Lead-sheathed wiring – why?

[gerry maddenParticipant @gerrymadden53711]

I found an old book on the shelf about the naval battle with the Scharnhorst. It turned out to be a very interesting read and I was surprised to learn that much of the success of the battle was down to the very capable radar systems installed on the Duke of York. These enabled the ship to track and fire its guns at the enemy even when well out of visual range, a feat which I wasn’t aware existed at the time.

The book mentions how at one point some of the radar was damaged by enemy shells going through the rigging of the Duke. Repairs had to be made subsequently by a young chap climbing the towers (in arctic conditions). The fix involved peeling the lead sheathing off the wires that went up the side of the tower before rejoining the conductors.

In the deepest recesses of my mind I feel I have come across lead-sheathed wiring before, but I just can’t remember where or what the equipment was so I’m a bit intrigued to read the above.

Can anyone clarify what the purpose of the lead sheathing was on the radar cabling? Was it simply just a convenient robust non-corroding flexible material, or did it have some useful electrical characteristics, or both ?

Gerry

[FulmenParticipant @fulmen]

I think it’s as simple as you suspect. Lead doesn’t really have any special electric properties, it’s a pretty meh conductor. It also oxidizes which isn’t great for high frequency radio.

[JasonBModerator @jasonb]

I’ve seen it used for domestic wiring, suppose they did not have PVC back then. I think the red and black inside was rubber

[BazyleParticipant @bazyle]

Few bits around my house still I think, not in use of course. As a child I got most of it to strip the lead for model boat keels.

Probably on the ship it was for shielding from the radar RF as well as being conveniently salt water resistant. I expect inside coper sheathed cable was used in preference to rubber near the radios.

[EmgeeParticipant @emgee]

I can only think it was for electrical shielding.

 

Emgee

[Pete RimmerParticipant @peterimmer30576]

i’ve found it in demolition of old buildings (and even under the floorof my previous house) and I too had wondered why it would have been used.

[Robert Atkinson 2Participant @robertatkinson2]

It was not just on radar or ships. Lead sheathed cable were used in domestic installations in the 1930’s and 40’s. It protected the non to durable insulation and “dressed” nicely for a neat installation. Rodents didn’t like it either.
I’ve always thought that “twin & earth” PVC insulated cable generally has a grey sheath becuase it was originally made to match the old lead covered. The lead was considered superior to the alternative rubber sheathed option. It certainly was in better shape 30 or 40 years later when I came across both durng re-wires. If the PVC had been black customers might think it was the “cheap” rubber type.

On a radar the lead would provide some shielding against electrical noise but it is not the best material for that purpose.

[David JuppParticipant @davidjupp51506]

Where I used to work, some of the older 11kV distribution cables were lead sheathed, paper insulated.

Remember that the polymers we take for granted simply were not widely available at the that time, and certainly had no history of use in cabling.

Polyethylene was very new during WWII, it was key to enabling airborne radar – only saw wider use an insulator in other duties later.

A metallic sheath would give a degree of fire protection.

[Nigel Graham 2Participant @nigelgraham2]

It was indeed common in domestic wiring, with rubber internal insulation.

Our family home into which we moved in 1962 was wired throughout with the stuff. Dad replaced the lot with modern cables and fittings.

As well as removing umpteen feet of iron pipes with screwed connections. The building dated from the 1900s and the pipes were for the original gas-lighting.

Lead does oxidise but only slowly, hence its architectural use on roofs and for a long time, water-pipes; but on a ship it had to withstand salt water spray as well as rain so was suitable there for cable sheaths.

Underground telephone cables, placed within earthenware ducts, were also lead-sheathed over paper-insulated wires. Colour-stripes formed the wires’ identity marks. Jointing these cables required considerable skill, not least in making the wiped-solder joints as on water-pipes.

[peak4Participant @peak4]

Underground telephone cables were lead sheathed, and where jointed, had outer wiped lead joints, much like a larger version of old household lead water piping; think blowlamps, wax, and moleskin cloth wipers.
Lots are still in use today still in the underground copper network, though obviously being replaced with fibre.
The whole cable was then pressurised with desiccated air from each exchange to keep out any water ingress.

Bit of info here on ECP racks (External Cable Pressure); I fitted or moved one or two over the years
https://www.britishtelephones.com/underground/cablepressure.htm

Bill

[Mark EasingwoodParticipant @markeasingwood33578]

Replaced/re-wired some in my Mum & Dad’s house in the late 1970’s, I was still at school, different times!!

They also used wooden back boxes chopped into brickwork/plaster.

I seem to remember the inner insulation was some kind of spiral wrapped canvas type material, it may have been rubberised??

Mark.

[GeorgineerParticipant @georgineer]

Lead was long-lasting, durable and not too expensive.  I have been involved in rewiring various houses and a church where lead-sheathed cable was used, mainly installations from the 1920s.

One advantage, if you took a pride in your work, was that lead sheath was a very passive material and would take and hold whatever curves and flats you shaped it to, unlike tough rubber sheath (TRS) used in the 1930s – give or take – which remains springy when you try to clip it to a wall.

