Bonding water mains

[dnjr]

Dear All
I expect this is going to raise a few eyebrows but..
I know that is your unsure about an earth bond to a water main you can do a continuity test and look for a figure under 0.05 ohms.
I have also read that you can do an IR test, under 23K ohms needs bonding and over 23K does not
Now the thick bit

surely 0.05 is under 23K so why does it not need bonding
when do you use the continuity test and when the IR test

When Ive asked other sparks they just say it is so accept it ( which in other words means they dont know why)
I dont like to just do it because... can anyone put it in simple terms for me

Thanks and regards
dnjr

 

[telectrix]

you bond incoming services as they introduce an earth potential into the property. the IR test for the 23K ohms is to determine if a suspect pipe or whatever is or is not liable to introduce an earth potential.

so say you have a copper cold water pipe in a kitchen. if the water comes in on metal pipework, it's almost certainly extraneous. if ot comes in on plastic, it probably is not. and the IR test will tell you which. i.e. is it connected to earth or not.

 

[dnjr]

you bond incoming services as they introduce an earth potential into the property. the IR test for the 23K ohms is to determine if a suspect pipe or whatever is or is not liable to introduce an earth potential.

so say you have a copper cold water pipe in a kitchen. if the water comes in on metal pipework, it's almost certainly extraneous. if ot comes in on plastic, it probably is not. and the IR test will tell you which. i.e. is it connected to earth or not.

Hi telectrix
Thanks for the prompt reply, its been doing my head in
If I understand correctly
The IR test would only be done if your unsure if the pipe in question need bonding ie if you cant see a bond or it comes in in plastic then changes to copper. if under 23k it needs bonding if over it does not.
If you can see a bond but want to check its complete or good enough you do the continuity and look for 0.05
Is that about it

cheers

 

[Guitarist]

This is really a test an electrician needs to do. It will involve disconnecting the main earth with the supply isolated to carry out the test properly, so I'd rather not explain in detail online for obvious reasons.
GN8 is a must-buy if you really want to understand earthing and bonding properly.

 

[Deleted member 9648]

Dear All
I expect this is going to raise a few eyebrows but..
I know that is your unsure about an earth bond to a water main you can do a continuity test and look for a figure under 0.05 ohms.
I have also read that you can do an IR test, under 23K ohms needs bonding and over 23K does not
Now the thick bit

surely 0.05 is under 23K so why does it not need bonding
when do you use the continuity test and when the IR test

When Ive asked other sparks they just say it is so accept it ( which in other words means they dont know why)
I dont like to just do it because... can anyone put it in simple terms for me

Thanks and regards
dnjr

In a building you are attempting to create a zone of equal potential. In the event of a fault a voltage may appear on parts of the electrical installation/equipment connected to the earthing system until the protective device disconnects the supply. Within the building you are insulated from the general mass of earth and all conductive parts are connected together through a common earthing system,so this fault voltage has minimal shock risk. But a water main or other service may introduce the general mass of earth into the building and hence create a shock risk for a person in contact with the electrical earth and the service during the fault. The 23K test is to determine whether or not the service is introducing the general mass of earth. If it is,and requires bonding,the 0.05 ohm test is to ensure minimal resistance between it and the electrical earth and hence minimal voltage difference.

 

[dnjr]

In a building you are attempting to create a zone of equal potential. In the event of a fault a voltage may appear on parts of the electrical installation/equipment connected to the earthing system until the protective device disconnects the supply. Within the building you are insulated from the general mass of earth and all conductive parts are connected together through a common earthing system,so this fault voltage has minimal shock risk. But a water main or other service may introduce the general mass of earth into the building and hence create a shock risk for a person in contact with the electrical earth and the service during the fault. The 23K test is to determine whether or not the service is introducing the general mass of earth. If it is,and requires bonding,the 0.05 ohm test is to ensure minimal resistance between it and the electrical earth and hence minimal voltage difference.

Thanks wirepuller . very clear much appreciated

 

[t01474]

So if in an old building you had a 6mm water and 6mm gas bond, as long as the continuity between the bond and the incoming main earth is less than 0.05ohms you wouldn't have to upgrade to the recommended 10mm?

 

[Guitarist]

So if in an old building you had a 6mm water and 6mm gas bond, as long as the continuity between the bond and the incoming main earth is less than 0.05ohms you wouldn't have to upgrade to the recommended 10mm?

Errm, it doesn't work like that. The 10mm isn't just about the resistance of the cable.

 

[rattlehead85]

The thing is though, you may have a metal pipe or service entering the building where you are unsure if it is bonded or not. You see a 10mm2 bonding cable leaving the M.E.T but cannot see if or where the bond is connected. You then carry out an IR test between the pipe in question and the M.E.T and the result is less than 23k ohms. But you are still unsure if the bonding is required as the low reading could be due to the unidentified connection present. Very confusing. You could end up running bonding when in theory it is already done.

 

[t01474]

I appreciate that guitarist but as you probably know better than I do, the prevailing opinion of the domestic sparks is 25mm tails, 16mm main earth, 10mm bonds. I know it all depends on the specific circumstances of the house / head / fuse in question, distance of incoming water / gas to the MET , ect

 

[Guitarist]

GN8 is very useful for anyone wanting or needing more details about earthing and bonding

 

[Geoffsd]

The thing is though, you may have a metal pipe or service entering the building where you are unsure if it is bonded or not. You see a 10mm2 bonding cable leaving the M.E.T but cannot see if or where the bond is connected. You then carry out an IR test between the pipe in question and the M.E.T and the result is less than 23k ohms. But you are still unsure if the bonding is required as the low reading could be due to the unidentified connection present. Very confusing. You could end up running bonding when in theory it is already done.

It depends what you mean by 'less than 23kΩ'. I wouldn't call that a low reading.

If you get a value of, say, 20kΩ (don't know how that would be possible if the 10mm² were connected) then you can be sure it needs bonding.

As wirepuller says if the reading is 0.05Ω or less then it's a safe bet it is already bonded - or, if not, doesn't need it.