Zs - Ze

[driverman]

Hi guys, doing bit of revision here. What is the correct answer to give under exam conditions to this question? State why Ze-Zr cannot be used to accurately determine the value of R1 + R2? Could it be something to do with number of connections within the circuit under test, possibly a loose connection etc which would then give a higher Zs reading? I'm sure there must be a more obvious answer. Thanks

 

[Matt85]

I think you need to be looking down the lines of parallel paths mate

 

[Simonslimline]

Zs is taken with protective bonding connected to the MET so parallel paths may make the reading lower than Ze + (R1+R2)

 

[ian.settle1]

Hi guys, doing bit of revision here. What is the correct answer to give under exam conditions to this question? State why Ze-Zr cannot be used to accurately determine the value of R1 + R2? Could it be something to do with number of connections within the circuit under test, possibly a loose connection etc which would then give a higher Zs reading? I'm sure there must be a more obvious answer. Thanks

What's Zr when it's a home?

 

[bigdavs83]

It's an MG.

 

[driverman]

What's Zr when it's a home?

Well ..I did get the title right.....but well spotted!

 

[Silly Sausage]

What's Zr when it's a home?

It's a measurement that you're not sure about.

 

[SPARTYKUS]

Driverman

parallel paths can make an enormous difference to the final Zs. The difference of an order if the Ze is appalling (which it often is, TT wise).

so for example, you may get a Zs of 6.4 Ohms for a circuit with a Ze of 122 Ohms and an R1+R2 of 0.67 Ohms.

how could Zs - Ze ever be a useful measurement, except in how useless it might be....do you see from the example above?

the bonds to the water pipe and gas pipe in the example above massively reduce the Zs.


In fact, some properties that are TT can happen to be connected via a water main to another nearby property that is TN.... Thus producing even more incredulous results (like a Ze at the earth rod of say, 34 Ohms but the socket circuit reads 0.34 Ohms for its Zs).

s.