Zs=ze+r1+r2

[Cj24]

Hi, i did my practical 2391 last week and I have looked at my zs results and this formula doesn't seem to work out right for any off my results, obv ze is measured at the origin so that staying the same in all my calcs but wen u add the r1+r2 it doesn't match my recorded zs result, was there something I was doin wrong

 

[Guest123]

The equation Zs = Ze+(R1+R2), does not always compute as more often than not measured Zs results include any parallel paths that may be present via bonding conductors, structural steelwork, steel containment etc etc.

More often than not, a measured result will be lower than a calculated one due to these parallel paths.

 

[miner69er]

No there is nothing you have done wrong, the Zs will hardly ever correspond with the Ze+(R1+R2) as you have things like parallel paths on Zs which generally make the measurment lower. Also things like the circuit breaker creating a resistance which you didn't have in line when testing Ze or R1+R2. Little things like this make the theoretical values different to what you will actually measure.

beat me too it lenny, the fairys don't keep moving your letters like my keyboard!!

 

[Guest123]

beat me too it lenny, the fairys don't keep moving your letters like my keyboard!!

No, I have toshiba's new anti fairy keyboard software.:wacko:

 

[dingledong]

where can you buy the toshiba anti fairy keyboard software it seems like a must have

 

[SPARTYKUS]

At the risk of sounding like an elitist arse, cj24, you should really know that kind of thing inside out if you're taking the 2391 ..... sorry .... good luck with it anyway fellow.

 

[Cj24]

I do know these things really but wen reading through all my notes u start to look bit deeper into things then question things n it's nice just for confirmation

 

[telectrix]

well, if you put r1 instead of R1 on a 2391 exam paper, it will be "nil pwants" as they used to say in the eurinevision pong contest

 

[cliffed]

surely the formulae must work,its te basic of most calculations.Parrallel earths should not enter the equation,if disconnected from the db & tested. ta ra bab

No there is nothing you have done wrong, the Zs will hardly ever correspond with the Ze+(R1+R2) as you have things like parallel paths on Zs which generally make the measurment lower. Also things like the circuit breaker creating a resistance which you didn't have in line when testing Ze or R1+R2. Little things like this make the theoretical values different to what you will actually measure.

beat me too it lenny, the fairys don't keep moving your letters like my keyboard!!

 

[malcolmsanford]

surely the formulae must work,its te basic of most calculations.Parrallel earths should not enter the equation,if disconnected from the db & tested. ta ra bab

The formula will only work if your doing the R1+R2 as a dead test with as you say the conductors disconnected.

Often in a PIR a Zs will be done by measurement as a live test and will have parallel paths.

Wait now for the NICEIC to condemn me for working live

 

[telectrix]

better to work live. you can't work when you're dead.

 

[Cj24]

Can someone just explain in idiot form for me, the diff between r1+r2 and R1+R2, I have already asked but can't find where I asked now n I keep gettin told diff things, some peeps say there exactly the same but I'm sure there not, is r1+r2 your actual reading at the socket wen u have crossed phase n CPC at board? And is R1+R2 your actual end to end reading obv phase to phase and CPC to CPC,

 

[mark80]

R1 + R2 is the reading between line and cpc in a circuit.
r1 is the resistance of the line conductors in an end to end test of a RFC. r2 is the cpc resistance and rn is the neutral resistance.