Whilst we're on the subject of bonding...

[Midwest]

In reply to #39.

Think we all know that water conducts electricity, that's why we have take extra precautions in special locations. However, my understanding of BS7671, is that we are bonding incoming metal pipes, to prevent them introducing potential. I'm not a scientist, but if in the next edtion of BS 7671, they tell me to bond a plastic water pipe, because the water inside can introduce a potential, then I will.

You should google the subject, here is one such piece of research; http://www.plasticpipesgroup.com/media/1036/earthbonding.pdf

 

[Risteard]

Think we all know that water conducts electricity

Actually, water does not conduct electricity contrary to popular belief.

 

[bigspark17]

Actually, water does not conduct electricity contrary to popular belief.

Well im affraid sir your very wrong!

 

[bigspark17]

In reply to #39.

Think we all know that water conducts electricity, that's why we have take extra precautions in special locations. However, my understanding of BS7671, is that we are bonding incoming metal pipes, to prevent them introducing potential. I'm not a scientist, but if in the next edtion of BS 7671, they tell me to bond a plastic water pipe, because the water inside can introduce a potential, then I will.

You should google the subject, here is one such piece of research; http://www.plasticpipesgroup.com/media/1036/earthbonding.pdf

ok playing devils advocat- why do you earth an installation that is copper pipe for water copper gas, but both incoming gas and water pipes are plastic?

 

[Deleted member 9648]

ok playing devils advocat- why do you earth an installation that is copper pipe for water copper gas, but both incoming gas and water pipes are plastic?

You don't.

 

[Risteard]

Well im affraid sir your very wrong!

I'm not wrong. It is a very poor conductor. As I said, it is impurities within water which increase the conductivity.

 

[Leesparkykent]

You would only bond it if it's an extraneous conductive part....a plastic pipe isn't going to be an extraneous conductive part lol.

 

[DPG]

I'm loving the image of 6 inches of copper pipe with a bonding clamp on it Daz

 

[Simonslimline]

This thread is getting silly now.

 

[DPG]

Nothing silly about making sure your water is earthed surely Daz

 

[bigspark17]

I do, you dont!

 

[Leesparkykent]

It amazes me how there is so many qualified sparks out in the field that can't get their head around the subject of bonding lol

 

[Simonslimline]

We all know its a secret dark magic.

 

[davesparks]

Water is not conductive however any impurities dissolved in it will make it slightly conductive.

Experimentation has proved that a 22mm plastic pipe of 600mm length is enough to provide a fully insulated section between 2 copper pipes due to the resistance of the mass of impure water contained within it.

 

[davesparks]

Well im affraid sir your very wrong!

Water is made up of co-valently bonded hydrogen and oxygen atoms with no overall charge so electricity cannot flow through water alone. However that co-valent bond can be broken by a high enough voltage which will release the hydrogen and oxygen atoms in their gaseous form.

The addition of other substances with ionic bonds dissolved in the water results in charged ions being free to move in the water and this electricity can flow although it will have a relatively high resistance.

 

[bigspark17]

If in doubt then insulation test at 500v from MET to part in question <22k ohms bond if not NO NEED! If an installer wanted to he can nothing in bs7671 to say you cant!

 

[DPG]

If in doubt then insulation test at 500v from MET to part in question <22k ohms bond if not NO NEED! If an installer wanted to he can nothing in bs7671 to say you cant!

But you may make the installation more dangerous if you bond unnecessarily. Daz

 

[bigspark17]

But you may make the installation more dangerous if you bond unnecessarily. Daz

Would you care to elaborate on that??

 

[DPG]

Would you care to elaborate on that??

You are effectively making whatever it is that you have bonded a part of the electrical installation. For example, a metal sink - this cannot introduce a potential (even earth potential), and so is not extraneous and should not be bonded. You would not be making things safer by bonding it. Daz

 

[andyb]

1) i wouldnt say that two metallic parts that are 1666 ohms apart are at substantially the same potential, despite our interpretation of reg 415.2.2

2)Thats what i don't understand; - having 1666 ohms between an exposed conductive part and an extraneous conductive part during fault conditions will give a voltage approaching mains - depending on the circuit impedance of course.

cheers

sam

1/ They're not substantially the same Sam. The 1667 is to determine whether bonding is required in the first place. If they were not bonded but the circuits were protected by a 30ma rcd then if the resistance between them was less than 1667 ohms then the touch voltage between the two would be 50v or less, so there would be no requirement to bond.

2/ Not if there's a 30ma rcd, it will trip. If there is no rcd then you do not use 1667, you have to bond regardless.