No main equipotential bonds

[atm84]

There are no main equipotential bonds to water or gas.

What risk does this pose in layman terms?

 

[Simonslimline]

Have you tested to see if they are extraneous?

 

[kenny7askew]

pre cut out break in neutral could lead to harmful voltage on casings of class I equipment,this could be touched at same time as pipes/metal if they are at earth potential-extreaneous

 

[Barry White]

Its purpose is to keep all conductive exposed parts at the "SAME" potential or as close to it as possible so as its bonded to earth if it has a potential because of a fault the earth in the zone should be at the same or close to the potential so reduce or eliminate the risk of a shock.
In layman terms without it a fault could make the pipes live resulting in an electric shock.

 

[happysteve]

In addition to post #3: if they are extraneous, then for the duration of an earth fault (short circuit to earth) - which could be up to 5 seconds for a distribution circuit (or a final circuit over 32A) - the exposed-conductive-parts (bits of metal that are part of your electrical installation, like the casing of class 1 equipment) will be at a different voltage to extraneous-conductive-parts (your water/gas pipes) which is a shock risk.

If RCDs for additional protection are present, the risk associated with the above is significantly reduced... in practice, the RCD will almost certainly trip and clear the fault a lot faster than the OCPD.

 

[Pete999]

There are no main equipotential bonds to water or gas.

What risk does this pose in layman terms?

I refer you to OSG PAGE43

 

[Deleted member 9648]

Its purpose is to keep all conductive exposed parts at the "SAME" potential or as close to it as possible so as its bonded to earth if it has a potential because of a fault the earth in the zone should be at the same or close to the potential so reduce or eliminate the risk of a shock.
In layman terms without it a fault could make the pipes live resulting in an electric shock.

This is incorrect and misleading. The sole purpose of main bonding is to prevent a rise in voltage on conductive parts (read the definition of a conductive part) during a fault, resulting in a shock risk to a person in simultaneous contact with a metallic service introducing the general mass of earth into the property. It's nothing to do with pipes becoming live.

 

[andyb]

Its purpose is to keep all conductive exposed parts at the "SAME" potential or as close to it as possible so as its bonded to earth if it has a potential because of a fault the earth in the zone should be at the same or close to the potential so reduce or eliminate the risk of a shock.
In layman terms without it a fault could make the pipes live resulting in an electric shock.

This is incorrect and misleading. The sole purpose of main bonding is to prevent a rise in voltage on conductive parts (read the definition of a conductive part) during a fault, resulting in a shock risk to a person in simultaneous contact with a metallic service introducing the general mass of earth into the property. It's nothing to do with pipes becoming live.

Arnt you both saying the same thing?

 

[Barry White]

This is incorrect and misleading. The sole purpose of main bonding is to prevent a rise in voltage on conductive parts (read the definition of a conductive part) during a fault, resulting in a shock risk to a person in simultaneous contact with a metallic service introducing the general mass of earth into the property. It's nothing to do with pipes becoming live.

I dont understand I am misleading and you arnt yet we are singing from the same hymn sheet is a pipe that should be bonded not a conductive part? I didnt quote rules or regulations I said it in laymans terms as asked.

 

[Pete999]

All right you have to join the main water and gas pipes with a bit of 10mm earth cable to ensure they are at the same potential as earth.

 

[Hellmooth]

This is incorrect and misleading. The sole purpose of main bonding is to prevent a rise in voltage on conductive parts (read the definition of a conductive part) during a fault, resulting in a shock risk to a person in simultaneous contact with a metallic service introducing the general mass of earth into the property. It's nothing to do with pipes becoming live.

I think he means the pipe would rise to the same potential.

 

[Deleted member 9648]

I dont understand I am misleading and you arnt yet we are singing from the same hymn sheet is a pipe that should be bonded not a conductive part? I didnt quote rules or regulations I said it in laymans terms as asked.

But it's wrong.
A pipe is not a conductive part,a conductive part is a metallic part of the electrical installation which would not normally be live but which may become so under fault conditions. A metallic non electrical service coming into a building from externally is likely to be at earth potential by virtue of being in contact with the general mass of earth,and will remain at earth potential if it is not connected to conductive parts. Explain how a pipe will become live if it is not bonded? If you are going to explain something in laymans terms at least get it right.

 

[Barry White]

It may be at earth potential but is it equipotential to the rest of the earthed metalic electrical instalation. It needs to be kept equipotential in case a fault occurs on an immersion heater etc. Hence they need to be joined.

