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.
And thats all the op needs, is a reference point. If you pay for the procerts app, they use the same resistance values in their tables to use as a quick calculation onsite.No don't use that table, it;s ok for reference.
If you had a Ze of 0.75 ohms and an R1+R2 of 1 ohms for a circuit protected by a B16 breaker, would the supply disconnect in under 0.4 seconds under fault conditions?How much would yous let the reading be over before you were to investigate it further as obviously a number of things could effect readings but for like a radial socket in a house on 16amp carrying 6 sockets say the reading was just over 1ohm (just a random figure) would yous want to investigate that further for been high reading
In this case I respectfully disagree, as the OP is not just 1st fixing and dead testing, he is carrying out EICR inspections. A good understanding of electrical theory is very important to determine what is safe and what isn't.And thats all the op needs, is a reference point. If you pay for the procerts app, they use the same resistance values in their tables to use as a quick calculation onsite.
Okay, if i had a radial circuit wired in 6mm/6mm swa and the measured R1/R2 was 0.16ohms. What table or resistance value would you personally use to calculate the length of that circuit as a reference point, and what length would you calculate?In this case I respectfully disagree, as the OP is not just 1st fixing and dead testing, he is carrying out EICR inspections. A good understanding of electrical theory is very important to determine what is safe and what isn't.
I think we have ended up slightly at cross purposes. I have no issue with anyone using OSG, BS7671, Pro Certs, or any other reliable reference of the resistance of copper in order to work out expected R1+R2 values.Okay, if i had a radial circuit wired in 6mm/6mm swa and the measured R1/R2 was 0.16ohms. What table or resistance value would you personally use to calculate the length of that circuit as a reference point, and what length would you calculate?
Since you disagree with using the onsite tables and the procert one, im curious what you would use?
Two things concern me about this thread:
1. The OP is conducting EICRs but not doing any live testing.
2. The OP is conducting EICRs without knowing basic things like how to calculate R1 and R2 values.
3. Sorry there is no third thing
Two things concern me about this thread:
1. The OP is conducting EICRs but not doing any live testing.
2. The OP is conducting EICRs without knowing basic things like how to calculate R1 and R2 values.
3. Sorry there is no third thing
For EICR purposes, the two things that come to mind are how close the calculated Zs is to the limit for the device, and a sense of how big the property you are in is and whether a reading seems plausible. The more you do the easier that gets.All I was wondering is if they was a table about I could use as a guide for r1 r2 readings so I know my readings are correct or slightly high and I need to do abit of further investigation on circuits
Surely a bad connection is going to make BOTH readings off.Previously I’d do dead and live testing and I’d be able to check check the r1 r2 results by the zs readings
Yea I generat know what I’m looking at what seems high and things but I just wanted something to work towards incase I was been slightly generous and over cautious chasing faults that didn’t really need further investigation.For EICR purposes, the two things that come to mind are how close the calculated Zs is to the limit for the device, and a sense of how big the property you are in is and whether a reading seems plausible. The more you do the easier that gets.
e.g. if you're re in 2 up 2 down and you get 1.5 ohms for an immersion heater circuit then a bit of head scratching is due.
The other thing you can do is try RN+R2 or use a wander lead to obtain a 2nd frame of reference, and whether it's R1, R2 or both that have a loose connection.
I'm assuming that you are allowed to do Ze, Zs@DB and RCD tests, and your company only prohibits live Zs readings?
I do know the methods for carrying them and things,This is so basic for someone qualified. Whether dead or live testing, you should know the methods of carrying them out (and working them out) without thinking.
Yea we carry out ze and rcd testsThis is a 'modern' take on Zs testing that you don't do it live except for socket outlets where there is no risk of exposed live parts but as @timhoward asks do you carry out Ze and rcd tests.
Have you ever asked why seems like someone has carried out a risk assessment and deemed it is not safe.Yea we carry out ze and rcd tests
It’s just the zs we don’t carry out
@Lt1990 is only carrying out works in the way as suggested by his company.You are either going to be carrying Zs on lights or sockets principally. Spurs come into it as well. I always do live tests at sockets, spurs and lights. I use the lightmate by Kewtech for Zs test. On courses it has been put to me this is a Lim, as you have to go up a ladder and H&S forbid this in many scenarios. I just get on with the job and test it all. When I put the Zs reading for each circuit I like to be sure I did actually read it with my MFT, I can't imagine any other way to operate. Maybe I am missing something, but I don't think so. Convince me! I mean how do you fill in the forms? Yes calculation, but I am not convinced that is kosher. For instance you can find that there are big variances between R1/R2 + Ze calculation and Zs measured with an MFT.
Where I previously worked we carried out full tests but I’ve only recently started for this place and from what I can gather it’s literally just down to them not wanting us to work live.Have you ever asked why seems like someone has carried out a risk assessment and deemed it is not safe.
I agree with you they is differences from calculations and actually measured results and I use to always do live tests at previous companyYou are either going to be carrying Zs on lights or sockets principally. Spurs come into it as well. I always do live tests at sockets, spurs and lights. I use the lightmate by Kewtech for Zs test. On courses it has been put to me this is a Lim, as you have to go up a ladder and H&S forbid this in many scenarios. I just get on with the job and test it all. When I put the Zs reading for each circuit I like to be sure I did actually read it with my MFT, I can't imagine any other way to operate. Maybe I am missing something, but I don't think so. Convince me! I mean how do you fill in the forms? Yes calculation, but I am not convinced that is kosher. For instance you can find that there are big variances between R1/R2 + Ze calculation and Zs measured with an MFT.
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