Testing with a CU change

[Bradley6969]

Working with a spark, now when we change a CU no new circuits just old for new, We do all end to ends on rings, IR tests and Zs making sure all the new protective devices that disconnection times are met, would you do R1+R2?

If we do a CU change and add new circuits we do R1+R2 on the new circuits what do you guys do?

 

[Ian1981]

Agree But you also don't calculate R1+R2 and design stage either , you calculate Zs from by inquiring what the Ze will be and adding that your R1+ R2 readings, As others have said you can't back calculate the R1+R2 but I believe loads sparks who do it, As for the ops question, I do all the test except Zs which I calculate .

Of course you can calculate your R1+R2 at design.
It’s not what I would record on the EIC as I would measure it during initial verification however when deciding what cables to use then using the mv/a/m values at 20 degrees and multiplying by 1.2 will give me a ball park figure of design, added to the Ze I can see what my Zs should be for compliance with disconnection times

 

[TJ Anderson]

Agree, we can and do just that. I'm sure you meant the OSG Table L1 (R1+R2)/Metre Values as opposed to mV/A/m for the calculated value though

 

[Ian1981]

Agree, we can and do just that. I'm sure you meant the OSG Table L1 (R1+R2)/Metre Values as opposed to mV/A/m for the calculated value though

Yep not the volt drop mv/A/m oops

 

[Richard Burns]

Though Volts/ amps does give resistance so they are valid figures for resistance!!

 

[magnoliafan89]

I always do zs but dont bother filling in R1+R2 unless i actually test it. I never see the point people calculating R1+R2 or even zs on a test form if you dont test dont bother.
I know lots of people do but meh.

Was taught the calculation at college and nowadays at the am2 you have to calculate the R1+R2 before actually then testing by using the formula R1 reading + the R2 reading and dividing by 4.

 

[TJ Anderson]

Though Volts/ amps does give resistance so they are valid figures for resistance!!

Yeah, definitely. I typo'd too, meant table I1.

If you take any of the mV/A/m values and ÷ 2.4 it will give you the values of (R1 + R2) / Metre in Table I1.

 

[Richard Burns]

Yeah, definitely. I typo'd too, meant table I1.

If you take any of the mV/A/m values and ÷ 2.4 it will give you the values of (R1 + R2) / Metre in Table I1.

I had never actually thought of it like that but that is much simpler!
I looked at that and thought what is he talking about then actually thought and went, oh yeah!
I was thinking volt drop is over the length of circuit for both line and neutral and at 70°C, so twice the length so I can take the R1+R2 values for same size cpc and line in table I1, or divide by 2, however I need to correct from 70°C to 20°C so also divide by 1.2.
However using the single conductor value in I1 and multiplying by twice 1.2 (2.4) or vice versa is a lot more straightforward.