Zs revision

[searley]

has anybody out there got anygood revision for zs calcs IE using the rule of thumb 0.8 method need to do calcs and no if they pass or fail the values. headbang

thanks for looking.

 

[Robin Spark]

Hi Searley,

think I am having a Leffe Blond moment cos not sure what exactly you are asking for?

 

[Bez]

Me neither, if you look at the values in BRB Page 49. Multiply them by 0.8, that will give you the corrected value. You can double check yourself on page 103 of the OSG.

I take it this is what you're looking for.

Bez

 

[SPECIAL LOCATION]

has anybody out there got anygood revision for zs calcs IE using the rule of thumb 0.8 method need to do calcs and no if they pass or fail the values. headbang thanks for looking.

Ahhh Another Classic Searley question? :x

Is this any help m8? ?:| :|

The maximum permissible earth fault loop impedance values are those given in the tables 41.2 / 41.3 /41.4 on pages 48 & 49 of Big Red.

IF the values are exceeded whilst the cable is at NORMAL OPERATING TEMPERATURE it is a FAIL.

Either need lower rated protective device OR larger CSA cable.

IF you are doing your tests with cables that are cooler than normal operating temperature (which is ALL of the time cuz you test while the circuit is not under full load, or dead if doing R1+R2+Ze!) THEN you need to take pay attention to the note below each table... that references to the guidance in Appendix 14 Page 361 of Big red.

Appendix 14 suggest the '0.8 x Max tabulated value' as being a good "rule of thumb" to a safe "Cold" reading that will still meet 411.4.5 or 411.5.4 when the cables are warmer under "normal operating conditions".

So any recored value lower than the "0.8 Thumb value" will be a good 'PASS'

HOWEVER a reading higher than the 0.8 Rule-of-thumb and Lower than the tabulated max values can still be a Pass, but you would just need to do a more precise assesment...

see bottom few paragraphs of Page 361...

AND take a point of the final NOTE

"other methods are not precluded"

Bottom line

Below 0.8 x Max permissible = Pass

Above 0.8 And below max permissible may be Pass or Fail depending upon other calcs!

Above max permissible = Fail

SL

GuinnessGuinnessGuinness

 

[SPECIAL LOCATION]

Hi Searley,think I am having a Leffe Blond moment cos not sure what exactly you are asking for?

a Leffe Blond moment ...... :|

a Leffe Blond moment ....... ?:|

a Leffe Blond moment ........

I am sure thats what Apache & Badger used to call....

A Deke's Red Dress Moment!

or am i getting confused again???Blushing

:coat :coat

 

[Risteard]

IF you are doing your tests with cables that are cooler than normal operating temperature (which is ALL of the time cuz you test while the circuit is dead!)

Without any load connected to the circuit, but not dead. It is, after all, a live test.

The 1.2 factor could also be applied to the (R1+R2) value for the circuit (subtract Ze), assuming that the temperature is 20 degrees or corrected to 20 degrees first. Add Ze to the corrected (R1+R2) and then this can be compared with the tabulated value in BS7671:2008.

Obviously the 0.8 "Rule of Thumb" is the simpler of the two methods.

 

[SPECIAL LOCATION]

Without any load connected to the circuit, but not dead. It is, after all, a live test.The 1.2 factor could also be applied to the (R1+R2) value for the circuit (subtract Ze), assuming that the temperature is 20 degrees or corrected to 20 degrees first. Add Ze to the corrected (R1+R2) and then this can be compared with the tabulated value in BS7671:2008.

Obviously the 0.8 "Rule of Thumb" is the simpler of the two methods.

Quite correct Ristard....

too many GuinnessGuinnessGuinness

& past midnight...

me brain knew what i meant...

just me fingers didn't keep up! :_| :x

I shall go and correct now...

DOH!!!Blushing

 

[Risteard]

too many GuinnessGuinnessGuinness

Good man! It happens to the best of us at times! ROTFWL Guinness :Y

 

[searley]

hi this is what i was getting at just did`nt no how to scan it and get it on here.

i no they are 16th edition questions but it was to try and give us an idea how it worked do they look good to you pro`s out there.

 

[Bez]

Careful with the use of the < symbol in your answers, had to do a double take on some of them.

 

[searley]

where they all right as i have nothing to check them off ?

 

[Bez]

Will check them for you when next online. Off to watch Jordan in the Jungle Now:^OGuinness

 

[batty]

Will check them for you when next online. Off to watch Jordan in the Jungle Now:^OGuinness

Is Peter back as well.

 

[Bez]

where they all right as i have nothing to check them off ?

Example reads wrong to me, unless i'm missing something it should read:

10.2 ohm(measured value) < 14.16 ohm (corrected vaue) PASS

 

[searley]

are my calcs right for these on question 26 ?

1, 2.3 X 0.8 = 1.84 fail

2, 1.44 x 0.8 = 0.72 pass

3, 0.57 x 0.8 = 0.456 fail

4, 0.36 x 0.8 = 0.288 pass

thanks for looking.

 

[Bez]

are my calcs right for these on question 26 ?1, 2.3 X 0.8 = 1.84 fail

2, 1.44 x 0.8 = 0.72 pass

3, 0.57 x 0.8 = 0.456 fail

4, 0.36 x 0.8 = 0.288 pass

thanks for looking.

Multiplication error on No. 2 1.44 x 0.8 = 1.15

Other than that your calcs are fine but your passes and fails are back to front.

Don't forget as long as your measured value is below the corrected value, it's a pass.

Hope this helps