Testing Ring final circuits

[Bonse]

Hi People

So im testing my ring rinal circuit....

i do my end to end test.....

I join incoming CPC to outgoing Line and vice versa......

I then go around my circuit with my tester noting the readings at each socket and record the highest reading.....


Ok so this is my R1+R2 = 0.3

My measured Ze is 0.17Ohms

So my Zs = 0.29 + 0.17

Zs calculated is = 0.46....


Ok so now i reconnect the line and earth in the terminals and liven up my circuit (I have already done the insulation resistance also sorry didnt mention)

Then i goto the socket i got the highest R1+R2 at and do my Zs....


I get a result of 0.31Ohms

Can anyone explain how this is possible?

If Zs= Ze + (R1+R2)

How can i get such different results between calculated and measured?????


Spoke to my friend who has been around a long time and he tells me he does his R1+R2 at the consumer unit.... even though in the OSG it says the way i did it was correct.

When i do it his way i get slightly different readings but they still do not work out in the end....

The circuit is otherwise sound.

Im really looking forward to the replies, oh and yes the leads were nulled


Darren

 

[telectrix]

parallel paths reduce the measured Zs. so your readings seem fine to me.

 

[IQ Electrical]

parallel paths reduce the measured Zs. so your readings seem fine to me.

Exactly, parallel paths at work!

Where was the 0.29 figure from?

 

[domestic spark]

0.29 OP Ze i guessed!

 

[telectrix]

think that was his R1+R2 and on the line above he'd rounded it up. to 0.30

 

[IQ Electrical]

0.29 OP Ze i guessed!

He lists Ze as 0.17

 

[Bonse]

Hi, there were no roundups

and Ze is 0.17 measured at source

 

[Bonse]

Sorry 0.29 is the highest R1+R2

 

[domestic spark]

He lists Ze as 0.17

good point note to self read properly, sorry IQ

 

[Bonse]

no R1+R2 was 0.29

 

[Bonse]

Im with you on this..... if i disconnect the main bonding and retest? theres nothing plugged in within the circuit either

 

[Bonse]

although threres no supplimentry bonding either in this circuit im wondering where the parallel path could be

 

[IQ Electrical]

Im with you on this..... if i disconnect the main bonding and retest? theres nothing plugged in within the circuit either

What are you trying to achieve though, parallel paths are fine!

Even in a simple 'insulated' domestic installation, you have parallel paths everywhere from protective bonding to boiler connections etc. etc.

 

[Bonse]

Im simply testing the equation Zs = Ze + (R1+R2)

and understanding why i can get different measured results to calculated

I do understand the drill just this was niggling me a bit

 

[Jurasic Spark]

Im with you on this..... if i disconnect the main bonding and retest? theres nothing plugged in within the circuit either

Hope you don't mean Zs testing after removing a protective conductor. This should never be done.

Measured Zs is always expected to be lower than Ze + R1 + R2 due to the parallel paths connected to the MET whilst Zs testing.

 

[Bonse]

I said bonding not main protective Conductor

thanks for the input like i said i just wanted to get the result as calculated. as a lot of sparks will calculate and be happy with the result

 

[Bonse]

Loving the fast responses on this forum! not used to this cheers

 

[Bonse]

basically the answer is parallel paths....

The fact that the Zs is lower than Ze + (R1+R2) is fine on the test certificate.

Thanks everyone much appreciated!

 

[IQ Electrical]

basically the answer is parallel paths....

The fact that the Zs is lower than Ze + (R1+R2) is fine on the test certificate.

Thanks everyone much appreciated!

That's about it, a competent person reading the test results would expect that scenario.

 

[Bonse]

Cheers IQ!

 

[Bonse]

Cheers everyone in fact!

 

[Jurasic Spark]

That's about it, a competent person reading the test results would expect that scenario.

Correct, and in actual fact if the Measured Zs recorded on the SOTR was equal to the recorded Ze plus the recorded R1 + R2 then a competent person checking your results would be very suspicious of your R1 + R2 readings. He would probably suspect that they weren't resistance readings at all. ;0)

 

[IQ Electrical]

Correct, and in actual fact if the Measured Zs recorded on the SOTR was equal to the recorded Ze plus the recorded R1 + R2 then a competent person checking your results would be very suspicious of your R1 + R2 readings. He would probably suspect that they weren't resistance readings at all. ;0)

Lol, but do remember that in accordance with Guidance Note 3, calculation of Zs from Ze+(R1+R2) is acceptable

 

[Bonse]

So to eliminate parallel paths a calculations probably better, or do both and if he measured result is less than the calculated it can be down to parallel paths whith is acceptable

All good stuff guys!

Be reading GN3 again!

 

[Jurasic Spark]

Lol, but do remember that in accordance with Guidance Note 3, calculation of Zs from Ze+(R1+R2) is acceptable

Correct again, but I still reckon he would suspect you did it the other way round ;o)

 

[Bonse]

Sorry iphone type!

 

[Bonse]

I would happily show such person the sequence of tests to prove these are hactual results