Naked Ladies? the results for L-L and N-N should be within 0.05 ohms

[J.C.E]

pretty sure it says it in on site guide too- for 2.5mm t+e r1 and rn end to ends to be within 0.05 of each other and r2 should be around 1.67x r1/rn.

 

[Pat H]

The regulations have tolerances states designed to ensure safety. If readings are outside those tolerances then something isn't right.
What is being proposed is that either the tolerances are just incorrect and should be ignored. Or they can be ignored if it suits.
You either accept that the readings between 2 equal conductors should be the same o r that not being so isn't an issue.

But we know that unexpected resistance isn't right. Its a fault. Will that resistance remain stable under all circumstances? How can we know unless we know what's causing it.
So with a higher resistance reading than tolerance allows we are assuming it will remain at that level. And we can't assume that. under load it may increase. if caused by water ingress it may increase. Increased resistance could generate heat at that location.
that could lead to a fire. And we can't say it won't because we have no idea why its happening until we investigate and resolve it.

if I'm on a job I'm responsible for the safety of the installation and its not even fair to ask a customer if they want to pay for safety unless its a risk you can identify and relate to the customer in terms they will understand.

That's my view but accept others will differ in theirs.

 

[Midwest]

OSG does suggest a figure of 0.05 ohms, GN3 states 'the resistance values obtained should be of the same order......'. I can obtain a difference of more than 0.05, if I take a reading with the test leads attached, and then a different reading applying pressure to the clips.

In a new installation, I would expect identical results (r1+rn). In older installations, that tolerance maybe in a higher magnitude. And in older installations, there is more chance deteriorating terminals, inaccessible JB's or unseen diy work. Its what you chose or what the customer chooses to do about it, is the issue.

 

[Startinez]

Typical classroom clown. Wouldn't last 5 minutes in the real world, and wouldn't make a brass farthing either. Midwest has got it right, any continuity is 90% of the way there.......

"Typical classroom clown" - this is exactly how it's taught these days and the 0.05 figure is quoted in GN3. Dismissing advances in technology and teachings, especially in an ever evolving business such as electrics, seems like a silly approach to me.

Edit: 0.05 is quoted in OSG not GN3

 

[sparksburnout]

OSG does suggest a figure of 0.05 ohms, GN3 states 'the resistance values obtained should be of the same order......'. I can obtain a difference of more than 0.05, if I take a reading with the test leads attached, and then a different reading applying pressure to the clips.

In a new installation, I would expect identical results (r1+rn). In older installations, that tolerance maybe in a higher magnitude. And in older installations, there is more chance deteriorating terminals, inaccessible JB's or unseen diy work. Its what you chose or what the customer chooses to do about it, is the issue.

"Typical classroom clown" - this is exactly how it's taught these days and the 0.05 figure is quoted in GN3. Dismissing advances in technology and teachings, especially in an ever evolving business such as electrics, seems like a silly approach to me.

Edit: 0.05 is quoted in OSG not GN3

"Typical classroom clown" - this is exactly how it's taught these days and the 0.05 figure is quoted in GN3. Dismissing advances in technology and teachings, especially in an ever evolving business such as electrics, seems like a silly approach to me.

Edit: 0.05 is quoted in OSG not GN3

You wait until you are out in the real world and see how silly it is. I could take you to a dozen older properties round here and do an RFC test, and guarantee that the R1 and Rn readings would be further apart than 0.05 ohms. are you going to spend hours (days even) pulling up floors and god knows what else in each one? Or are you going to use a bit of common and move on. Its like Midwest says, you can get those sort of differences by jiggling the test leads around. If they are widely different, then yes there is a problem that needs investigation, but not 0.05 ohms. You have to remember that a lot of lecturers have never operated in a real environment. You have to balance what you are taught with actually making a living.

 

[sparksburnout]

I tell you what, I am just off out to do a job adding a couple of sockets to a RFC. I will report back with the readings, who wants to bet they will be further apart than 0.05? I promise to be honest. Its a 1960's job, original wiring. Watch this space......

 

[Startinez]

You wait until you are out in the real world and see how silly it is. I could take you to a dozen older properties round here and do an RFC test, and guarantee that the R1 and Rn readings would be further apart than 0.05 ohms. are you going to spend hours (days even) pulling up floors and god knows what else in each one? Or are you going to use a bit of common and move on. Its like Midwest says, you can get those sort of differences by jiggling the test leads around. If they are widely different, then yes there is a problem that needs investigation, but not 0.05 ohms. You have to remember that a lot of lecturers have never operated in a real environment. You have to balance what you are taught with actually making a living.

I fully understand and actually do agree with you. I'd expect older properties to be quite a way apart from a new installation in terms of readings, I just think the rebuttal of "classroom clown" is a bit harsh seeing as though that is the standard for newer installs.

Ultimately though, if you know it's an older installation and are receiving these sorts of readings then that's to be expected and noted. However, surely there's no harm in stating to the customer that while those sort of readings are expected for an installation of that age, if it were a new install then you'd expect a lot better?

