R1 + R2 expected readings

[Vortigern]

No 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.

 

[buzzlightyear]

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)

 

[timhoward]

I've already explained (or tried to) how to work this out for yourself. If you don't understand, then feel free ask more questions.

Again, I'd highly recommend getting an app.
The one (and several other people on here) use has simple tables that are accurate, and also the max Zs values, among many other helpful things.
One off payment of £18.

Electrical Tools & Reference - Apps on Google Play

THE Electricians App , electrical calculators, charts, tables, tools & guides.

play.google.com

‎Electrical Tools and Reference

‎The Electrical App for Electricians, Electrical Engineers and anyone working within the Electrical Industry. This Electrical Tools and Reference App is packed full of printable electrical charts & tables, multiple electrical calculators and electrical technical guides. APP MAIN SECTIONS: -...

apps.apple.com

 

[timhoward]

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)

Buzz - congratulations my friend! That's the clearest and most coherent post you have ever made on this forum ;-)

 

[Lt1990]

No 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.

I am doing eicr tests so it will be just a rough guess to how much cable has been used for calculations

 

[Lt1990]

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

 

[ethernet]

No don't use that table, it;s ok for reference.

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.

 

[timhoward]

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

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?

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.

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.

 

[Vortigern]

What are you measuring and getting the figure 1 ohm From the circuit you descibe I would expect something around .3-.6 ohm max. I would expect age and installation technique would vary that figure if it was 1 ohm fine (ish) but would get my spider sense running looking for poor termination at sockets for instance. The critical figure at each socket would be the Zs and its compliance for ADS and if the 1ohm figure was still there for say R1 it is unlikely I would work through all the sockets to re-terminate not enough money or time for that.

 

[ethernet]

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.

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?

Im assuming the op is an approved electrician if he's doing eicrs, so should have a sound knowledge of electrical theory

 

[timhoward]

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?

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.

My emphasis was intended to be on the "all the OP needs".
I'm a little bit concerned that anyone is having to undertake EICRs and asking some of the questions above, apparently without being provided with the latest regs book or OSG.
I don't mind using this forum to further my own understanding and in turn to try and help other people increase their understanding, but sometimes it feels like people are put in impossible situations by their employers and are expected to run before they can walk.

 

[loz2754]

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

 

[DPG]

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

The third thing for me is that the OP doesn't seem to see the problem of the first two points.

 

[buzzlightyear]

The op can grasp the concept on testing
R1+R2 and calculations on how to do it
My advice is to get a good book on testing.

 

[Lt1990]

I have a good understanding on electrics and testing and what I should be looking for and testing
The company I now work for only require us to do dead testing and then calculate the zs readings
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
Previously I’d do dead and live testing and I’d be able to check check the r1 r2 results by the zs readings

 

[Lt1990]

If I had my own way I’d be doing dead and live testing but when the company doesn’t want us doing it and to just calculate zs results then I’m going to do what I’ve been told to

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

 

[DPG]

Does nobody do any live testing?
Who signs the certs?

 

[timhoward]

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

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?

 

[ipf]

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.

 

[westward10]

This 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.