SparkyNinja Webinars

[SparkyChick]

Hi all,

SparkyNinja is running some webinars, you can check them out here:-

SparkyNinja Webinars

sparkyninja.com

I think there will be more added to the list as it sounds like he's got some planned for next week as well.

 

[Mark Wright]

I've only just started watching and got some answers I've been looking for.

I turned off as soon as they started banging on about testing main protective bonding conductors and that they have to be no more than 0.05 ohms. They are as bad as the training providers they slag off by which I mean providing incorrect information to the masses but refused to acknowledge my questions regarding how they came to that conclusion.

"In order to achieve this it is recomended that the resistance of the bonding conductors doesn't exceed 0.05Ω. Chapter 54 of BS 7671 covers the requirements of protective bonding. Chapter 4 of the On-site Guide is also useful....."

Quote Chris Kitcher

 

[Ian1981]

I've only just started watching and got some answers I've been looking for.


"In order to achieve this it is recomended that the resistance of the bonding conductors doesn't exceed 0.05Ω. Chapter 54 of BS 7671 covers the requirements of protective bonding. Chapter 4 of the On-site Guide is also useful....."

Quote Chris Kitcher

There’s no requirement or regulation that states that a protective bonding conductor has to be or must not exceed 0.05 ohms.
This has been done to death on this forum and is a common misconception within the industry.
Chapter 54 gives sizes for protective bonding conductors but nothing about their lengths/maximum resistance because they are not limited by length.
The measured R2 reading from the MET to the bonding conductor should reflect its length or if unknown, an engineering judgment made for the effectiveness of the connection/conductor taking into account its CSA.

 

[Mark Wright]

GN3

"When testing the effectiveness of main equipotential bonding conductors, the resistance value between a service pipe or other extraneous-conductive-part and the main earthing terminal should be of the order of 0.05 ohm or less"

Basically To exceed 0.05 you would have quite a long if you've used the correct CSA a negligible resistance should exist i.e 0.05.

 

[Ian1981]

GN3

"When testing the effectiveness of main equipotential bonding conductors, the resistance value between a service pipe or other extraneous-conductive-part and the main earthing terminal should be of the order of 0.05 ohm or less"

Basically To exceed 0.05 you would have quite a long if you've used the correct CSA a negligible resistance should exist i.e 0.05.

GN3 is not a regulation tho may state regulations from bs7671, it’s a guidance note only and does not overrule or exceed a British standard, that said it is an excellent book for inspection and testing guidance.
Now read the rest of that extract from GN3.
It states that the 0.05 value is NOT from the MET to the bonding conductor, it is a measurement between pipework that is ‘built in’ so a reading in the order of 0.05 ohms can be assumed to mean that the pipework is effectively connected together by a suitably low impedance in the order of say ‘0.05 ohms’ when testing between pipework.
Now go read chapter 54 protective bonding conductors and the regulations which state the CSA required for PME and non PME conditions and tell me where it states that a CSA should be increased if you go over a value of 0.05, which appears nowhere within bs7671?

 

[Mark Wright]

"A satisfactory test result for the bonding conductors will be in the order of 0.05"
Quote "Trevor Linsley"

anyway it doesn't matter if your getting over 0.05 ohms you probably have a very long run if not you should investigate, As I question the clarity on the subject of Bonding and Earthing in BS7671 i'm not defending anything or anything but seems 0.05 is a rule of thumb type value.

and it's from the MET to the furthest point.

 

[Ian1981]

Long runs can occur, especially in non domestic installations but like you say ,that doesn’t make it unsatisfactory.
Ive no idea who Trevor Linsley is but you can’t quote someone and think that it overules the requirements of the regulations.
0.10 ohms could also be considered a satisfactory test result, so that 0.05 is just a blanket statement really and holds no relevance when discussing continuity readings of protective bonding conductors, could be more, could be less.

 

[gazdkw82]

It's interesting, as a recently qualified electrician, this value was drilled into students.

