Quote:
Originally Posted by treelectric  yes, I do see what you mean, but my old meter gives me Z between live and phase, as well as Ze so usually just calculate it. Maybe on the next try I'll use the meter they supply as I noted it did pscc and pefc.
Do you need Zs at the actual sub board? Or do you put the Ze for the main board into the schedule of test results for the 2nd board? To me it would seem much more logical to take another Ze at the sub board, as you could in a real situation have a long run of cable between the two, and that could make a significant difference to disconnection times. And for the sub main, the connection cable between the two would be part of the external
impedance loop. Am I right?
And thanks again. |
Ok,
your meter actually measures Z anyway, so if you connect it line to Earth its Ze, line to neutral would be Z. And meters measuring PFC's do the same, between line and earth its PEFC and line and neutral its PSCC
now for the submain, take your measurement, but wether its Ze or Zs its the same reading at the point! Your Ze is only the external EFLI, and we disconnect the incoming earth so we are ONLY reading that part of the circuit which is external.
Now if you wanted to measure Ze at the sub board, you wouldnt disconnect the incoming earth to the suboard, and even if you did, you would still get parralel paths through your main and supplementary bonds etc etc.
And it wouldnt be Ze because its not external to the installation, because it includes R1+R2 of the submain. So actually when you measure the incoming to the sub board, you are measuring Ze + (R1+R2) , which of course is Zs!!!
and of course, the disconnection times (through the Zs measured at the submain circuits) ALREADY includes 'true' Ze + (R1+R2 submain) + (R1+R2 particular submain final circuit)
So, on both of your schedules of test results it is acceptable to put the same value of Ze (because you will only have one value of Ze)
although it is also acceptable to include R1+R2 (and the Zs value) of the submain cable as if it was another final circuit
i always tell people: its YOUR paperwork, and as long as you explain what you have entered, and it is logical, then you cant (or shouldnt ) be criticised for it
hey this getting good aint it!!!
