calculating Zs with only R2 reading

[egginyourface]

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

 

[piggyitm]

Why be bothered if it's live or not?Your going to break a leg if you fall off regardless

 

[sparkiegaz]

get better access equipment , tower , a frame ladder etc,,,if your not happy working at height get someone else to do it,,,,,

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

 

[Sparky Ninja]

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

Yes it can be done.

Could you not still have done the R1&R2 tests?

 

[Sparky Ninja]

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

Technically carrying out R2 tests and calculating Zs values does still fall within the scope of BS7671.

 

[sparkiegaz]

might well do but im always gone down the road if i have a test equipment to take measurements use them,,,,maybe its the way ive been taught

Technically carrying out R2 tests and calculating Zs values does still fall within the scope of BS7671.

 

[SPARTYKUS]

Yes it can be done.

Could you not still have done the R1&R2 tests?

Widdler .... someone else has pointed this out, you're not calulating it though are you, you're guessing it!

egginyourface,Zs can be calculated when you have dead test results for R1+R2, and a Ze (either by measuring it, or enquiring from the supplier what they deem it to be).

you CANNOT calculate Zs without these things. You can guess it though but whats the point in that. If you cannot take the reading then note that, leave it with a line through, or a cross, don't put "LIM" unless you agreed not to measure it, do not guess

 

[PC Electrics]

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

I can't help wondering, if you were doing a PIR and you have the CU open anyway (must have to connect your wander lead to MET presumably) then was it really too much trouble to link out the line and earth and then carry out R1+R2. Also, if you're only measuring R2, how are you testing for (switch) polarity? Or is that a LIM?

The NIC do recommend against carrying out Zs at lights for H&S reasons. Personally I disagree with this at pendants and battens, but agree at fancy fittings. So at fancy fittings I generally do R2 to the casing.

 

[pushrod]

If you put your EFLI tester at the end of the circuit you are measuring it. If you do (R1+R2)+Ze you are calculating it.
If you have a measured value for R2 and then work out R1 from either ratio of conductor size or known length and resistance values you are still calculating it. Obviously it will not be the same as a measured value for various reasons. Also remember that Ze does not have to be measured it can be found by enquiry. I don't think i would want be the one to say to a fancy design engineer in his office calculating every thing before a cable is even on site "oh you are just guessing!"

 

[Sparky Ninja]

Widdler .... someone else has pointed this out, you're not calulating it though are you, you're guessing it!

No.

You are wrong.

 

[pushrod]

No.

You are wrong.

That sounds like the type of discussion that my wife has with me

 

[telectrix]

That sounds like the type of discussion that my wife has with me

not usually a discussion with me , just a statement of fact . " you are wrong because i say so". LOL.

 

[Sparky Ninja]

That sounds like the type of discussion that my wife has with me

I thought I'd try it out, it normally makes me shut up.

 

[SPARTYKUS]

ok, ok, calculating, maybe I should look its definition up (can't be bothered ).

Still won't ever catch me doing it that way.

Pushrod, I agree, if you have R2, then you can do a calculation to arrive at a figure. But I disagree with your comment about a fancy design engineer - that is not the scenario here I think. I think this is an "installation" that is being PIR'd so not a paper exercise in an office designing circuits where there are no unknowns.

Yes you could use 1.67 if you can see a bit of T+E at one end that's 2.5mm2, and again at 'tuther, but in all likelihood you will not be able to see what is inbetween.

As I'm sure you know from experience and horrors you've seen, nothing is ever perfect under floors, etc.

SO I would still maintain that doing it that way is an estimation. Not calculated, not in the same way you would calculate Zs when you have a measured R1+R2 and a measured or provided Ze.

So there.

 

[pushrod]

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

ok, ok, calculating, maybe I should look its definition up (can't be bothered ).

Still won't ever catch me doing it that way.

Pushrod, I agree, if you have R2, then you can do a calculation to arrive at a figure. But I disagree with your comment about a fancy design engineer - that is not the scenario here I think. I think this is an "installation" that is being PIR'd so not a paper exercise in an office designing circuits where there are no unknowns.


Yes you could use 1.67 if you can see a bit of T+E at one end that's 2.5mm2, and again at 'tuther, but in all likelihood you will not be able to see what is inbetween.

As I'm sure you know from experience and horrors you've seen, nothing is ever perfect under floors, etc.

SO I would still maintain that doing it that way is an estimation. Not calculated, not in the same way you would calculate Zs when you have a measured R1+R2 and a measured or provided Ze.

So there.

The original question is at the top - the answer is yes. Would it be the way you would choose to do it - quite probably no.

I did not say the design engineer was the scenario here, it was just an illustration that calculation is a valid method.

The words estimate and calculate have a considerable degree of overlap in meaning. Neither of them mean guess though - you are moving your goal posts here

 

[morph]

no it cant be done
if you dont have the R1 value you cant do it by measurement or otherwise
you cant calc R1 as you dont know the lenght