 

[atm84]

But it's wrong.
A pipe is not a conductive part,a conductive part is a metallic part of the electrical installation which would not normally be live but which may become so under fault conditions. A metallic non electrical service coming into a building from externally is likely to be at earth potential by virtue of being in contact with the general mass of earth,and will remain at earth potential if it is not connected to conductive parts. Explain how a pipe will become live if it is not bonded? If you are going to explain something in laymans terms at least get it right.

You are missing the word 'exposed'. You mean to say 'an exposed conductive part'.

 

[Deleted member 9648]

It may be at earth potential but is it equipotential to the rest of the earthed metalic electrical instalation. It needs to be kept equipotential in case a fault occurs on an immersion heater etc. Hence they need to be joined.

But how does it 'become live' if it's not bonded?

 

[Deleted member 9648]

You are missing the word 'exposed'. You mean to say 'an exposed conductive part'.

Well picked up atm,just given myself a slap.

 

[Barry White]

Yes....but how does it 'become live' if it's not bonded?

in case a fault occurs

 

[Deleted member 9648]

in case a fault occurs

Unbelievable.
And you claim to be an electrical engineer?

 

[Hellmooth]

in case a fault occurs

It isn't even a relevant answer, the question was how would it become live unless it was bonded.......ie if it wasn't bonded it couldn't rise to mains potential.

 

[Barry White]

Unbelievable.
And you claim to be an electrical engineer?

So you think all earths are at the same potential then so you will never get a potential between 2 earth rods spaced apart or a rod and a pipe in the ground at the front and rear of the property.

Dont want to fight would discuss seems if you dont agree, you question who or what I am either discuss with facts or I will ignore you

 

[andyb]

But how does it 'become live' if it's not bonded?

The very fact that it's not bonded could result in a potential between an exposed conductive part and an extraneous conductive part, that extraneous conductive part could be a pipe in a bathroom for example.

If bonded correctly there would be no potential. So not live as you put it.

 

[Barry White]

wrong quote please delete

 

[Deleted member 9648]

Its purpose is to keep all conductive exposed parts at the "SAME" potential or as close to it as possible so as its bonded to earth if it has a potential because of a fault the earth in the zone should be at the same or close to the potential so reduce or eliminate the risk of a shock.
In layman terms without it a fault could make the pipes live resulting in an electric shock.

It may be at earth potential but is it equipotential to the rest of the earthed metalic electrical instalation. It needs to be kept equipotential in case a fault occurs on an immersion heater etc. Hence they need to be joined.

The reason I have gone into argumentative mode is that the sort of statements made above are one of the reasons there is so much confusion on main bonding. The inference is that bonding is there to prevent the pipes becoming live in the event of a live wire/part coming into contact with metallic pipes. This is NOT the reason for main bonding. This is one of the misguided beliefs which leads to people claiming plastic fittings on copper pipework have to be changed to metallic and other such nonsense.

Main bonding is there to negate the effect of a metallic service introducing the reference zero volts of earth into an electrical installation. Without main bonding the effect on a person in contact with an exposed conductive part such as the case of a kettle during a fault, with their hand on a tap would be the same as holding the kettle whilst stood barefoot on wet ground outside.
AT NO POINT IS THE TAP 'LIVE' IF IT'S NOT BONDED.

 

[Barry White]

you have just said what I said quote"Main bonding is there to negate the effect of a metallic service introducing the reference zero volts of earth"
So with your above quote in laymans terms we bond the services to the met so they are at the same potential (you referenced at 0v)

We can go on forever with kettle faults and touching a tap etc. I have seen live taps and showers and theres lots of posts on this forum about them. I work mainly in an engineering enviroment so bet others including yourself have seen more.
If the tap was not bonded and plastic pipe was used the tap would be isolated except for the water in the pipe which would reduce the severity of the shock.
I never said the pipe was live I said it could become live in fault conditions then anyone touching it and an earthed exposed metalic part would indeed get a shock
The plastic fittings is another argument.

 

[Deleted member 9648]

you have just said what I said quote"Main bonding is there to negate the effect of a metallic service introducing the reference zero volts of earth"
So with your above quote in laymans terms we bond the services to the met so they are at the same potential (you referenced at 0v)

We can go on forever with kettle faults and touching a tap etc. I have seen live taps and showers and theres lots of posts on this forum about them. I work mainly in an engineering enviroment so bet others including yourself have seen more.
If the tap was not bonded and plastic pipe was used the tap would be isolated except for the water in the pipe which would reduce the severity of the shock.
I never said the pipe was live I said it could become live in fault conditions then anyone touching it and an earthed exposed metalic part would indeed get a shock
The plastic fittings is another argument.

