SparkyNinja Webinars

[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

 

[Pete999]

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

no problems with that statement, what is the query?

 

[pc1966]

I think everyone is happy with "of the order of 0.05 ohm or less" as a reasonable test of stuff bonded with moderate cable lengths.

But not when it is turned in to the belief it must be less than 0.05 ohm!

 

[Pete999]

I think everyone is happy with "of the order of 0.05 ohm or less" as a reasonable test of stuff bonded with moderate cable lengths.

But not when it is turned in to the belief it must be less than 0.05 ohm!

Install a larger main bonding conductor.

 

[Mark Wright]

Install a larger main bonding conductor.

Well I think that was the question raised by one member do you have to have a reading of 0.05 and if you exceed this because of a long run do you need a larger CSA?

But I'm getting a headache so i'm off

 

[davesparks]

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

And when you asked the tutors why it had to be 0.05 what did they give as the reason?

Or do you just blindly accept such things without seeking to understand the science behind it?

 

[gazdkw82]

And when you asked the tutors why it had to be 0.05 what did they give as the reason?

Or do you just blindly accept such things without seeking to understand the science behind it?

I donr blindly accept anything. I asked the question.

It's not understanding the science behind the 0.05ohms threshold that is the main question here?

we are trying to determine how this figure is being treated.

I understand the science but I was still wrong in my understanding of what to do when this figure Is not satisfied.

That's what we are trying to accertain

 

[Pete999]

Well I think that was the question raised by one member do you have to have a reading of 0.05 and if you exceed this because of a long run do you need a larger CSA?

But I'm getting a headache so i'm off

Already got one Mate

 

[Mark Wright]

maybe I'm wrong but on his latest video he talks again about taking prospective short circuit current at the end of a circuit and I don't think this is right? it's not the same as an earth fault if a fault starts drawing too much current then the device will trip even if it's a long way away PSCC is only need a the source.

Line and Neutral unlike CPC are the same size conductor.

If it was a long run with then there would be volt drop on both line and neutral, your not going to have a bigger Neutral than your Live are you.

edited sorry pscc

 

[Spoon]

I've only seen some of the Webinars on Youtube.

 

[davesparks]

.
your not going to have a bigger Neutral than your Live are you.

Yes you are if you've have third order harmonics to deal with, the neutral will be oversized to deal with it.