Discuss R1 + R2 expected readings in the UK Electrical Forum area at ElectriciansForums.net
Has anyone got a table of expected R1 + R2 readings that give a guide to what readings we should be getting when testin
In most cases that is your starting point. If you just installed a circuit then you should know (at least roughly speaking) how long the run was so multiply that by the table values for the choice of cable and your readings ought to be pretty close to that.Pg 218 of your onsite guide. Length of circuit x resistance ÷ 1000 will give you a rough idea of your R1/R2. Just pace out your run
Baby feet of giant. Or mouse feet in mm.Just pace out your run
well, my long legged strides are roughly a metre, but my apprentice has stumpy legs so i usually halve the number he gives me.Baby feet of giant. Or mouse feet in mm.
The resistance of copper did not change with AM2Does anyone have a photo of table in the on site guide as I’ve misplaced my book so need to get a new and only have the 18th edition blue book at minute
Good advice, as you might have an install fault or it might be as simple as MFT probes not correctly nulled and if you know what to expect, you know when to double-check things.My meter wont work for live testing of R1/R2! Anyway before testing R1 or R1/R2 I always tell any trainess with me to calculate if first so that you know what you should expect before you begin testing. If there is a significant difference you know something is wrong.
It's possible but rather hard work from the blue book (see page 409)and only have the 18th edition blue book at minute
It's early and I'm not caffeinated but that is not making too much sense. The common factor to both tests is the resistance of the cable, with or without faults. Maybe I'm missing you're point.im used to doing both dead and live and been able to see if R1 + R2 is right by the live the testing side of things.
What calculations do you useMy meter wont work for live testing of R1/R2! Anyway before testing R1 or R1/R2 I always tell any trainess with me to calculate if first so that you know what you should expect before you begin testing. If there is a significant difference you know something is wrong. You can easily google resistance table for copper cables. Calculating also applies to RFC tests i.e. r1 r2 and rn as well as R!/R2
So for 2.5mm twin and earth....
Take the 2.5 number (18), divide by 2 as you only want one core's worth of resistance.
Then take the 1.5 number (29) and also divide by 2.
Add that all together. Then divide by 1.2 (temperature correction). That then gives you the number in the OSG
read above.What calculations do you use
i use easy certs and the old version I had at my old company has to highlight high readings in red but this current version doesn’t do itIt's possible but rather hard work from the blue book (see page 409)
Volt drop per meter is given in miliVolt / Amp / metre
Volts = Current X Resistance.
Resistance = Volts / Current.
So that volt drop number is also resistance / meter. But it's for Line and Neutral and you want Line and Earth. It's also not temperature corrects.
So for 2.5mm twin and earth....
Take the 2.5 number (18), divide by 2 as you only want one core's worth of resistance.
Then take the 1.5 number (29) and also divide by 2.
Add that all together. Then divide by 1.2 (temperature correction). That then gives you the number in the OSG
The MUCH easier way is to invest in buying the ProCerts app. Seriously recommended to the degree that I barely use the OSG.
It's early and I'm not caffeinated but that is not making too much sense. The common factor to both tests is the resistance of the cable, with or without faults. Maybe I'm missing you're point.
As your an electrician. Surely you can answer that yourself!View attachment 103371
Could I use this table
Yea but I’m just after double checking things out so I know I’m following the right stuff as still fairly new to it all aswellAs your an electrician. Surely you can answer that yourself!
Use this table to work it outYea but I’m just after double checking things out so I know I’m following the right stuff as still fairly new to it all aswell
Buzz - congratulations my friend! That's the clearest and most coherent post you have ever made on this forum ;-)say we have R1+R2 = 2.35 ( hypothetical figure )
R2 = 1.67 x R1 ( 2.5/1.5mm )
so R1 + ( 1.67xR1 ) = 2.35
( 2.67xR1 ) = 2.35
R1 = 2.35/2.67 = 0.88
R2 = 2.35 - 0.88 = 1.47
( or R2 = 1.67 x 0.88 =1.47)
I am doing eicr tests so it will be just a rough guess to how much cable has been used for calculationsNo don't use that table, it;s ok for reference but you need to use the resistance tables, google them. The whole point being is to work out for yourself the expected measurements as a reference point. When I put in a RFC I know how much cable I have used so say it was 63 m I calculate off of that. Those charts are sort of end user you need to get into the mechanics of how they made those charts.
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