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.