zs unexpected results

[scott 123]

Testing a ring final ..ze = 0.22
.r1 + r2 =0.65...
R2 +rn = 0.69
So calculated zs = 0.87
But when I test at sockets they are around 1.47

 

[SJD]

Testing a ring final ..ze = 0.22
.r1 + r2 =0.65...
R2 +rn = 0.69
So calculated zs = 0.87
But when I test at sockets they are around 1.47

By mixing use of upper & lower case "r" in your post, it is difficult to be sure what you mean.

 

[Pete999]

Testing a ring final ..ze = 0.22
.r1 + r2 =0.65...
R2 +rn = 0.69
So calculated zs = 0.87
But when I test at sockets they are around 1.47

Don't know what happened to my last post so here goes again, your r1+r2 result, is that the figure of eight result? ( R1+R2)
Losing it big time here the result of 1.47 ohms is that the average of all the sockets? or is it from one particular socket which could be a spur?

 

[telectrix]

your R1+R2 should be (r1+r2)/4 i.e. approx 0.17. add that to 0.22 and you get Zs= 0.39.

 

[scott 123]

Don't know what happened to my last post so here goes again, your r1+r2 result, is that the figure of eight result? ( R1+R2)
Losing it big time here the result of 1.47 ohms is that the average of all the sockets? or is it from one particular socket which could be a spur?

Yes to the figure of eight and yes it was the average sockets were reading between 1.43 and 1.5

 

[Buckfast]

Is the ring a new installation or old. Contacts on older ring socket outlets can fur up badly if not used which could lead to high readings. Take a couple of readings from back of socket and compare.

 

[HappyHippyDad]

That is a little hard to understand Scott as, like the others have said, you've mixed up lower and upper case.

I find if anything when measured at sockets it can be 'less' then Ze + (R1+R2) due to Main bonding. Have you measured with a plug in tester? If so, it may be a good idea to use someones elses tester to see if you get the same results, or perhaps take the socket off and test actually on the conductors.

 

[Deleted member 72666]

As above, take readings from the terminals and not from the front of the sockets.

 

[HappyHippyDad]

Yes to the figure of eight and yes it was the average sockets were reading between 1.43 and 1.5

In that case scott, your Zs was 1.5 I'm afraid :sick:. It's just gone up by another 0.03!

 

[Engineer54]

Testing Zs via a plug top lead can always give you false values even on new installs and why i rarely if ever use them. Test at the sockets terminals if you want accurate values that aren't relying on what is, just a scraping plug top connection..

 

[Octopus]

I'm a bit suspicious of ALL the readings being the same. Are you sure you nuled the leads and had the tester on the correct setting?

 

[Deleted member 9648]

Are you testing on the no trip setting on your meter? In practice this rarely gives accurate results....usually higher than the actual value. I had this discussion with Megger after I found that my meter gave wildly variable results on successive tests on the same point.Their reply was that accuracy isnt that important on the no trip setting as the RCD means much higher values are acceptable anyway!!. Renders the no trip setting a little pointless IMO.

 

[tony mc]

Agree with Wirepuller re the no trip!

Also when using the No Trip 15mA setting you can with certain RCD's get unusually high ZS readings due to the internals of the device.

Alarmbells should start ringing if the results are not what you expect and a futher bit of investigation work is needed to see if there is a problem!

Bypass the RCD and ZS the circuit from the DB using the 25A high current ZS test if in doubt!

 

[sparksburnout]

Like tony mc has said, bypass the RCD, it's probably messing the reading up.

 

[PEG]

Agree with Wirepuller re the no trip!

Also when using the No Trip 15mA setting you can with certain RCD's get unusually high ZS readings due to the internals of the device.

Alarmbells should start ringing if the results are not what you expect and a futher bit of investigation work is needed to see if there is a problem!

Bypass the RCD and ZS the circuit from the DB using the 25A high current ZS test if in doubt!

This is going to start one of those debates....

It is exactly,what a competent tester could consider,as part of his investigation,but is frowned upon,by some assessors and instructors.

I reckon it is part of simplifying the instruction process,or one of a number of other reasons.

I have had this from trainers,and read this in many testing instructional books,but cannot see the difference between this "bypassing" and other bypass procedures,such as disconnecting bonding,for the purpose of a specific test.

One assessor i spoke to,concerning this anomaly,told me eventually "...well,bonding is one conductor,and one terminal..." and that bypassing any RCD,was "more involved..."

...Maybe it's just the same feeling of frustration,older dudes have,on finding some grads dissertation got a 1:1,with a spelling mistake on every other line,"coz,the content trumped it..." :icon12: