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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?
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    mapj1:

    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.

     


    One of my concerns about using lead is its low melting point, perhaps when carrying large fault currents. Domestic lead covered cables of old were perhaps fused at 5, 15 or even 30 Amps so fault currents were relatively small. With lead pipes that may carry large diverted neutral currents the lead may melt or or best become soft, so fitting a B.S. 951 earth clamp to a lead gas pipe could be dangerous. I would never do so. Lead melts at about 300 degrees C and copper at over 1,000 degrees C.


    Back in the 40s a device called a "Pyrotip" was used to "Burn" lead for jointing. The manufacturer was the General Electric Company of  Schenectady. The heating source was electrical in the form of a step down transformer to a carbon electrode. The work was connected by a clamp to one terminal and the carbon rod to the other. The p.d. was insufficient to form an arc. The lead was melted only by the power dissipated in the carbon rod and that dissipated in the contact resistance between rod and work.

    So in this case electricity traveling through the rod and lead, was a friend to melting lead, in other cases I am concerned about gas leaking from damaged lead pipes.


    Z.


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  • 0
    mapj1:

    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.

     


    One of my concerns about using lead is its low melting point, perhaps when carrying large fault currents. Domestic lead covered cables of old were perhaps fused at 5, 15 or even 30 Amps so fault currents were relatively small. With lead pipes that may carry large diverted neutral currents the lead may melt or or best become soft, so fitting a B.S. 951 earth clamp to a lead gas pipe could be dangerous. I would never do so. Lead melts at about 300 degrees C and copper at over 1,000 degrees C.


    Back in the 40s a device called a "Pyrotip" was used to "Burn" lead for jointing. The manufacturer was the General Electric Company of  Schenectady. The heating source was electrical in the form of a step down transformer to a carbon electrode. The work was connected by a clamp to one terminal and the carbon rod to the other. The p.d. was insufficient to form an arc. The lead was melted only by the power dissipated in the carbon rod and that dissipated in the contact resistance between rod and work.

    So in this case electricity traveling through the rod and lead, was a friend to melting lead, in other cases I am concerned about gas leaking from damaged lead pipes.


    Z.


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