Also, when I did 2391 it was seen as the value you cannot exceed.

I just assumed it could never be exceeded in any circumstance

 

[pc1966]

It is probably one of those "rule of thumb" figures that has been adapted as a pseudo-regulation. I guess that 0.05 ohms is around 27m of 10mm cable and the majority of installations would be shorter so it is a simple "Is this bonded?" test and easy to put in guidance notes, etc.

But as other have said many times, the 0.05 ohm is not a regulation. They only give the minimum CSA, max Z, etc, needed to be acceptably safe!

 

[telectrix]

the 0.05 figure is the max. between a bonding conductor and the pipe it's bonded to.i.e. it just prves that the conductor is effectively connected (electrically) to the pipe, rather than the clamp being fitted onto a painted pipe for example.nothing to do with the resistance of the cable itself. top of my head, a 10mm conducter approx. 30m in length would be 0.05 ohms.

 

[Ian1981]

It's interesting, as a recently qualified electrician, this value was drilled into students.

Also, when I did 2391 it was seen as the value you cannot exceed.

I just assumed it could never be exceeded in any circumstance

There’s a YouTube training provider GSH electrical , good educational videos, hearts in the right place etc but on one video he suggested that if 0.05 is exceeded then a 16mm bonding conductor is required, I mean imagine charging a customer for unnecessary work because of your lack of understanding/knowledge and assumptions?
I argued the case on line and as usual the trainers don’t like it.

It’s a good educational channel for apprentices tho.

 

[pc1966]

0.05 ohm and 50V is around 1kA fault current which is about the 0.4s blow time for a 100A fuse. Hmm...can we have a "wooden spoon" emoji for stirring up even more debate?

 

[westward10]

It is easy to get sucked into the whirlpool of YouTube gurus offering their sage advice.

 

[Mark Wright]

There are number of books just by searching that state 0.05 I won't quote them all.

Also look here How long should Main Protective Bonding Conductors be? - https://www.voltimum.co.uk/articles/how-long-should-main-protective-bonding
Questions the length

but it stands to reason as most of the time the consumer unit is right next to the service pipes and with such a large CSA you can go a long distance like 25m before the reading gets higher so if your reading more than a nominal reading on a short run I.e above 0.05 you would question what's wrong wouldn't you? O I've got a run of less than 1 meter and a reading off 1.00ohm that's not right is it, you don't need a reg to tell you that do you.

and if its a very long run above 25m and your getting a higher reading you might question how effective the Bonding is.

but....
the current City and Guilds book says "GN3 states the resistance of the clamp should be in order of 0.05 Ohms........."

 

[pc1966]

What GN3 says on page 45 is:

This method can be used to confirm a bonding connection between extraneous-conductive-parts where it is not possible to see a bonding connection, for example, where bonding clamps have been 'built in'. The test would be done by connecting the leads of the test instrument between any two points, such as metallic pipes, and looking for a low reading of the order of 0.05 Ω, but do keep in mind that such a reading for a single core 6.0mm2 or 10.0mm2 conductor, equates to 15 m and 25 m respectively. (It should be noted that not all low-resistance ohmmeters can read this low, see Section 4.3.) It should be noted that this is not the R2 resistance measured from the Main Earthing Terminal to the bonding clamp or adjacent pipework.

So they are not saying you should see 0.05 back to the MET, only that a reading of that order between metal parts implies they are adequately bonded (or otherwise connected) for the purpose of safety.

 

[Mark Wright]

I'm just putting what the C&G book says but GN3 does also says "When testing the effectiveness of main equipotential bonding conductors, the resistance value between a service pipe or other extraneous-conductive-part and the main earthing terminal should be of the order of 0.05 ohm or less"
Source URL: SparkyNinja Webinars - https://www.electriciansforums.net/threads/sparkyninja-webinars.184880/

but with the Regs and OSG you can measure the length and do the Maths and generally you would be within 0.05