The conductors in lead-sheathed cable were typically tinned copper (3 or 7 strands), rubber coated in red or black, then a cotton braid soaked in red or black ozokerite wax.  The tinning was to stop the sulphur in the rubber from blackening the copper.

As to why lead sheath was used in warships, I would want to ask Dad, who was involved in the design and installation of such things in Portsmouth Dockyard in the 1930s.  Alas, we’re twenty years too late!

George

[Nigel Graham 2Participant @nigelgraham2]

Given we have found it was near-universal for domestic wiring, I wonder if the Naval use reflected its easy availability as well as engineering suitability?

[John HaineParticipant @johnhaine32865]

This was  WW2 battle and shipborne radar was developed not long before and probably installed in a hurry using whatever materials were at hand. Probably not worth trying to overthink the reason. From a maritime p.o.v. putting heavy cable high on a ship isn’t great.

[David George 1Participant @davidgeorge1]

Our whole estate built in the early 1940’s has Lead outer over paper and bitumen covered copper cables for the main house supply. There are many  problems with water getting in to the cables and there are at least one each week somewhere on the state especially when we have had heavy rain. There are joints with a pottery cover filled with bitumen where the connection to each house is.

 

[jimmy bParticipant @jimmyb]

It is still available!

 

Kingsmill Industries sell it for use as lightening conductors.

 

I would put a link, but my phone as ever as different ideas..

 

Jimb

[jimmy b]

On jimmy b Said:

It is still available!

 

Kingsmill Industries sell it for use as lightening conductors.

 

I would put a link, but my phone as ever as different ideas..

 

Jimb

Even though it’s made of lead…

[roy entwistleParticipant @royentwistle24699]

The lead was also the earth as there were only two wires in it

Roy

[jimmy b]

On jimmy b Said:

It is still available!

 

Kingsmill Industries sell it for use as lightening conductors.

 

I would put a link, but my phone as ever as different ideas..

 

Jimb

Permit me : https://kingsmillindustries.com/

https://kingsmillindustries.com/product/copper-cable-lead-covered-stranded/

MichaelG.

…

John is evidently wide-awake this morning 🙂

[SillyOldDufferModerator @sillyoldduffer]

David George, David Jupp, Nigel and others have the answer between them.

Background:  it’s important to insulate power cables electrically and physically and this was hard before plastics were developed.

Early wires were insulated with cotton or silk wrapped around a good insulator, often paper.  Disadvantages many!   Costly to make and install.  High maintenance when it goes wrong or is damaged.   Fails when wet and insects and rodents eat it.  Prone to catch fire and mechanically weak.  Above all, fails miserably when wet!   Water is a problem in ordinary life, and much, much worse at sea.   Rubber improved on paper insulation in some ways, but, like Gutta Percha, Asbestos, Mica, and other insulators has other pros and cons.

The Victorians solved most of these problems by sheathing their insulated cables in Lead.  A good choice, and very common until improved plastics arrived. Lead provides good external protection whilst allowing cables covered in it to be bent round corners etc.  Practical, waterproof, and joints can be soldered to keep it so throughout.  It works!  Many disadvantages though; skills required, cost, weight,  somewhat delicate, and prone to corrosion.  The metal sheath can become Live due to faults.  Not ideal.

Lead sheathed cable ruled from about 1880 to 1945, only starting to fade during the mid-1930s due to slowly improving plastics.  Though plastics rapidly took over after WW2, they aren’t perfect either and I believe Lead sheathing and joints are still occasionally used to protect and seal big underground power cables.

Gerry mentions the Scharnhorst incident required Lead to be peeled off damaged cables.   Our lack of experience with Lead sheathing might cause us to miss that this was an extra difficult repair, much harder than bypassing a run of plastic wire, and important!   Radar being able to tirelessly measure range, bearing and speed at night, in fog, and just over the visual horizon was a huge advantage.  As having inferior or broken electronics loses battles, it was vital to make sure  Scharnhorst was outmatched throughout the fight.

I recommend Friedman’s book ‘Naval Firepower’ to anyone interested in the technology behind aiming guns in wartime.   As individuals firing over open sights rarely hit anything, WW2 was much more sophisticated than Hollywood and propaganda films suggest.  Behind the scenes teams of men operating fiendishly complicated calculators fed information from a host of sensors: optical,  radar, pitch, yaw, roll, speed, wind, temperature, all directed by centralised fire-control.   The men exposed at the gun were vital, but their effectiveness was multiplied by being told where to aim, not at the target they could see, but where it was predicted to be when the shell arrived…

So we have an important Naval battle fought two obsolescent battleships, second but last time battleships fought because battleship technology was extremely vulnerable to air and submarine technologies.  Technology in transition too: Duke of York was fitted with a priced down but state-of-the-art British radar powered by rather old-fashioned lead-sheathed power cables.   Scharnhorst had an expensively well-made German radar past it’s best before date!  Like as not Scharnhorst used lead-sheathed cable for power cables too, anyone know?

