Confused! R1+R2 from Zs-Ze commercial EICR

[Electreacle]

Hi all, just started a new job and I was shadowing another electrician. This was within a commercial setting as only 20% testing was carried out due to it being tested every year a full 100% would of been conducted at the end of the 5 years.

I was always taught to measure R1+ R2 and measure Ze then do the required formula to get Zs (Zs = Ze + R1 + R2) .

The spark picked 4 circuits and did not once do an R1 + R2. He just calculated it from his measured Ze and Zs of each tested circuit.

He said this is what others do. I know people do things differently from text book to real world but is this common within the commercial sector to do so?
I don’t feel like this is correct as I’ve never once been shown this way of testing. Would this be ok if I had access to previous test results and the value of the Ze and Zs values were similar on the old certs?

I’m still shadowing this spark but they are putting me out on my own in 2 weeks and I don’t want to be learning bad habits.He made out like this is common practice in the commercial testing sector. Confused. I do know how to test it’s just this one method that is confusing me. Should I carry on measuring the R1 + R2 or is calculation ok?

Appreciate your response's in advance

 

[westward10]

On an initial verification you would do R1+R2 as one of the dead tests as you are verifying the integrity of the circuit before it is made live. For an EICR this isn't generally necessary (see Table 3.4 and it's Notes in GN3).
This is all further complicated by the way in which colleges now demonstrate testing for the C&G 2391 whereby live Zs testing is restricted to socket outlets and other circuits are done by the formula you suggest. You are working with older electricians who think nothing of working live for Zs which is now frowned upon but it is quicker and the world of EICRs likes quicker. You must do whatever you feel most comfortable with and your companies policy for live testing.

 

[DefyG]

working live for Zs which is now frowned upon

My meter doesn't record a loop test (Zs) unless the circuit is 'Live'?

 

[westward10]

My meter doesn't record a loop test (Zs) unless the circuit is 'Live'?

What I meant was working live for a Zs whilst using the flyleads, yes it obviously has to be live. The way it is taught now is to avoid this and calculate it although it seems acceptable to do Ze and PFC in this manner.

 

[DefyG]

Sorry, yes I realised there was more to what you meant.
I was taught to do dead tests for theoretical Zs and live tests to compare with design calcs - but time consuming!!

 

[Pretty Mouth]

Hi all, just started a new job and I was shadowing another electrician. This was within a commercial setting as only 20% testing was carried out due to it being tested every year a full 100% would of been conducted at the end of the 5 years.

I was always taught to measure R1+ R2 and measure Ze then do the required formula to get Zs (Zs = Ze + R1 + R2) .

The spark picked 4 circuits and did not once do an R1 + R2. He just calculated it from his measured Ze and Zs of each tested circuit.

He said this is what others do. I know people do things differently from text book to real world but is this common within the commercial sector to do so?
I don’t feel like this is correct as I’ve never once been shown this way of testing. Would this be ok if I had access to previous test results and the value of the Ze and Zs values were similar on the old certs?

I’m still shadowing this spark but they are putting me out on my own in 2 weeks and I don’t want to be learning bad habits.He made out like this is common practice in the commercial testing sector. Confused. I do know how to test it’s just this one method that is confusing me. Should I carry on measuring the R1 + R2 or is calculation ok?

Appreciate your response's in advance

The way you were taught to calculate Zs for a circuit is correct, it will give an accurate value for proving that the protective device will operate. The actual measured Zs may be lower than calculated, due to parallel paths to earth, but it won't be higher.

The way your spark friend calculated R1+R2 from measured Zs and Ze, however, is incorrect, for the same reason. It's likely to give an artificially low result due to parallel paths.

Example: A circuit powering a boiler has a disconnected CPC, so true R1+R2 is infinity. However, Zs measured at the FCU to the boiler may give a perfectly acceptable result, due to the parallel path made through the copper pipework and main bonding. Calculating the R1+R2 from the Zs and Ze, in this case, would give a totally inaccurate value.

That said, as Westward notes, it's not always necessary to provide an R1+R2 for the circuit, nor is it always necessary to provide a Zs.

 

[Electreacle]

On an initial verification you would do R1+R2 as one of the dead tests as you are verifying the integrity of the circuit before it is made live. For an EICR this isn't generally necessary (see Table 3.4 and it's Notes in GN3).
This is all further complicated by the way in which colleges now demonstrate testing for the C&G 2391 whereby live Zs testing is restricted to socket outlets and other circuits are done by the formula you suggest. You are working with older electricians who think nothing of working live for Zs which is now frowned upon but it is quicker and the world of EICRs likes quicker. You must do whatever you feel most comfortable with and your companies policy for live testing.

