bonding a short section of water supply pipe

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/

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.

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

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.


 

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.

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.