Spot the mistakes - Billy Bulls**t circuit sheets i think

[rallyandy]

I went to look at a hotel today, the first thing is the old boards which have various gaps and 3Ka breakers JB's everywhere, and look at the recorded results !!

 

[Deleted member 26818]

Looks like only the Zs for the socket circuits were actually tested, the rest calculated.

 

[rallyandy]

thats what i thought as well, look at the second socket circuit the Zs reading is higher than the R1 + R2 reading

 

[telectrix]

how doi enlarge the pic big enough to read it? i can just read "circuit details" , but none of the entries.

 

[Deleted member 26818]

Left click on the image, then you should get a magnifying glass with a + in it.
Remember to back page, rather than close the window, otherwise you'll close the browser.

 

[rallyandy]

how doi enlarge the pic big enough to read it? i can just read "circuit details" , but none of the entries.

I think if you just hover the mouse pointer over the pictures they automatically expand

 

[Deleted member 26818]

thats what i thought as well, look at the second socket circuit the Zs reading is higher than the R1 + R2 reading

You often find that Zs is higher than R1 + R2. Remember Zs = Ze + R1 + R2.

 

[rallyandy]

You often find that Zs is higher than R1 + R2. Remember Zs = Ze + R1 + R2.

sorry spin i posted that wrong lol the R1 + R2 is higher than the Zs reading

 

[Deleted member 26818]

sorry spin i posted that wrong lol the R1 + R2 is higher than the Zs reading

That happens quite a lot as well, parallel earth paths. Especially with metal conduit.

 

[telectrix]

Left click on the image, then you should get a magnifying glass with a + in it.
Remember to back page, rather than close the window, otherwise you'll close the browser.

thanks for that. it works. remember not to employ me for anything to do with computers, esp. software. LOL.

 

[rallyandy]

That happens quite a lot as well, parallel earth paths. especially with metal conduit.

its all wired in T&E, radials to all the rooms

 

[eskimo39]

I have seen this quite a lot. They used to say that you were not allowed to do a ZS reading at any point other than a socket due to the exposure of live parts (with a socket you can use a plug top tester) so the only way to get a Zs was (R1+R2)+Ze, the R1+R2 that is lower than the Zs is most likely due to a parallel earth path (eg bonding) and as this was the only real test, shows in the results. Not sure what the norm is in regards to Zs testing now, I just throw the covers off and get in their with my tester.

 

[rallyandy]

I have seen this quite a lot. They used to say that you were not allowed to do a ZS reading at any point other than a socket due to the exposure of live parts (with a socket you can use a plug top tester) so the only way to get a Zs was (R1+R2)+Ze, the R1+R2 that is lower than the Zs is most likely due to a parallel earth path (eg bonding) and as this was the only real test, shows in the results. Not sure what the norm is in regards to Zs testing now, I just throw the covers off and get in their with my tester.

i was thinking on the lines that they would have stayed with one method of testing the circuitsi, ie all the rooms have one 2.5 T&E radial for one socket and one 1.0 T&E for lighting, so surely if the Ze is recorded as 0.09 then for instance if you add the R1 + R2 of 0.71 the Zs should be 0.8 ? or is it me being a bit dumb lol

 

[telectrix]

by calculation, you are correct, but due to parallel paths (water pipes etc.) to earth, the Zs can be lower than calculated. this is most noticeable in TT systems where the resistance to earth through services is less than the resistance through the earth rod.

 

[rallyandy]

by calculation, you are correct, but due to parallel paths (water pipes etc.) to earth, the Zs can be lower than calculated. this is most noticeable in TT systems where the resistance to earth through services is less than the resistance through the earth rod.

it just didn't look right to me, this is just one sheet of many for the various boards around the Hotel and they all vary, i just thought the results would be similar on the other boards and circuits if there were parallel earth paths, plus i looked for supplementary bonding but couldn,t find any only main bonding so far, ( I must be on a bad day lol) and its TNS

 

[IQ Electrical]

by calculation, you are correct, but due to parallel paths (water pipes etc.) to earth, the Zs can be lower than calculated. this is most noticeable in TT systems where the resistance to earth through services is less than the resistance through the earth rod.

This is why the Zs-Ze = (R1+R2) formula should never be used as it makes no allowance for the parallel paths that exist in all but the most basic of 'all-insulated' installations.

 

[telectrix]

take a few readings and compare with them. that should give an idea.

 

[rallyandy]

i,m back ther tomorrow so will start taking my own readings, i was going off the existing readings today for an overview of the existing installation

 

[rallyandy]

i think i need to review my test procedures , i have always measured Ze at the supply incomer, then R1 + R2 and added them together obviously not allowing for parallel earths, you learn something new every day on here and i dont mind admitting it

 

[telectrix]

i always measure Zs unless by doing so i might create danger for myself or others. to give an idea of the effect of parallel paths, measure Ze as normal with the main earth dissed. then measure again with it connected. you should find the 2nd reading is lower.