Thank you for your knowledgeable response
Yes looking at Pages 128 & 129 of GN3 leans towards the comment of if changes were made to the circuit then

 

[Electreacle]

Thank you both for your knowledgeable replies.. As you mentioned in GN3 it’s only viable to carry out the R1 + R2 on an EICR if you suspect the circuit has been altered in any way.. I think I will be performing an R1 + R2 on the circuits that I can get access to.. rather than putting a lim on the circuit in that respect would you suggest recording the R1+ R2 from the formula of Zs- Ze? And corroborating these values and the Ze and Zs and see if it is similar In Resistance values?

 

[Pretty Mouth]

Thank you both for your knowledgeable replies.. As you mentioned in GN3 it’s only viable to carry out the R1 + R2 on an EICR if you suspect the circuit has been altered in any way.. I think I will be performing an R1 + R2 on the circuits that I can get access to.. rather than putting a lim on the circuit in that respect would you suggest recording the R1+ R2 from the formula of Zs- Ze? And corroborating these values and the Ze and Zs and see if it is similar In Resistance values?

I'm not sure I fully understand your question, so hopefully my answer is relevant, let me know if not.

I would not record an R1+R2 value on the test results sheet unless I had actually measured it with a continuity test.

 

[Electreacle]

I'm not sure I fully understand your question, so hopefully my answer is relevant, let me know if not.

I would not record an R1+R2 value on the test results sheet unless I had actually measured it with a continuity test.

Sorry for the confusion. But you answer is relevant. So it sounds like you’d be leaning more towards measuring it rather than transposing the calculation. I just want to do it right.. your points are valid at the same time GN3 doesn’t require us to measure it. No wonder these sparks are smashing EICRs out

 

[Pretty Mouth]

Sorry for the confusion. But you answer is relevant. So it sounds like you’d be leaning more towards measuring it rather than transposing the calculation. I just want to do it right.. your points are valid at the same time GN3 doesn’t require us to measure it. No wonder these sparks are smashing EICRs out

Typically (depending on what type of circuit it is) I would measure R1+R2, and calculate the circuit Zs from that. If I'd just measured Zs for the circuit, then I'd leave the R1+R2 cell blank (I think you're actually supposed to put N/V there, but I leave it blank).

My work's almost always domestic, so I may have a different approach to EICRs to you. Usually I have no previous test results, and there can be decades of dodgy alterations there, co it can sort of be a hybrid of initial verification and fault-finding. Whereas it sounds like your installations are tested and recorded regularly, so I think you can approach it differently. What sort of circuits are they that you're testing?

 

[Electreacle]

Typically (depending on what type of circuit it is) I would measure R1+R2, and calculate the circuit Zs from that. If I'd just measured Zs for the circuit, then I'd leave the R1+R2 cell blank (I think you're actually supposed to put N/V there, but I leave it blank).

My work's almost always domestic, so I may have a different approach to EICRs to you. Usually I have no previous test results, and there can be decades of dodgy alterations there, co it can sort of be a hybrid of initial verification and fault-finding. Whereas it sounds like your installations are tested and recorded regularly, so I think you can approach it differently. What sort of circuits are they that you're testing?

It seems to mainly be restaurant chains and pubs

Typically (depending on what type of circuit it is) I would measure R1+R2, and calculate the circuit Zs from that. If I'd just measured Zs for the circuit, then I'd leave the R1+R2 cell blank (I think you're actually supposed to put N/V there, but I leave it blank).

My work's almost always domestic, so I may have a different approach to EICRs to you. Usually I have no previous test results, and there can be decades of dodgy alterations there, co it can sort of be a hybrid of initial verification and fault-finding. Whereas it sounds like your installations are tested and recorded regularly, so I think you can approach it differently. What sort of circuits are they that you're testing?

It mainly seems to be restaurant chains and pubs. I think I will be measuring R1 + R2 and calculating Zs unless it’s a socket circuit I will measure it.

 

[Pretty Mouth]

It seems to mainly be restaurant chains and pubs


It mainly seems to be restaurant chains and pubs. I think I will be measuring R1 + R2 and calculating Zs unless it’s a socket circuit I will measure it.

Just something to be mindful of: an R1+R2 test on its own won't prove polarity, it won't show a L-E reversal. It would be unusual to find this sort of fault in an installation that has been in service for some time, but could happen where accessories have been swapped, especially sockets. I typically also do an R1+RN test, or an RN+R2, which along with the R1+R2 will prove correct polarity. RN+R2 is useful, as it can often be directly compared to R1+R2 without calculation.