An interesting mix of old and new.

Dave

 

 

[peak4]

On peak4 Said:

Underground telephone cables were lead sheathed, and where jointed, had outer wiped lead joints, much like a larger version of old household lead water piping; think blowlamps, wax, and moleskin cloth wipers.
Lots are still in use today still in the underground copper network, though obviously being replaced with fibre.
The whole cable was then pressurised with desiccated air from each exchange to keep out any water ingress.

Bit of info here on ECP racks (External Cable Pressure); I fitted or moved one or two over the years
https://www.britishtelephones.com/underground/cablepressure.htm

Bill

Most of the main trunk cables have been pulled out recently by companies paying BT for the privilege. Filthy job and a lot of empty ducts.

I imagine the Duke of York at 42,000 tons was very sensitive to top-heavyness caused by a bit of lead cable with all those 14″ guns and 14″ thick armour plate.

[Nicholas FarrParticipant @nicholasfarr14254]

Hi, many years ago in my old maintenance job they had a 2″ approx. diameter three phase supply cable, in a gully in the floor of one of the older plants, which was lead sheathed over paper, I think the electricians had to extend the length of it with modern armoured cable, due to some new plant installation, and I believe they used one of those resin filled plastic case packs to ensure a water proof joint.

Regards Nick.

[gerry maddenParticipant @gerrymadden53711]

Thanks chaps. As always, interesting replies with a variety of knowledge and experience.

Regarding the radar on the two respective ships, my book (Death of the Scharnhorst by J Winton) makes the point that the German Navy never seemed to want to trust their radar returns and that was a probably a contributor to their downfall. It’s not made clear why, but this may have been a navy cultural thing. The Duke’s crew however did the opposite. During ‘blind’ shooting they were even able to detect the over-the-horizon splashes of shells that missed the target and adjust their ranging accordingly. This might suggest that the British radar was a little more sophisticated.

Dave, thanks for the heads up on the book Naval Firepower. This could provide many hours of technical thought-provocation, so I may have to invest!

Gerry

[John HaineParticipant @johnhaine32865]

Wikipedia has an excellent article on RN radar from which it seems that the Duke of York had this one fitted:

The 271 it replaced had two antennas so the implication is that this set had 2 x 1 metre antennas up the mast, one Tx and one Rx.  It operated at ~3 GHz so either a largish waveguide or a large diameter coax cable would be needed for low loss assuming that the Tx/Rx were not in the “scanner”.  From the high peak power and frequency it must have used a magnetron which was very new at this stage (1943).  Quite a lot of weight and windage to put on a ship’s mast.  Though the ship’s hull and weaponry are heavy, the guns and armour need to be above the waterline and affect the stability.  Weight higher up has a disproportionate effect on stability as its moment of inertia increases as a square law.

There’s a good book on WW2 German radar – Instruments of Darkness by Alfred Price.  Apparently they had an excellent UHF radar air defence chain working in France, much higher tech than the UK CH system.  But it was run by the Wehrmacht, and all the information on attacking aircraft was fed to Berlin to be shared with the Luftwaffe and might eventually reach the defence forces probably after the planes were gone.  By contrast the CH station operators were in direct contact with the RAF plotting rooms that dispatched the fighters.  One could imagine that similar organisational issues could afflict the way that radar info was used on German ships.

[Don CoxParticipant @doncox80133]

I grew up with lead sheathed cables, helping my father, who was a sparky, pull in new cables using the old lead sheath ones as a draw.  I also had 33 years with BT finishing up in my last three years there managing an underground cable group who had a lot to do with lead sheathed cables and their pressurisation, my previous career. having been mostly maintaining exchanges, didn’t count for much in that job.

My most recent experience with lead sheathed cable was when we came to sell our house four years ago and the estate agent required a certificate for the state of the electrical wiring.  A “Registered” sparky came and pronounced all of my 50 previous years of rewiring and extending in good order, but didn’t like the main earth which was derived from a piece of bonding strip clamped around the lead sheath of the incoming supply cable.  My fault I suppose, I don’t think he would have noticed had I not mentioned it to him.

It is an arrangement which is apparently prohibited by the regulations, the problem lies in that it is not deemed possible to have a reliable clamp on the cable sheath which doesn’t “relax” with time and introduce resistance in the connection. The expert’s suggestion was that I should contact the supplier to see if they could provide a PME earth, I did and they couldn’t, or wouldn’t.  So, after buying a pair of earth rods and driving the two connected together to make 8′ into the ground I got, I seem to remember, 200 ohms compared with the original earth.  I then had to fork out for an 100 A RCD to replace the original incomer, I then had to pay the qualified sparky to fit it.

The house was of mid 1960s vintage and the original cable was supplying it and probably all the other 30 odd houses on the estate in the same way.  I did get to inspect three of my neighbours earthing arrangement and they were exact copies, obviously done by the same person, almost certainly the meter fitter, all those years ago.

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