Main bondage

[ultinator]

Does main bonding in every circumstance always need to be under 0.05. main bonding in a house where the main water was moved has 10mm cable but resistance of 0.25 ohms!!>>

 

[D Skelton]

Damn! I opened up this post with 'Bondage' in the title hoping for something else How dissapointed I am.

 

[Guitarist]

it goes in the floow at front of property, (there are 3 x 10mm and 2x6mm, one 10mm being gas) one resurfaces under the sink and terminated there but i couldnt tell you if it is continuous, i mean why would you not run it continuous whenn the extension was being built!! grind my gears this does.&nbsp;<br>It is maybe 10-15 metre run to the water pipe in kitchen. so it obviously shouldnt be that high....so considered that, it isnt acceptable as the run is so short? or is that 0.05 only ever a rough guide. I mean 0.3 isnt really that bad surely??[/QUOTE]

You are joking with this statement I hope...

 

[KAS1]

I know that, but that is not how it's explained in GN3 perhaps that's where people get confused with the 0.05 ohms, apparently that is the most common question people get wrong on testing courses. The max resistance value of a main bonding conductor, we all know it depends on the size of the cable and in this case yes with 10mm that equates to a max length of 27m. However the 0.05 ohms in GN3 refers to testing between any two points such as metallic pipes etc That was my reason for asking which two points he was measuring between.

You are supposed to verify the continuity of the conductor when disconnected so it is all about the csa and length.

A 10mm² copper conductor less than 27m in length cannot be more than 0.05Ω

0.05 is considered negligible - 0.25 or 0.3 is not.

 

[Geoffsd]

It's just that the resistance between two points should be negligible so that there is negligible potential difference between them (in the event of a fault).

0.05Ω is deemed to be negligible as nothing will have a resistance of 0.00Ω.

The fact that this equates to 16m with 6mm², 27m with 10mm² or 43m with 16mm² is not really anything to do with it.
(Although, obviously a 10mm² conductor less than 27m cannot be higher than this and in a 'normal sized' property it will be less.)

If the resistance of the pipe itself (without bonding) to the MET and all other pipes and e-c-ps were less than 0.05Ω then the protective bonding conductor would not be necessary.

 

[KAS1]

I agree with all you've typed. My asking where he was testing to and from, as in his domestic situation it seemed as though he was using the 0,05 ohms as a guide for his expected reading of his bonding conductor, I didn't realise he was trying to determine the length of the bonding conductor.

It's just that the resistance between two points should be negligible so that there is negligible potential difference between them (in the event of a fault).

0.05Ω is deemed to be negligible as nothing will have a resistance of 0.00Ω.

The fact that this equates to 16m with 6mm², 27m with 10mm² or 43m with 16mm² is not really anything to do with it.
(Although, obviously a 10mm² conductor less than 27m cannot be higher than this and in a 'normal sized' property it will be less.)

If the resistance of the pipe itself (without bonding) to the MET and all other pipes and e-c-ps were less than 0.05Ω then the protective bonding conductor would not be necessary.

 

[serpico4321]

Would it not be ok if it satisfied the requirements of R< 50/Ia ? Where Ia is the max current of the protective device? So for 0.3 would be acceptable at 100A

any thoughts?

 

[KAS1]

I ask again where are you getting the 0.3 assuming that's ohms where are you measuring

 

[Geoffsd]

You have to use the current required to operate the 100A fuse 1200 @ 0.4s or 1800A @ 0.1s.
50/ 1200 = 0.04Ω

That's used for supplementary bonding and even there the actual conductor has to be <0.05Ω.

Main bonding conductor conductor must be <0.05Ω.

 

[KAS1]

I think you are getting confused with your Ze measurements, what's the bonding conductor got to do with 100A main fuses?

 

[KAS1]

You must be referring to the Earth Conductor ,,,,,,,,,,,,,,,,,,,

 

[Geoffsd]

My asking where he was testing to and from, as in his domestic situation it seemed as though he was using the 0,05 ohms as a guide for his expected reading of his bonding conductor, I didn't realise he was trying to determine the length of the bonding conductor.

I don't think he is.

In the original question he says

Does main bonding in every circumstance always need to be under 0.05. main bonding in a house where the main water was moved has 10mm cable but resistance of 0.25 ohms!!>>
I don't think the length has anything to do with it apart from the physical impossibilities.

 

[KAS1]

Why is he now quoting 100A fuses lol

- - - Updated - - -

I give up...........

 

[KAS1]

must be getting the wrong end of the stick here lol

 

[Geoffsd]

He's using the formula for whether (supplementary) bonding is required but using the wrong numbers.

See above post.

 

[KAS1]

That's the first time supplementary bonding has been mentioned, as I said where did he get his ohmic value for his main bonding from, where has he measured it to and from............................It's main bonding he has referred to in his question..... did he measure between two pipes, one end of a cable to another, a pipe to a cable I ask again where???

He's using the formula for whether (supplementary) bonding is required but using the wrong numbers.

See above post.