You miss the point entirely. It is the 'earthed exposed metallic part' as you put it which will experience a rise in potential in the event of a fault between energised conductors and exposed conductive parts,not the pipe.
Main bonding is not there to stop pipes becoming live in the event of faults.
And no,I have never seen a live pipe except on old installations with no earthing system except a suspect water main.
The last 'live pipe' I saw turned out to be a plumber causing a leak which soaked the floor,passing through a hole in the floor was a vermin damaged cable which effectively livened up the pool of water. The plumber kneeling in the water got a belt every time he touched the (unbonded) water main,he assumed the pipe was live when in fact it was the pool of water conducting to a pipe at 0v earth potential.

 

[Barry White]

part quote from wirepuller
"You miss the point entirely. It is the 'earthed exposed metallic part' as you put it which will experience a rise in potential in the event of a fault between energised conductors and exposed conductive parts,not the pipe."

So an immersion heater has an earth fault the tank and pipework are not conected to earth. It will have mains voltage both the tank and the pipework so anyone touching the pipe and an earthed exposed conductive part (metal kettle under no fault) would get a shock it would be the pipe that rose in potential against the 0v of the earthed exposed conductive part.

To try and prevent this we bond the pipework to the met to try and keep it at 0v

quote wirepuller
"The last 'live pipe' I saw turned out to be a plumber causing a leak which soaked the floor,passing through a hole in the floor was a vermin damaged cable which effectively livened up the pool of water. The plumber kneeling in the water got a belt every time he touched the (unbonded) water main,he assumed the pipe was live when in fact it was the pool of water conducting to a pipe at 0v earth potential."

agree with above statment

 

[Deleted member 9648]

part quote from wirepuller
"You miss the point entirely. It is the 'earthed exposed metallic part' as you put it which will experience a rise in potential in the event of a fault between energised conductors and exposed conductive parts,not the pipe."

So an immersion heater has an earth fault the tank and pipework are not conected to earth. It will have mains voltage both the tank and the pipework so anyone touching the pipe and an earthed exposed conductive part (metal kettle under no fault) would get a shock it would be the pipe that rose in potential against the 0v of the earthed exposed conductive part.

To try and prevent this we bond the pipework to the met to try and keep it at 0v

quote wirepuller
"The last 'live pipe' I saw turned out to be a plumber causing a leak which soaked the floor,passing through a hole in the floor was a vermin damaged cable which effectively livened up the pool of water. The plumber kneeling in the water got a belt every time he touched the (unbonded) water main,he assumed the pipe was live when in fact it was the pool of water conducting to a pipe at 0v earth potential."

agree with above statment

Still unbelievable!

For your reason for main bonding to work it would be a requirement for all metallic pipework in a property to be electrically continuous, which goes back to my point about plastic fittings. Have you ever stopped to consider why it is a requirement to main bond at the point of entry? How is that requirement compatible with a pipe connected to the hot tank which has plastic fittings between it and the point of bonding?
It is compatible because bonding has nothing to do with pipes becoming live!

 

[Barry White]

I am out an electrician who has never seen a pipe live and thinks a metalic pipe coming up from the ground is at the same potential as the met going around in circles here.
As for plastic fittings you introduced them to the post that was in laymans terms.
you win I must be wrong

 

[Deleted member 26818]

Here's how I see it:
An extraneous-conductive part may have a resistance to earth of 0.05ohms.
The Ze on a TN-C-S installation may be 0.35ohms, Ze on a TN-S installation 0.8ohms and on a TT installation anything.
This means there will be a difference in potential between the installation earthing and the exposed-conductive part.
Current will flow.
The current could be due to an earth fault in the installation.
However due to the manner our power is distributed there will also be neutral current.
This neutral current will not be just from the installation but will be from any other installation fed from the same origin (sub station).
Equipotential bonding equalises the difference in potential reducing the likelihood of current flowing from the installation earthing to the extraneous-conductive part.

 

[GEOFF S]

Its simples

Forget zero reference, okay. Fault occurs, voltage appears on exposed conductive part. With main bonding in place you transfer a voltage to the extraneous conductive part to limit touch voltage. Thats the purpose of Main Protective Bonding.

Cheers