R1+R2 will invariably involve one or both conductors being unterminated at the CU in order to join them together. Assuming a typical lighting circuit, loop in - out either at light fittings or switches, or a typical socket circuit, ring or radial. I fail to see how you are going to get much of an R1+R2 anywhere without having the accessories second fixed. Prior to that they are just a lot of cable ends sticking out of back boxes. It sounds like a lot of wasted work to join all the cable ends up to do some readings, then disconnect them again to 2nd fix.
You might want to confirm that you have 'continuity' where there should be continuity - and Insulation Resistance where there should be Insulation Resistance.....................before the plasterers come in and board it all.
I disagree with the 'sticking to the facts' and 'only say what's written in the Regs' - if he wanted that, he can find the answer in the Regs.
Said the man who was leaving the forum and never coming back in November!You might want to confirm that you have 'continuity' where there should be continuity - and Insulation Resistance where there should be Insulation Resistance.....................before the plasterers come in and board it all.
You might think I'm stating the obvious here, but what I mean is it is ONLY R1 + R2 - nothing else...............it shouldn't include things like earthed 'exposed conductive parts' - for example steel conduit or cable tray (unless specifically designed as the CPC for the circuit), so the measurement would be taken before 2nd fix, before all the little 'flyleads' etc are connected up - otherwise, why bother measuring it at all?
Calculating Zs will tell you that your 'disconnection times' should or shouldn't be met - measuring Zs will tell you that they will or they won't........a huge difference, and that is a fact.
as opposed to measuring it will?
Said the man who was leaving the forum and never coming back in November!Not necessarily.
I guess that was something else you misinterpreted?
I thought I'd give people the benefit of the doubt - shouldn't have bothered......... If I said the 'Neutral' was classed as a 'live' conductor, there are some on here who would argue the toss.
Cable tray = exposed conductive part! :Chmm?
Depends how you read my statement - maybe I should have put a comma after 'conduit'............but there again, it's ADS, so lets be picky......you know very well what my point was!
Measuring Zs will include all your bondings and exposed conductive parts etc...
Yes, but if you are determining Zs - and the definition of Zs includes parallel paths - then those things should be included in your result...........otherwise, you haven't got the figure for Zs, you've got the figure for Ze + R1 + R2.
that you are so anxious to avoid in you R1+R2 bit...
I'm not anxious to avoid them........but again, if you are going to measure R1 + R2, then measure it! - Don't measure it with all kinds of parallel paths and then call it R1 + R2.....because it's not!
But if they happen to become disconnected, because the plumber chops off an earth wire, may result in Zs not meeting the requirements of Chapter 41!
Maybe, and if your auntie had b**ls, she'd be your uncle.
Whereas the R1+R2+Ze will be just the Earth fault loop impedance path as described in 2.7.14 of Guidance Note 3.
Yes, your right.........calculation will confirm the resistance/impedance of your Earth fault loop path.....but it won't confirm that there actually is a path!
What if the installer has inadvertently clamped down on a bit of the sheath/insulation, instead of copper, when re-terminating the CPC, after measuring R1 + R2........your calculation will prove Zs is within the limits, but, oh dear, high resistance joint at least, no earth path at worse.
Lets face it, Specs, if I said it was white, you'd say it was black.
Well I may be wrong Steps but my Fluke meter normally tells me if my neutral is not connected they seem quite clever these Fluke meters.
Hello again jamiep93, I must apologies for some members who seem to like arguing their own opinions on other peoples threads. I assume you have access to a copy of BS7671? Part 2, definitions describes what Zs, Ze, R1, R2 and 'Earth Fault Loop Impedance' are. Guidance note 3 Inspection and testing gives greater detail about determining the earth fault loop impedance. I appreciate that not all students have access to copies of the guidance notes, so for the sake of clarity and to avoid petty arguments, I have added a small extract from guidance note 3 which hopefully may help you and possibly some other members, to understand the relationship between Zs, Ze, R1, R2.
