R1 + R2 expected readings

[Lt1990]

Has anyone got a table of expected R1 + R2 readings that give a guide to what readings we should be getting when testing

 

[Lt1990]

It'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.

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 it
And in regards to testing I am only doing dead tests basically so would have liked a table to just check results

 

[Lt1990]

Could I use this table

 

[ethernet]

View attachment 103371
Could I use this table

As your an electrician. Surely you can answer that yourself!

 

[Lt1990]

As your an electrician. Surely you can answer that yourself!

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 aswell

 

[ethernet]

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 aswell

Use this table to work it out

 

[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.

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‎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