calculating Zs with only R2 reading

[egginyourface]

is it possible to calculate zs by only using r2 + ze reading??

 

[bugsy]

Nope not unless you a - no I won't say it

 

[ste mac]

Yes it is possible, but how can you be certain that the Zs is correct unless you actually test R1, R2 & Ze. Why don't you have a Zs measurement or all the required measurements to calculate Zs?

 

[morph]

not poss with just R2 and ZE

 

[telectrix]

you can get R1 from R2. ( for 2.5/1.5mm, R1=R2/1.67) but better by far to measure Zs.

 

[morph]

you can get R1 from R2. ( for 2.5/1.5mm, R1=R2/1.67) but better by far to measure Zs.

mathmaticaly yes , but that aint going to be the actual reading of R1 , in a lighting circuit the resitance of the line conductor could be greater than the resistance of cpc

 

[telectrix]

true. but nearest without measurement. can't see why R1+R2 can't be measured.

 

[Sparky Ninja]

Yes you can, you will need to know the circuit length and the size of the conductors.

 

[SPARTYKUS]

egginyourface

is that a wind up?

 

[morph]

could be very different with two way circuit,

 

[morph]

Yes you can, you will need to know the circuit length and the size of the conductors.

dont work like like that, too many unknown extra resistances in switches and terminations that will not be included in your calcs

 

[Sparky Ninja]

dont work like like that, too many unknown extra resistances in switches and terminations that will not be included in your calcs

your observation whilst partly true, is irrelevant. Zs can be obtained by calculation or measurement. The title of this thread is 'Calculating Zs with only R2 reading'.

You can't let your opinions cast a shadow over the facts.

 

[PC Electrics]

One cannot calculate Zs when all one knows is Ze and R2, unless you can be certain of the R1/R2 ratio for the circuit (eg a 6/2.5 radial supplying a cooker).
However, for other circuit types you can estimate Zs. For lighting circuits and heating control circuits I generally estimate Zs = Ze + 3R2. I also state on any report or cert that this is an estimate.
Usually though, the purpose of measuring R2 is to prove cpc continuity and calculating or estimating Zs from this is unnecessary.

 

[sparkiegaz]

you have a tester for a reason do the job right or not at all.....

 

[egginyourface]

sooooo no it cant be done and or yes it can b

the reason i ask is did a periodic today and only did r2 on lighting circuits. Dont like doing zs on lighting points as i dont like live testing from high up on a ladder