Main bondage

[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.

 

[KAS1]

Sparks are still incorrectly stated that the maximum value for the resistance of a main protective bonding conductor is 0.05 ohms. This value is applicable where access to the bonding connection is not possible and a test is made between two extraneous conductive parts (GN3 Page 35). This value is not the maximum permitted resistance of the main protective bonding conductor.

 

[Geoffsd]

But it's the same value for everything.

As I keep saying - it is a value deemed 'negligible' which is what is required.

There would be even more confusion if GN3 just stated a resistance of negligible impedance between parts must be ensured.

 

[KAS1]

So where did he get the high value from, I don't think he understands what he is measuring, "Does main bonding in every circumstance always need to be under 0.05.NO IS THE ANSWER, main bonding in a house where the main water was moved has 10mm cable but resistance of 0.25 ohms!!" where did he get 0.25 ohms between where and where, does he mean 0.25 ohms between the water pipe and the main bonding cable before they are connected together?????

 

[Knobhead]

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??

Could you translate that in to something like English please.

 

[KAS1]

Thanks tony that has answered my question, he doesn't know what he's measuring...............

 

[ezzzekiel]

if as stated 0.05 is used as a guide as its considered negligable then at what value does it become a prob as if that was the case then a stated value would need to be given in bs7671.

i believe voltage drop (50v safe touch) as in supp bonds plays a part in this - 0.05 ohms is good for 27m ensuring no drop +or- 50v will occur between accessible part.

always been my take on it.

 

[Geoffsd]

if as stated 0.05 is used as a guide as its considered negligable then at what value does it become a prob as if that was the case then a stated value would need to be given in bs7671.

i believe voltage drop (50v safe touch) as in supp bonds plays a part in this - 0.05 ohms is good for 27m ensuring no drop +or- 50v will occur between accessible part..

Yes, that is what serpico raised.

Then, however, as with most things you have to calculate rather than rely on the 'guides' one size fits all

R = 50/Ia - serpico made the mistake of using the In of the 100A fuse.

 

[ultinator]

So as Geoffsd and Serpico said:

for a 100A domestic supply, the Ia value would be either 1200 at 0.4s or 630 at 5s

To which the higher would make the maximum permittable resistance of the main bonding conductor is 0.041 ohms if R< 50/1200

The cable measured was directly from the conductor at the MET to the bonding clamp using croc clips?

So would a resistance of 0.25 Ohms mean that the bonding conductor is unsafe as the resistance is too high in the event of a fault?

 

[ezzzekiel]

Yes, that is what serpico raised.

.

never read the whole post - but thats my opinion also

 

[Geoffsd]

So would a resistance of 0.25 Ohms mean that the bonding conductor is unsafe as the resistance is too high in the event of a fault?

Yes, but if the conductor is continuous it cannot be that high.

Undo it from the clamp and then - if the reading is ok on the wire itself fit a new clamp.

If not - then you will have to find the problem or fit a new conductor.