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bonding a short section of water supply pipe

wallywombat
In a victorian terrace house, a lead water supply pipe enters the damp cellar, runs about a meter along the wall to the main brass stopcock, then converts to plastic pipe before exiting the cellar to the rest of the house (which is likely to be a mixture of copper and plastic). The stopcock is a couple of feet away from the CU. Should the supply pipe be bonded? My feeling is no, but I'd be interested in other opinions.


While I'm on the subject, a more general question. Why must any bonding be done after the main stopcock? For example where the supply tees off immediately after the stopcock, is it better to bond one of the tees, or bond just before the stopcock? Where there is a long run of supply pipe before the stopcock, is it better to bond after, with a long MPBC run back to the MET, or bond it near the MET even where that's before the stopcock?
  • 0
    davezawadi (David Stone):

    Ridiculous! Copper is softer than Lead Z, particularly if recently annealed. So I assume you don't bond copper pipes either, particularly as they are much thinner walled? The diverted N current to melt a 1" gas pipe would need to be several hundred Amps to melt it!


    The copper versus lead hardness table.

    https://en.wikipedia.org/wiki/Hardnesses_of_the_elements_(data_page)


    Z.


  • 0
    When?

    When these diverted N currents you're worrying about are trying to make their way back to the star point. They're just as likely to try and get there via the lead sheath of a cable than a gas pipe (probably more so these days as most gas mains have been replaced by plastic).


    BTW around here most earths are connected to the lead sheath by a pipe clip of some kind - the old YEB didn't seem to like hot works and appeared have their own not quite BS 951 variant. There's loads of PILC still in service (often upraded to 80A or 100A fuses too).


      - Andy.
  • 0
    Notice in this clip that jointing involves molten lead

    It'll be solder rather than lead (a lead alloy, but with a much lower melting point).


       - Andy.
  • 0
    AJJewsbury:
    Notice in this clip that jointing involves molten lead

    It'll be solder rather than lead (a lead alloy, but with a much lower melting point).


       - Andy.


    That's presumably why the earth wire was mechanically attached reliably before soldering, so that it was not relying upon just the solder.


    Z


  • 0
    In this clip the main purpose of the  lead is to keep out moisture from the paper insulated conductors. The main earthing function is afforded by the steel wire armouring.

    https://www.bing.com/videos/search?q=youtube+lead+cable+jointing&docid=608039387761899831&mid=8D8D7C492025BAC14F038D8D7C492025BAC14F03&view=detail&FORM=VIRE


    Z.
  • 0
    Whilst those numbers are correct for Brinell hardness they do not really relate to the case. They are obtained by pressing a 4 sided diamond into a thick block of the material with a known load and measuring the depression. The reason I said that annealed copper was softer is that the thin sections used in pipes behave by deflection not much dependant on the hardness, but the material modulus. A BS951 clamp cannot apply enough force to deform a lead gas pipe (about 4-5mm wall) very much, whereas a 0.8mm thick copper one (particularly if soft annealed like microbore pipes or well heated and cooled larger ones). The clamp itself is designed to spread the clamping force around much of the pipe diameter, and generally prevents very much deformation of the circular shape which is inherently very strong (think of bridge arches). I think your fears are groundless, but you may care to try it one day when you find an odd bit of lead (although often a harder alloy called compo in times past) pipe. The wide ranges of the number for Brinell hardness are caused by the wide range of tempers of the material, depending on mechanical and heat treatments before you get it. Take aluminium alloys, for example, T6016 which is used for many purposes including aircraft. Its strength (or stiffness) can be varied across a wide range by heat treatment, the strongest and stiffest being T6016-T6. The same annealed correctly is very soft and easily bent, the -T6 is very stiff indeed. Neither copper or lead pipe will be punctured by mechanical deformation unless very severe, the copper being the most susceptible because it work hardens and becomes brittle.
  • 0
    sweating a joint onto lead pipe or cable is out of fashion, but is a pretty robust.technique.

