circuit resistance

[scott.rick]

could someone give me some help calculating a circuit resistance for a single phase circuit as it would be entered on a minor works cert if tested?

the circuit in question is a supply from a 2.5mm T&E 30m long going to fused spur then into 1.5 T&E 15m Long.

1st is the calculation done as two seperate calcs one for each cable size or just for the smaller cable?

also if i have a Ze of 0.8 how would i do the working out for the correct r1 + r2 for this circuit?

i think i have one over too much information and confused myself!!!!!

 

[monkeyelectric]

could someone give me some help calculating a circuit resistance for a single phase circuit as it would be entered on a minor works cert if tested?

the circuit in question is a supply from a 2.5mm T&E 30m long going to fused spur then into 1.5 T&E 15m Long.

1st is the calculation done as two seperate calcs one for each cable size or just for the smaller cable?

also if i have a Ze of 0.8 how would i do the working out for the correct r1 + r2 for this circuit?

i think i have one over too much information and confused myself!!!!!

Are you talking about insulation resistance or r1 + r2? r1 + r2 should be taken from direct measurement or do a zs test and subtract ze to get r1 + r2

 

[scott.rick]

Are you talking about insulation resistance or r1 + r2? r1 + r2 should be taken from direct measurement or do a zs test and subtract ze to get r1 + r2

so if i have a measurement of Zs 0.6 on my tester and a Ze of 0.8 how would i get the r1 = r2?

 

[monkeyelectric]

so if i have a measurement of Zs 0.6 on my tester and a Ze of 0.8 how would i get the r1 = r2?

Is it a tns? can you take a direct measurement of r1 + r2?

zs = ze + r1 +r2

 

[scott.rick]

Is it a tns? can you take a direct measurement of r1 + r2?

zs = ze + r1 +r2

the measurement on my megger for r1 + r2 is coming up as 0.22 and the Zs reading is 0.6 can this be right or am i missing something here?

the measurement on my megger for r1 + r2 is coming up as 0.22 and the Zs reading is 0.6 can this be right or am i missing something here?

 

[monkeyelectric]

the measurement on my megger for r1 + r2 is coming up as 0.22 and the Zs reading is 0.6 can this be right or am i missing something here?

Sounds like parallel paths try disconnecting your bonding and doing zs again
Your ze is definately 0.8? is it a tns system?

 

[scott.rick]

is this measurement wrong then? what should the R1 + R2 compared to Zs 0.6 or vice versa Be!! im def confused now if i disconnect bonding and put that on a minor works certificate wont this not be incorrect readings for circuit being tested once bonding reconnected and put into service

 

[monkeyelectric]

is this measurement wrong then? what should the R1 + R2 compared to Zs 0.6 or vice versa Be!! im def confused now if i disconnect bonding and put that on a minor works certificate wont this not be incorrect readings for circuit being tested once bonding reconnected and put into service

Like i said before it should be zs = ze + r1 + r2, sorry bud if you don't know how to work these out you should'nt be doing the work anyway

 

[old dog]

2.5 t&e 30meters long 7.41+12.10x30/1000 =0.58

1.5 t&e 15meters long 12.10+18.10x15=0.45

(R1+R2)=1.03

 

[Risteard]

Are you talking about insulation resistance or r1 + r2? r1 + r2 should be taken from direct measurement or do a zs test and subtract ze to get r1 + r2

Whilst Zs can be measured or calculated I don't believe you are allowed to subtract your Ze from Zs to give you (R1+R2). Don't forget parallel paths would be included.

Someone also mentioned disconnecting bonding. This should never be done on a live installation - as such you cannot measure Zs with an EFLI tester with the bonding disconnected.

 

[old dog]

zs=ze+(R1+R2) you can use this to calculate for zs but not for (R1+R2)

 

[monkeyelectric]

zs=ze+(R1+R2) you can use this to calculate for zs but not for (R1+R2)

Sorry guys my mistake, i personally always measure everything anyway so never do the calculations to work the stuff out i just know the relationship between them all, its been a long week and my head is fried