Periodic - few things

[Monkey1984]

Been along time since I've had the need to do a periodic inspection so thought I would go out and view one being done by a colleague. So a few things I'd like some views on.

Ze=0.41 Ohms.

1. R1+R2 reads on certain circuits are coming in above Eli? For example socket circuit (32A Ring) R1+R2: 1.06 Ohms, but Eli from same socket is 0.96 Ohms? There is some interconnections on the circuit as the readings are not consistant on Ring integrity test. Any ideas?

2. Interconnections on ring. What code would you use? Colleague downgraded circuit from 32A to 20A for safety until resolved. He is thinking code 1. I was thinking 2 bcause of the change of fuse protecting circuit.

3. Earthing arrangement is TN-C-S but Ze is 0.41. Code 1? I know it's only slighty over but due to the type of form this is then it needs to be put on observations.

4. Socket under sink seems to at some point have had some water ingress as there is now a piece of plastic covering the socket? This is feeding washing machine / dishwasher but surely this has to be a code 1?

There will be more but this is all I can remember going to have a chat with him tomorrow to discuss. Any thoughts questions?

 

[trebor]

Been along time since I've had the need to do a periodic inspection so thought I would go out and view one being done by a colleague. So a few things I'd like some views on.

Ze=0.41 Ohms.

1. R1+R2 reads on certain circuits are coming in above Eli? For example socket circuit (32A Ring) R1+R2: 1.06 Ohms, but Eli from same socket is 0.96 Ohms? There is some interconnections on the circuit as the readings are not consistant on Ring integrity test. Any ideas?

2. Interconnections on ring. What code would you use? Colleague downgraded circuit from 32A to 20A for safety until resolved. He is thinking code 1. I was thinking 2 bcause of the change of fuse protecting circuit.

3. Earthing arrangement is TN-C-S but Ze is 0.41. Code 1? I know it's only slighty over but due to the type of form this is then it needs to be put on observations.

4. Socket under sink seems to at some point have had some water ingress as there is now a piece of plastic covering the socket? This is feeding washing machine / dishwasher but surely this has to be a code 1?

There will be more but this is all I can remember going to have a chat with him tomorrow to discuss. Any thoughts questions?

1. its quite common for the ELI to be lower than the Ze +R!+ R2 due to parallel earth paths

2. interconnections on an rfc require further investigation

3. 0.41 is high for TN-C-S, try line to neutral as it should be the same on pme, if its lower maybe do the Ze test again , 0.35 is the max quoted for pme, normally around 0.18

4 any water ingress must be a code 1 especially under a sink

 

[pevvers]

Been along time since I've had the need to do a periodic inspection so thought I would go out and view one being done by a colleague. So a few things I'd like some views on.

Ze=0.41 Ohms.

1. R1+R2 reads on certain circuits are coming in above Eli? For example socket circuit (32A Ring) R1+R2: 1.06 Ohms, but Eli from same socket is 0.96 Ohms? There is some interconnections on the circuit as the readings are not consistant on Ring integrity test. Any ideas?

Parallel earth paths will bring down the Zs readings. Was this the figure of 8 test you were using for R1+R2 or calculation from end to end test?

2. Interconnections on ring. What code would you use? Colleague downgraded circuit from 32A to 20A for safety until resolved. He is thinking code 1. I was thinking 2 bcause of the change of fuse protecting circuit.

Code 2 for this fault.

3. Earthing arrangement is TN-C-S but Ze is 0.41. Code 1? I know it's only slighty over but due to the type of form this is then it needs to be put on observations.

Speak to the DNO. As far as I am aware they are happy for slightly high readings on TN-C-S supplies.

4. Socket under sink seems to at some point have had some water ingress as there is now a piece of plastic covering the socket? This is feeding washing machine / dishwasher but surely this has to be a code 1?

I would say a code 2, as it's not an immediate danger which would be find be bare live conductors etc.

Try having a look at the ESCs Best Practice Guide 4 found here: -

Best Practice Guides | Electrical Safety Council

They will be able to give you codes that all the big players in the industry agree with and is good guide for people not sure about coding, and something in black and white for you to use in the event of someone disagreeing with them!

