R2 Testing

[sparky1ste]

Hi All,Testing high level lights in a factory,on this occasion i did R2 test as i couldnt reach the lights.when recording values how do i record zs values when caculating.

 

[Farmelectrics]

Find out the conductor size of the lighting circuit and then you will be able to calculate your zs by using the formula zs=ze[r1+r2] ie if the conductors are the same size then r1will be the same as are r2 if not and eart is smaller the1.7 value comes in refer to gn3

 

[GaryM]

Nice low earth path if metal fittings are bolted to bonded structural steel...
Zs would go down as a limitation for me if I couldn't access to test.

 

[sparky1ste]

so in this instance i have to work backwards and caculate my R1 (1.5T+E) then do the norm

 

[sparky1ste]

i would off normally put it down a lim however the person verifiying my report says different

 

[JUD]

...if not and eart is smaller the1.7 value comes in refer to gn3

That would be 1.67 and that's only for 2.5/1.5mm² i.e 2.5 ÷ 1.5 = 1.67.

However the OP needs to do things the other way round, if indeed the cpc is smaller than the line. If this is the case take the R2 reading and multiply it by (cpc size ÷ line size). The result will be R1. Add this back to R2 to get R1+R2..

R1+R2 = (R2 x (cpc ÷ line)) + R2
Zs = Ze + ((R1+R2) x 1.2)

 

[GaryM]

I don't see how you can calculate an R1 or a Zs from an R2 reading that may have parallel earth paths and an R1 which may have poor connections.
limitation is the only way if you can't access for testing.

 

[Farmelectrics]

Yes your right jud 1.67 should check before posting missed 6 off you would get good r2 readings as Gary said due to parllel earths

 

[Farmelectrics]

Yes ok jud your right and in hindsight putting no access to do zs readings on high bay lights maybe the answer long day and a heavy weekend lol

 

[Farmelectrics]

Jud just a last one before I retire for the night were did you get r2 divided by the CPc formula from if I'm honest not come across it before not seen it in any books please advise

 

[JUD]

I don't see how you can calculate an R1 or a Zs from an R2 reading that may have parallel earth paths and an R1 which may have poor connections.
limitation is the only way if you can't access for testing.

Agreed. My post was really in response to farm's post about the 1.67 value and how the value of R1 could be calculated from the value of R2 assuming you had no parallel paths etc.

 

[GaryM]

It's just maths and not an electrical formula as such.

 

[JUD]

Jud just a last one before I retire for the night were did you get r2 divided by the CPc formula from if I'm honest not come across it before not seen it in any books please advise

The 1.67 value comes from the same formula and is for 2.5mm² with a 1.5mm² cpc...

R2 = R1 x (2.5 ÷ 1.5)
R2 = R1 x 1.67

If you had the value of R2 then the part inside the brackets gets reversed...

R1 = R2 x (1.5 ÷ 2.5)
R1 = R2 x 0.6

As another example the formulas for 6mm² with a 2.5mm² cpc would be...

R2 = R1 x (6 ÷ 2.5)
R2 = R1 x 2.4

R1 = R2 x (2.5 ÷ 6)
R1 = R2 x ​0.42

It's just ratios

Small error. It's multiply not divide. Corrected above