Calculating R2 from R1 and RN

[Superspark23]

WHen doing the continuity of a ring main and the cpc is 1.0mm should the reading be 1.25 times the R1 or Rn value. And 1.75 if its 1.5mm?

 

[SMB]

its 1.67 times for 1.5mm cpc.

Not sure for 1mm cpc im afraid.

 

[i=p/u]

i would say little more for 1mm

 

[telectrix]

i would say little more for 1mm

right. look at the ratios. 2.5:1. that would give a value for R2 at 2.5 x R1. SSSSiimmmmppplleeessss

 

[tony mc]

2.5/1.0 = 2.5 6.0 /2.5 = 2.4 etc

Just dived the line conductor by the cpc to get you ratios

 

[Sparky Ninja]

R2 = (RTXA1)/(A1+A2)

or

R1 = (RTXA2)/(A1+A2)

Where A= The CSA of the conductor.

 

[Superspark23]

R2 = (RTXA1)/(A1+A2)

Where A= The CSA of the conductor.

Whats RT refering to? and is A1 say the size of cpc csa? and A2 the csa of the line conductor?

 

[Sparky Ninja]

Whats RT refering to? and is A1 say the size of cpc csa? and A2 the csa of the line conductor?

RT represents the total, in this case, the R1&R2.

A1 is the CSA of R1, and A2 is the CSA of R2.

For example... say you have an R1&R2 of 0.85ohms and you want to determine R1, Rn and R2. In theory we can determine Rn from obtaining R1's value.

So..

R1&R2 = 0.85 ohms..

R2 = (RTXA1)/(A1+A2) = (0.85x2.5)/(2.5+1.5) = 0.53 ohms

R1 = (RTXA2)/(A1+A2) = (0.85x1.5)/(2.5+1.5) = 0.32 ohms

So we have (R1) 0.32 ohms + (R2) 0.53 ohms = 0.85 ohms (R1&R2)

 

[Superspark23]

RT represents the total, in this case, the R1&R2.

A1 is the CSA of R1, and A2 is the CSA of R2.

For example... say you have an R1&R2 of 0.85ohms and you want to determine R1, Rn and R2. In theory we can determine Rn from obtaining R1's value.

So..

R1&R2 = 0.85 ohms..

R2 = (RTXA1)/(A1+A2) = (0.85x2.5)/(2.5+1.5) = 0.53 ohms

R1 = (RTXA2)/(A1+A2) = (0.85x1.5)/(2.5+1.5) = 0.32 ohms

So we have (R1) 0.32 ohms + (R2) 0.53 ohms = 0.85 ohms (R1&R2)

Thanks so using your formulars. I have worked out that when checking the continuity of ring mains i need to times my r1 value by either 1.67 for 1.5mm cpc or 2.5 for 1.0mm cpc

so an r1 reading of 0.20 with 1.5mm cpc should provide me with an reading of 0.33 i'll see how these work on site tomorrow.

 

[i=p/u]

what about rn

 

[Superspark23]

Rn will allways be the same as R1 because they are the same CSA if you have a difference of more than 0.02 ohms you have to investigate this. That is providing the Neutral is the same legnth as the Line conductor, which in a ring it will be.

 

[i=p/u]

easy info thanks, think im over doing it

 

[IQ Electrical]

Rn will allways be the same as R1 because they are the same CSA if you have a difference of more than 0.02 ohms you have to investigate this. That is providing the Neutral is the same legnth as the Line conductor, which in a ring it will be.

0.05 Ohms is the accepted difference.

 

[rocker]

Just divide the big one by the small one. The difference in CSA is directly proportional to the difference in resistance.

 

[telectrix]

what about rn

should be same as r1