The strongest findings across the Bell System Technical Journal papers in this collection, grouped by topic. Each paper’s page has its full list in a “Relevance to Lake Tahoe’s cables” box.
Each finding states only what the paper says, in its own words, with page references. The Lake Tahoe side uses only facts already published on this site:
Coverage. 23 findings across 9 papers:
| Paper | Findings |
|---|---|
| Burns 1936 | 6 |
| Buckley 1942 | 4 |
| Gilbert 1951 | 3 |
| Shaw & Fondiller 1926 | 3 |
| Affel 1932 | 2 |
| Hitchcock 1926 | 1 |
| Buckley 1928 | 1 |
| Buckley 1925 | 0 |
| Blackwell 1932 | 0 |
Burns is the only paper about lead’s behaviour. The others mention lead as a material in passing, and two of them have nothing relevant.
1. Lead was chosen for extrusion first and corrosion resistance second.
While the choice of lead as a cable sheathing material was dictated primarily by physical requirements, notably its adaptability to extrusion, corrosion resistance has been a large factor undoubtedly in its successful use.
These are the Bell System’s own reasons for the construction later found in Lake Tahoe.
2. Lead sheathing was standard for Bell telephone cable from the 1880s to at least 1950.
In the Bell System alone there are about 180,000 miles of lead alloy covered cables, about forty per cent of which are underground.
The underground cables have the same coaxial circuit as the submarine cables but in place of the mechanical protection of jute and armor they are provided with electrical protection of helical steel tapes, layers of paper and over all a lead sheath.
This places the Tahoe cables in the Bell System’s mainstream construction of the period. The 1955 lease comes a few years after Gilbert.
3. On the ocean routes in these papers, lead sits at the shore and on land, not on the deep-sea cable.
Heretofore submarine cables having waterproof insulation, with the exception of the Catalina Island cables which are insulated with a special rubber mixture, have almost invariably been insulated with gutta percha, or balata, or a mixture of these substances.
The one paper that pairs lead-covered cable with shallow submerged routes is Buckley (1942, p. 16): “the repeater can be incorporated in lead-covered cables for shallow seas”. So the ocean cables are not direct analogues of a lead-sheathed lake-bed cable.
4. Lead buried directly in soil corrodes seriously, and the soil matters more than the alloy.
Cable sheathing buried directly in soils is seriously corroded by differential aeration-cell action resulting from physical contact of relatively large soil particles and metal.
It will be seen that of the two variables, soil character and alloy composition, the former is decidedly the more important in its effect upon rate of corrosion.
The Bell System’s own practice was not to bury lead-covered cable without a protective coating (p. 607). This is relevant to the Baldwin Beach section under the sand. Burns describes buried cable in general, not that section’s condition.
5. Lead corrodes in soft, low-mineral water; dissolved minerals protect it.
It is well known that lead is markedly corroded in distilled water, and by waters low in hardness and in total solids.
Burns makes water chemistry the deciding factor. This set contains no data on Lake Tahoe’s water.
6. Experience with cables submerged in sea water was favourable.
The favorable experience with cables submerged in sea water or mixtures of sea water and soil waters indicates that corrosion inhibitive agents exert under these exposures a predominating influence.
Burns reports this for sea water and soil waters only, and has nothing on lakes. Neither #5 nor #6 transfers to Tahoe without other evidence.
7. A protective film can preserve lead indefinitely, but only if the environment allows it to form and it is left undisturbed.
Once a protective film has formed on lead the metal may be preserved indefinitely if not physically disturbed.
Whether or not a protective film forms depends largely upon the character of the environment to which the metal is exposed.
8. Corrosion was rare because the plant was actively maintained.
From the description of the occurrence and general characteristics of cable sheath corrosion in the present paper it may be concluded that although there are many conditions under which cables may corrode, the actual incidence of corrosion is small owing to the maintenance of non-corrosive chemical and electrical environments in the cable plant.
Burns also credits “the vigilance of the electrolysis engineers and the plant forces” (Burns 1936, p. 603).
9. Design lives of 10–20 years are for repeater tubes and components, not cable sheaths.
Neither paper gives a service life for a cable sheath.
10. The papers are silent on retired cable. The only removal passage concerns loading coils on overhead lines, taken out so the lines could be reused:
These general transmission considerations are resulting in the removal of coil loading from high grade open wire lines.
Gilbert (1951, p. 68) explains why lifting submerged cable is avoided: it is “expensive and time consuming”, and it disturbs the cable. That describes deep-sea repair, not removal.
This incredible outcome was delivered by a broad range of stakeholders coming together. We’re grateful to AT&T, their 3rd party partners, the 7 government agencies that authorized removal activities, all our petition signers, and the broader Lake Tahoe community. We got the lead out!
Questions? info@tahoelead.com
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