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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):

    I'll share the Mars bar later! One does need to be a bit careful of many of these internet videos, many of them are seriously odd!

    Kind regards

    David


    Odd in what way?


    Z.


  • 0
    AJJewsbury:
    The diverted neutral currents can be conducted by the armour of the P.I.L.C. cable.

    Not where the steel armour is cut back - as it inevitable is before a cut-out in order to access the lead sheath to make the Earth connection - so for the first few inches at least all the current has to be carried by the lead.

    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.

    But we're talking diverted N currents rather than earth fault currents. I don't know of anything that prevents diverted N currents flowing in lead sheaths of supply cables just as readily as they can flow in metallic water or gas pipes. They're all likely providing metallic paths to neighbouring installations as well as the soil.


       - Andy.


    The video of old showed the steel armour being connected at a joint. I was referring to that underground joint where the armour continuity was maintained.


    I was talking about earth fault currents and the limited magnitude of them flowing in the lead sheath of a P.I.L.C. cable.


    Z.


     


  • 0
    Why do we worry about current in a lead sheath more or less than in a steel armour on a modern cable ?

    I'm not in least worried about the lead cable sheath - quite the reverse - I was trying to demonstrate to Z. that is the service cable is going to be fine the even thicker lead walls of a gas pipe isn't going to be an issue.


        - Andy.
  • 0
    I recently got SSE to replace the service head on an old domestic PILC supply . The old earthing conductor was connected to the steel sheath and had a high Ze (about 1.5 ohm). They stripped back a couple of inches of the steel sheath, exposing the lead, then used a clamp which resembled two copper conduit saddles connected "foot to foot" to connect to the lead. I was surprised that there was apparently no constant-force spring arrangement, and was also left confused as to whether the lead or the steel is the preferred earthing arrangement. I would have asked the fitter some questions, but what with COVID and all,l I just left him to it.
  • 0
    Why do we worry about current in a lead sheath more or less than in a steel armour on a modern cable ? - if anything the lead has a larger cross-section, is better cooled due the larger surface area and and if anything paper and oil not exposed to air is likely to be more robust than XPLE  insulation in terms of failure modes if it heats up.

    I agree once the lead is damaged or not connected, then you have a problem, but that is true of any armoured cable.

    Mike.

  • 0
    The diverted neutral currents can be conducted by the armour of the P.I.L.C. cable.

    Not where the steel armour is cut back - as it inevitable is before a cut-out in order to access the lead sheath to make the Earth connection - so for the first few inches at least all the current has to be carried by the lead.

    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.

    But we're talking diverted N currents rather than earth fault currents. I don't know of anything that prevents diverted N currents flowing in lead sheaths of supply cables just as readily as they can flow in metallic water or gas pipes. They're all likely providing metallic paths to neighbouring installations as well as the soil.


       - Andy.
  • 0
    I'll share the Mars bar later! One does need to be a bit careful of many of these internet videos, many of them are seriously odd!

    Kind regards

    David
  • 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.


    O.K. you win, I'll let you beat me up behind the bike sheds. After viewing this video about the leadlock type water pipe fitting I can see that the lead is quite thick. But you're not having my Mars bar.

    https://www.bing.com/videos/search?q=youtube+gbad+lead+gas+pipe&docid=608025356106101472&mid=492946B69D10B43FF2EA492946B69D10B43FF2EA&view=detail&FORM=VIRE


    Z/


  • 0
    The cold flow of lead can lead to a loose earthing clamp.

    Earthing clamps not to be used on cables | Voltimum UK


    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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