Main Equipotential Bonding

Discussion in 'Electricians' Talk' started by havenago, Dec 21, 2004.

  1. havenago

    havenago New Member

    Where should the Main Equipotential Earth cable terminate if the mains water stop tap is effectively isolated by one of those plastic surestop water switches?

    The plastic supply pipe is fitted with a metal stop tap which has a 600mm copper run to a plastic sure stop water switch to the house copper. Should the Bonding be after the sure stop or before? (bonding across the plastic obviously)
     
  2. teckie

    teckie New Member

    The main bonding should be within 600mm of the stopcock on the comumer side. The Surestop valve could be deamed a stop cock and you could put it after that. However as there is 600mm between the stopcock and the Sure stop valve that could be thought to be over 600 mm from the proper stopcock. so what I would do is do a continuous bond between both. Strip back part of the cable a couple of feet from the end (Some put a crimp on too)bond either side fo sure stop.
     
  3. cpc

    cpc Member

    Reg 547-02-02.

    cpc
     
  4. Rabbit Rabbit

    Rabbit Rabbit New Member

    Hey cpc your not CPW are you?
     
  5. Damocles

    Damocles New Member

    A reply so succinct as to be devoid of all meaning cpc.

    So you reckon to bond across the second stopcock. Bit of a fudge. What happens when there is next a further length of plastic pipe or a plastic insulating bend after another 50cm.. and then another...and another? Going to bond the lot? No, I don't think so.

    It seems to me that the regulations infer you should bond a convenient copper section as close as possible to the entry point to the building, before the supply splits, and forget the rest.

    The objective is to prevent extraneous voltages entering the building. My logic is that if you have cross-bonded one section at the source, then it is not possible for any later section within the building to introduce anything..job done.
     
  6. Rabbit Rabbit

    Rabbit Rabbit New Member

    Interesting....

    In days of old when Knights were bold and women....

    When ALL electrical supply was TT, they used the water pipe supply, as that was already there, as an earth point.

    The water companys got all upset at this, as they do on TT, and said "Oh you electrical company hands off our kit".

    So electrical company said OK up yours we will shove a rod in the ground then.

    Then in 1854 some geezer from some new outfit called the IEE said "Rollox to that, my mate Faraday says that there needs to be equal potential, I know let's called it 'equipotential' (tm) (c)1854".

    So all the pipes INSIDE the house are at the same potential. Ya a clever old git says IEE to Faraday - "I know we will call it Faraday's Cage in memory of you..
     
  7. Sparkitus

    Sparkitus New Member

    As you are no doubt aware, equipotential bonding earths your copper pipe in the property, not sources an earth as used to be the common misconception. An Electrician a
    earthing/bonding your house would terminate the bond at the first piece of copper on the consumer’s side. Do this and you’ll be fine.
     
  8. Sparkitus

    Sparkitus New Member

    I hadn't read Rabbit Rabbit's concise reply before posting mine...We say the same thing, only he more eloquently....
     
  9. l00pd0g

    l00pd0g New Member

    However, TT supplies are few and far between now.

    Equipotential bonding is to stop extraneous voltages entering the property, as said.

    But, if the only plastic pipe was close to the main stop tap (in this case a plastic stopcock) then I would bond across it, as this will protect the pipes within the fabric of the building and give protection against indirect contact.

    Andy
     
  10. Sparkitus

    Sparkitus New Member

    To explain the point further;

    If this is taking the ****, I'm sorry.

    The point of Equipotential bonding is to provide an equal potential!

    An example:

    You have an old fasioned metalic plug in kettle with the power lead pernamently connected. You reach across to the cold (or hot) tap to fill it.

    Unfortunately my Nan wired up the plug top and you have a live to earth fault that introduces 240v (240v?) to the metal handle.

    The house was wired by Handyandy (sorry mate) so all your earthing is sound. The potential voltage (240v) shorts from the phase to the earth...through the plug to to the earth...via the socket outlet that is terminated on the earth (cpc) terminal at the distribution board...that is also connected to your 10mm2 to your water supply. The pipes under your sink are cross bonded so the hot, cold and metal sink are now at the same potential (as your faulty kettle that my Nan wired up) -an equal potential, no current = happy days, you're not dead!

    Easy as that!
     
  11. l00pd0g

    l00pd0g New Member

    ok, try this example:

    Silly next door neighbour does not have any means of earthing in her house.