That's where the discrepancy of being experienced comes in. The ability to differentiate between expected readings and new values being taught.

 

[Pat H]

I was taught by an "old Hand" Electrician and his view was that differences could be expected and depending on the size and number of outlets you make a judgement call. But with a difference in reading he'd check all the accessible outlets and junction boxes. If its in a wall or under a floor and access isn't practical then you discuss as mentioned with the home owner and suggest a more regular inspection schedule to monitor if its getting worse or constant.

 

[The Ghost]

I think when the on site guide says 0.05 they are talking about initial verification in a new circuit not EICR on older rewires. So if they were really out like double reading, then you know you screwed up on a connection, but not to worry you should pick it up doing R1/R2 at all sockets.

 

[sparksburnout]

I fully understand and actually do agree with you. I'd expect older properties to be quite a way apart from a new installation in terms of readings, I just think the rebuttal of "classroom clown" is a bit harsh seeing as though that is the standard for newer installs.

Ultimately though, if you know it's an older installation and are receiving these sorts of readings then that's to be expected and noted. However, surely there's no harm in stating to the customer that while those sort of readings are expected for an installation of that age, if it were a new install then you'd expect a lot better?

That's where the discrepancy of being experienced comes in. The ability to differentiate between expected readings and new values being taught.

Your right, I shouldn't have used that term, and I have regretted it ever since actually. Unfortunately I couldn't edit it, the guy in question has written some excellent books a couple of which I own and often refer to. It is just the fact that there is a lot of difference between the classroom environment and the real world, as born out this afternoon! although not too great an example I measured 0.44 for R1 and 0.51 for Rn. Now, I believe that most people, me certainly, would think "1960's property, original wiring, iv'e got a difference here of 0.07, jackpot. As you say, a judgement call would be made depending on how far out it might be if it were higher, but I still think this 0.05 guideline is a bit unrealistic unless it is a fairly new installation. You have to weigh up the time it could take to find and remove all the accessory fronts, the damage you might do in so doing (grouting and so on), the difficulty (under kitchen units with 3 inch screws disappearing into a black hole), and then the likely-hood that it is probably going to be a junction box under an oak wardrobe stuffed to the gills. To say that such things are easily remedied in 15 minutes is utter nonsense, as has been muted.

 

[Andy78]

Your right, I shouldn't have used that term, and I have regretted it ever since actually. Unfortunately I couldn't edit it, the guy in question has written some excellent books a couple of which I own and often refer to. It is just the fact that there is a lot of difference between the classroom environment and the real world, as born out this afternoon! although not too great an example I measured 0.44 for R1 and 0.51 for Rn. Now, I believe that most people, me certainly, would think "1960's property, original wiring, iv'e got a difference here of 0.07, jackpot. As you say, a judgement call would be made depending on how far out it might be if it were higher, but I still think this 0.05 guideline is a bit unrealistic unless it is a fairly new installation. You have to weigh up the time it could take to find and remove all the accessory fronts, the damage you might do in so doing (grouting and so on), the difficulty (under kitchen units with 3 inch screws disappearing into a black hole), and then the likely-hood that it is probably going to be a junction box under an oak wardrobe stuffed to the gills. To say that such things are easily remedied in 15 minutes is utter nonsense, as has been muted.

The descriptions of test procedures and their guidance information in the guidance notes have clearly been written to pertain to initial verification. It would be entirely reasonable to assume perfect readings on initial verification for ring continuity live conductor comparison, and a difference of more than 0.05 would rightly cause me concern on a new circuit.

I do agree that experience plays a huge part in what you would expect to see in older installations, and you can usually have a good guess at the cause of the anomaly. At what level of difference the person testing starts to be concerned is also a matter of experience and opinion.

 

[HandySparks]

The regulations have tolerances states designed to ensure safety. If readings are outside those tolerances then something isn't right.

What part of the regs are you referring to?

 

[VoltzElectrical]

Thanks for all your input. The case in question was a school that had been rewired approximately 5 years ago in twin and earth LSF. A previous electrician with the firm had checked connections in all socket outlets, I was to check in the DB. The DB connections were fine, so I tested again at a socket outlet and got the readings I mentioned. NO JBs that I know of. The job was wired by subbies, not us. With not being able to readily fix the 'fault' I just wanted to gauge how concerned you would be with leaving it at that or recommending further investigation.

Thanks

 

[Flanders]

And what about when it is in some long-forgotten accessory that even the home owner is unaware of, or a JB hidden under the floor, or god-knows where else? 10-15mins???

Then i would put down on the report as a code 3 and move

 

[Tomhw100]

Evening

I've been carrying out EICRs on council properties in Essex for the last five years, in all manner of properties dating back as early as the 1960s and surprisingly some ring final circuits still have sound ring continuity with exactly the same readings. Obviously we do find a lot which are discontinuous and some with r1 and rn slightly different. And discrepancy of 0.05 (which to be honest isn't that common ) I would leave. Any thing higher than that would to me suggest a loose connection which I would look to rectify. Obviously being council owned properties the tenant isn't paying for time anyway!