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!!>>

 

[Silly Sausage]

You've either got a very long cable, bad connection, un-zeroed leads or bad contact when testing.

 

[Jonny66]

As Archy says, very long meaning greater than 27m I think it is..........

 

[ultinator]

it is an existing bonding cable, was gonna change the board for an assessment but now i'll need this to be sorted. p.s. the cowboy who installed this bodged quite alot so dunno what is going on

 

[Jonny66]

Back to your original question does it have to be <0.05ohms......Im not so sure now, I think it is only a recommendation as dont think there is a Reg No but not too sure.....although your reading is very high and is probably due to what Archy has stated

 

[Chr!s]

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!!>>

No, hth

 

[Silly Sausage]

If the install is a hatchet job, can you inspect the full length of the cable?
It might have a crappy joint in it somewhere.

 

[Jonny66]

hth......was trying to work out if this was a spelling mistake or some abbreviation......hope this helps.....god Im slow.

 

[MarkieSparkie]

There is no limitation on the resistance (or length) of bonding cables, 0.05Ω is just a suggested ball figure (GN3) to prove the cable 'continuity'. However your reading suggests you have a cable of approximately 137m, very unusual in a domestic installation, but never the less, if correct it would conform to BS7671:2008+A1:2011. If this is not the case your test method or connections are faulty and retesting is advisable. In which case if retesting reveals a similar resistance, further investigation and/or replacement would be necessary as it's likely you don't actually have a continuous length of 10mm[SUP]2[/SUP] cable.

 

[monkeyelectric]

I would check its 10mm for the whole run and not run into a cavity, terminated to 4mm then back to 10mm where it exits the cavity, seen this done before

 

[Toby Kuhnert]

the 0.05 ohm reading comes from [guidance note] 3, and it is just that, a guide.

 

[ultinator]

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??

 

[DJ Ovengloves]

This thread is much duller than I was hoping. Anyone got the phone number of trading standards?

 

[KAS1]

Between which two points are you measuring to obtain the reading of 0.25 ohms, the measurement of 0.05 ohms is nothing to do with the length of the main bonding conductors as I see it

 

[Geoffsd]

, the measurement of 0.05 ohms is nothing to do with the length of the main bonding conductors as I see it

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.

 

[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.