that come up in college

[AshFR]

Hi all. Just a quick question that come up in college. Why is the r1+r2 values lower than the Zs on the same circuit?

Example: Cooker Circuit - R1+R2 = 0.4ohm, Zs = 0.6ohm

Why is the Zs higher than the R1+R2?#

Thanks.

 

[telectrix]

because Zs=(R1+R2) + Ze

 

[AshFR]

because Zs=(R1+R2) + Ze

Thats it! Thank alot. Is this the Ze at origin or Ze on that circuit?

 

[Deleted member 26818]

Z stands for impedance.
Ze is the impedance external to the installation.
Zs is the total impedance from source, up to the point of measurement.
As such Ze is measured at the origin of the installation, Zs is measured along whichever circuit you are testing, and the highest reading is recorded as being Zs for that circuit.
It should be noted, that Ze is measured with parallel earth paths such as Protective Bonding Conductors disconnected.

 

[AshFR]

Ok well looking at some test results from a few years back, it says Ze at origin is 0.13ohm and cooker circuit r1+r2 = 0.4ohm and Zs = 0.6ohm

How did they get Zs at 0.6ohm when r1+r2 (0.4) + ze (0.16) is 0.56?

 

[telectrix]

you will get some effect from parallel paths that will give a lower Zs than expected. but also the internal components of MCBs etc. may give you a higher value.

 

[AshFR]

Awesome. Thank you very much. Really need to freshen up on my inspecting and testing as i hoping ive got my AM2 in a few months.

 

[Deleted member 26818]

Every joint or connection can introduce a resistance.
Also there is a slight difference between resistance and impedance, with impedance being slightly higher than resistance, as impedance involves both resistance, and reactance (capacitive and inductive).

 

[kev123]

Awesome. Thank you very much. Really need to freshen up on my inspecting and testing as i hoping ive got my AM2 in a few months.

Dude, get your head in your books and get learning. You should really know if you are approaching the AM2 exam what the formulae Zs=(R1+R2) + Ze stands for.