------------------

Someone beat me to it, the joys of PIR coding, everyone has a different opinion!

I wouldn't say that water ingress is an immediate danger, and all code 1's should be followed up immediately and rectified if possible....

 

[Monkey1984]

Parallel earth paths will bring down the Zs readings. Was this the figure of 8 test you were using for R1+R2 or calculation from end to end test?

Speak to the DNO. As far as I am aware they are happy for slightly high readings on TN-C-S supplies.

1. Figure of 8 used to test ring integrity. Although it highlighted interconnections. I know for a fact this was tested ok as I double checked this due to the vast difference in readings.

2. The client will contact EDF and advise them on the difference I mean it's not vastly over. Thing is because it has shown up when peforming the Pir would a code 3 be advisable as it requires further investigation from DNO.

1. its quite common for the ELI to be lower than the Ze +R!+ R2 due to parallel earth paths

2. interconnections on an rfc require further investigation

3. 0.41 is high for TN-C-S, try line to neutral as it should be the same on pme, if its lower maybe do the Ze test again , 0.35 is the max quoted for pme, normally around 0.18

4 any water ingress must be a code 1 especially under a sink

in reference to point 3 - line / neutral tested and came out 0.55 Ohms so was in fact higher.

 

[joe_berks]

i might sound a bit stupid, but what is ELi?

 

[Guest123]

Earth Loop Impedance.

EFLI in my book.

 

[Monkey1984]

Earth Loop Impedance.

EFLI in my book.

You are of course correct. ;-).

Got a copy of the results this morning.

Some Efli ;-) are higher then R1+R2 and some are lower does that seem correct? Another Couple of example for you guys to mull over:

cooker cct has r1+r2 of 0.18 and and efli is 0.86
lighting cct has r1+r2 of 1.58 and efli is 2.06
Socket cct upstairs has the following:
L-L - 1.16
N-N - 1.17
CPC - CPC - 1.54
R1+R2 - 1.06
efli - 0.96

I would have expected R1+R2 to be lower then 1.06? for a start and efli to be slighty higher maybe I am looking to much into this?

 

[Guest123]

Well by calculation from the end to end readings, R1+R2 should be about 0.67

If anything I would have ordinarily expected the measured loop impedance to be lower taking into account parallel paths and the like.

Seems maybe the unusually high Ze on the PME is an indication of a problem on the line causing spurious readings???

 

[Monkey1984]

Well by calculation from the end to end readings, R1+R2 should be about 0.67

If anything I would have ordinarily expected the measured loop impedance to be lower taking into account parallel paths and the like.

Seems maybe the unusually high Ze on the PME is an indication of a problem on the line causing spurious readings???

I calculated 0.67 as well. All sockets on that part of the house read between 1.01 - 1.06 so i have no reason to believe there is a issue with the integrity of the rfc.

Because this is a PIR should there be any suggestion that further investigation is needed on this circuit? I'm not sure on the best way to note this if it needs noting at all??

As for the Loop impedance - Its a pass in comparison to the tabulated values (1.15 on 32A) but i can see your point on the parallel paths. So I'm not concerned to such an extent.

 

[Guest123]

I'd say as all values fall within limits and are by and large consistent (excluding the Ze) then no comments on the PIR are needed.

Real world situations are often different from those we would expect to come accross in books.

 

[Monkey1984]

Couple more things that were highlighted:

Immersion on Ring main - Protected by Switch Fused spur - Code 4?
Supplementary bonding missing in bathroom - (Metal towel rail in bathroom) - Code 2?
Earth Bonding 6mm on TN-C-S earthing arrangement? - Unsure on that to be honest - Thinking Code 2?

There are signs of supplementary bonding in the downstairs bathroom but not in the upper and the lighting circuits are not RCD protected.

Also on the schedule of Inspections if supplementary bonding is in one bathroom and not the other then its unsatisfactory? Correct?

Sorry for all the questions but been away for a while and want to make sure that everything is correct in my head.