    One day, a fault occurs under the floorboards and a live wire touches her cold water pipe.

    The voltage passes down her water pipe, goes underground and then enters your house.

    Luckily, you have earthed your cold water incomer back to your consumer unit and so the voltage will find its way back to the supply transformer and you won't die when you go to run a nice hot bath.

    Andy
     
  12. Sparkitus

    Sparkitus New Member

    Nahhhh,

    Equpotential bonding does not have anything to do with your next door's wiring or for that matter Freddie Mercury's, it's only about providing an equipotential in the installation you are concerned with! Also if your water supply is in lead, the fault current will go directly to earth rather than making it's way through to your house (via you) to find an earth!
     
  13. l00pd0g

    l00pd0g New Member

    Also if your water supply is in lead, the fault current will go directly to earth rather than making it's way through to your house (via you) to find an earth!

    And how do we test this so as to clarify that the fault current will be large enough to operate the protective device?

    Andy
     
  14. Sparkitus

    Sparkitus New Member

    I'm guessing you're taking the **** now?
     
  15. Sparkitus

    Sparkitus New Member

    Ever heard of an Earth Rod?
     
  16. l00pd0g

    l00pd0g New Member

    And also, if equipotential bonding is NOT to protect against extranious voltages, then it would be safe to say that an installation with metalic incoming pipework and plastic internal pipework would NOT need to be bonded at the supply.

    Of course it needs bonding. But why?

    I would say it's to protect people living in the house from getting a belt from the little stub of copper. But most importantly, it's to reduce the resistance of the fault path back to the supply transformer as much as possible so that it will blow the old ladies fuse next door 'cos she didn't have any earths in.

    Andy
     
  17. l00pd0g

    l00pd0g New Member

    Ever heard of an Earth Rod?

    Yes

    Andy
     
  18. Sparkitus

    Sparkitus New Member

    Morning,

    And also, if equipotential bonding is NOT to protect
    against extranious voltages, then it would be safe to
    say that an installation with metalic incoming
    pipework and plastic internal pipework would NOT need
    to be bonded at the supply.

    Of course it needs bonding. But why?

    In your example you would have to bond. You would have a small section of metallic pipe work on the consumer's side where it was jointed from the lead to the plastic. Almost seems a little pointless to bond it, but it is an extraneous conductive part.

    If you altered your example a little and replaced the incoming main with plastic, you would not have to bond.

    I would say it's to protect people living in the
    house from getting a belt from the little stub of
    copper. But most importantly, it's to reduce the
    resistance of the fault path back to the supply
    transformer as much as possible so that it will blow
    the old ladies fuse next door 'cos she didn't have
    any earths in.

    Dependant on the type of supply, the path back to the sub station is provided via either; the metallic sheath of the supply cable, the combined Neutral & Earth (PME) or an earth electrode (rod) installed by the Electrical Contractor. The equipotential bonding plays no part in providing a path back to the transformer. This is further demonstrated when you consider a scenario where the incoming main is of plastic construction.

    Sorry for my previous post of 'ever heard of an earth rod', it was uncalled for.

    Here is the Reg's definition of Equipotential Bonding:

    Electrical connection maintaining various exposed -conductive-parts and extraneous-conductive-parts at substantially the same potential.
     
  19. cpc

    cpc Member

    Hey cpc your not CPW are you?

    If you had come to the xmas p* up you would have found out.

    cpc
     
  20. AceJas

    AceJas New Member

    So how does all this relate to supplementary bonding then?

    I have been picked up on bonding requirements by an inspecting engineer where the installation in the building has various sections of copper pipework with various plastic bits. They made me bond across plastic fittings near the stopcock, and also said that what had been installed as supplementary bonding (in 6mm cable) had to be upgraded to 10mm as the pipework was not electrically continuous with the incoming main.

    I always thought that the pipework was bonded to ensure a low resistance fault path to earth, and hence disconnection via the protective device within the prescribed time. The bonding conductor being sized to ensure that the maximum PSCC can be discharged without melting the cable.

    The example give earlier with the dodgy kettle just makes no sense - if the handle becomes 'live' because your nan put the plug on, and you reach for the earth bonded tap/sink then the path to earth is through you and that will hurt! In this case, if the sink and pipe were not bonded and were isolated from earth, you might still stand a chance if you've got rubber soles on and aren't standing in a puddle of water.

    Have I got this right, or got it round my neck?
     

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