impedance values

[johnnyjb]

Hi im a small bit confused about finding the values of the loop impedance of an installation. I fully understand the path of the loop and all that but im stuck on the temperature factors to be applied.

If you use a loop impedance tester , is the value displayed the correct value or do you need to apply a temperature corection factor as the cable will most likely not be at its highest temperature capability i.e 70 degrees. Or does this method only apply when manually measuring the impedances

Sorry if i confused anyone

 

[GaryMo]

Measured figures will need to be compared against a corrected figure of 80% of the maximum values from BS7671.
If your measured value exceeds 80% of the maximum value of earth fault loop impedance then a more precise assessment will need to be made.

See Appendix 14, BS7671:2008 for more information.

 

[johnnyjb]

Is it that if theloop tester gives a reading over 80 percent than a more precise measurement needs to be done or is it over 80 if manually measured

 

[ban-all-sheds]

Is it that if theloop tester gives a reading over 80 percent than a more precise measurement needs to be done or is it over 80 if manually measured

Using a loop tester is a manual measurement, and it displays what it measures.

 

[GaryMo]

There's two methods of gaining a Zs value - calculation from Ze+(R1+R2) or 'manual' measurement with an earth fault loop impedance tester.
The values in both instances should be compared to 80% of the values in BS7671, if either give a figure over 80% that of the maximum allowed under BS7671 then a more precise assessment should be made.

 

[johnnyjb]

Ban All sheds as usual being snotty , not answering a question and trying to humiliate a poster.

If you went to the effort of replying why didnt you answer the question instead of pointing out how badly the post was worded.Too much free time

 

[flyingsparks]

Ban All sheds as usual being snotty , not answering a question and trying to humiliate a poster.

If you went to the effort of replying why didnt you answer the question instead of pointing out how badly the post was worded.Too much free time

He is an arrogant know it all....

 

[RF Lighting]

....who posts only correct information based on what we are given. It made perfect sense to me.

We are not mind readers you know.

 

[FingRinal]

Using a loop tester is a manual measurement, and it displays what it measures.

A loop tester might be manually operated but it measures and calculates Zs automatically

And it doesn't display what it measures. It displays what it calculates after measuring something else i.e. not Zs

 

[securespark]

....who posts only correct information based on what we are given. It made perfect sense to me.

We are not mind readers you know.

I want to second that. I don't think he was doing any of that which he is accused.

As I understand it, the OP wanted to know if the figure displayed was corrected or not.

 

[oharaf]

BAS was only providing clarification, 'manual' meaning by hand, means use your tester or your fingers.

However only one will provide an accurate measurement the other will bloody well hurt!!!

 

[johnnyjb]

This forum is good but some arrogant know alls surface now and again and think that their post count in their profile allows them the right to be smart and it really annoy me.

This is getting off topic.

 

[ban-all-sheds]

A loop tester might be manually operated but it measures and calculates Zs automatically

And it doesn't display what it measures. It displays what it calculates after measuring something else i.e. not Zs

True - what I meant, in the context of the original Q:

If you use a loop impedance tester , is the value displayed the correct value or do you need to apply a temperature corection factor as the cable will most likely not be at its highest temperature capability i.e 70 degrees. Or does this method only apply when manually measuring the impedances

was that using a loop tester is just as much a manual operation as measuring R1+R2 with a low-range ohm meter and adding that to a by-enquiry-Ze, and that what it displays is based entirely on what it measures - the instrument does not apply any temperature correction factors...

 

[FingRinal]

A loop tester might be manually operated but it measures and calculates Zs automatically

And it doesn't display what it measures. It displays what it calculates after measuring something else i.e. not Zs

True - what I meant, in the context of the original Q:

If you use a loop impedance tester , is the value displayed the correct value or do you need to apply a temperature corection factor as the cable will most likely not be at its highest temperature capability i.e 70 degrees. Or does this method only apply when manually measuring the impedances

was that using a loop tester is just as much a manual operation as measuring R1+R2 with a low-range ohm meter and adding that to a by-enquiry-Ze, and that what it displays is based entirely on what it measures - the instrument does not apply any temperature correction factors...

Perhaps if you'd put it like that in the first place, JB wouldn't have taken offence. And if you did mean that, then you should have known that he was asking the question as regards the application of the 80% rule of thumb and you should have answered that.

I understood his question to mean that a 'manual' measurement involved taking low resistance measurements (of R1 and R2) and adding them to declared Ze rather than using a loop tester to 'automatically' (in one go) measure Zs. And to ask if the 80% rule of thumb applied to both or just one of them.