    Electrically you need perhaps 5 or 6  times the CSA of the copper to be covered with solder to ensure that the fusing current is not an issue - so a 1mm core needs to be immersed in solder for a couple of mm of length (think of the outside of the area of the cylinder of contact, being pi times diameter times immersed length..)

    For mechanical reasons you normally need a lot more than that, and to stop it moving during soldering you would normally bind or clamp the parts. Fine wire bindings  used to be used to hold parts like tin plate covers  and got left submerged in the solder.

    The exception is electronics of surface mount components where the solder alone is the mechanical fixture, as the surface tension is high enough to do this, but contact  area to weight ratios mean this is not applicable to larger devices, or things like switches or terminals where external forces greater than the self-weight are expected, these remain through hole fitting.

    There is a parallel weight and surface tension thing with  small insects that means they can walk on water but elephants can't.


    The problems of unsprung clamps on lead is that the stuff creeps over time and works loose, and clamps fitted by unskilled hands for things like PILC, where the lead is much thinner than lead water pipe,  that the lead is torn or other cable damage is unwittingly caused, but this is a mechanical not an electrical concern, at least until the mechanical damage causes a short to a core.

    Mike.


  • 0
    AJJewsbury:
    When?

    When these diverted N currents you're worrying about are trying to make their way back to the star point. They're just as likely to try and get there via the lead sheath of a cable than a gas pipe (probably more so these days as most gas mains have been replaced by plastic).


    BTW around here most earths are connected to the lead sheath by a pipe clip of some kind - the old YEB didn't seem to like hot works and appeared have their own not quite BS 951 variant. There's loads of PILC still in service (often upraded to 80A or 100A fuses too).


      - Andy.


    The diverted neutral currents can be conducted by the armour of the P.I.L.C. cable.


    For a domestic P.I.L.C. service cable, the earth fault currents will be limited in size by the protective device, say a 30 Amp fuse wire. So the lead will not have to carry hundreds of Amps. as it may for a lead gas pipe.

    IET Forums - PILC Earth Clamp (theiet.org)


    Z.

     


  • 0
    Back in the late 1800s a company called Felten & Guilleaume made a lead covered electrical cable. The inner insulation was an thick  impregnated fibre which occupied about a third of the cable volume. The cable had TWO outer coverings of lead to keep out moisture. Over this was  jute with an impervious compound. Over that was an iron ribbon. The final outer had another layer of impervious compound. 


    Mention is made of dry paper being used as an internal insulator with outer lead to keep out moisture which would destroy the insulating properties of that cable. A pin hole could destroy that cable. Perhaps that is the forerunner of oil insulated cables?


    Z.
  • 0
    davezawadi (David Stone):

    Whilst those numbers are correct for Brinell hardness they do not really relate to the case. They are obtained by pressing a 4 sided diamond into a thick block of the material with a known load and measuring the depression. The reason I said that annealed copper was softer is that the thin sections used in pipes behave by deflection not much dependant on the hardness, but the material modulus. A BS951 clamp cannot apply enough force to deform a lead gas pipe (about 4-5mm wall) very much, whereas a 0.8mm thick copper one (particularly if soft annealed like microbore pipes or well heated and cooled larger ones). The clamp itself is designed to spread the clamping force around much of the pipe diameter, and generally prevents very much deformation of the circular shape which is inherently very strong (think of bridge arches). I think your fears are groundless, but you may care to try it one day when you find an odd bit of lead (although often a harder alloy called compo in times past) pipe. The wide ranges of the number for Brinell hardness are caused by the wide range of tempers of the material, depending on mechanical and heat treatments before you get it. Take aluminium alloys, for example, T6016 which is used for many purposes including aircraft. Its strength (or stiffness) can be varied across a wide range by heat treatment, the strongest and stiffest being T6016-T6. The same annealed correctly is very soft and easily bent, the -T6 is very stiff indeed. Neither copper or lead pipe will be punctured by mechanical deformation unless very severe, the copper being the most susceptible because it work hardens and becomes brittle.


    I did read some time ago about an apprentice that tightened a B.S. 951 earthing clamp on a copper pipe so tight that he punctured the water pipe.


    Z.


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