UNDERGROUND CABLES.

Hauraki Plains Gazette, Volume XXXVIII, Issue 5188, 7 October 1927, Page 4

UNDERGROUND CABLES.

POWER SERVICES ON FARMS. CONSIDERATION BY BOARD. Tlie question of using underground cablq for transmitting electricitj F to farms wgs the subject of some consideration by the members of the Thames Valley Electric Power Board. The matter was brought forward by Mr J. B. Thomas, who contended that the; board should not go ahead too hurriedly with the construction of extensions and new lines until the question of the underground system had been fully explored. Personally he was in favour of supplying farms at least with electricity by the cable system if it was practicable, on account of minimising danger from falling power lines. It, might also be advantageous to use cables on the roadside in many areas, especially where roads were narrow and dangqr was increased on that accoount.

In reply to the chairman (Mr F. M. Strange) the engineer (Mr N. G. McLeod) said that he had alrejady investigated the position and had obtained opinions of different authorities regarding the various classes of cables which might be used for such work. Underground cables were used for general power supply before overhead lines were ever considered, and construction was such that supply by them was very satisfactory and reliable. The cost of supply by underground cablet? was usually very much greater than supply by overhead wires, though there were cases where installation would be less, costjy than overhead wires. Each case required to be considered on its merits, however, although the aesthetic aspect or the security value were; often the determining factors in favour of underground cables. OPINIONS OF MANUFACTURERS. Opinions had been obtained from different cable manufacturers in Britain, knd also from the Hydro-Electric Commission, Ontario. The recommendations of the, manufacturers were not always carried out by supply authorities but spine- of the comment was interesting. The Ontario Power Commission used plain 1, pad-covered conductors in the .country, and lead covering was also used for the neutral or earthed conductor. Tn Britain plain lead-covered conductors were not allowed underground, nqr could the lead she.ath be used as a conductor. T.he lead covering had to be protected by armouring, or else the cable had to be placed in; a suitable trough and a separate conductor used for the neutral. The arguments against using an unprotected lead covering were that the mechanical strength of the lead covering was low, heavily fertilised soil would cause trouble with the lead, arid stones in the soil might come; in contact with the lead and damage it. REGULATIONS IGNORED.

In spite of the regulations, and. apparently without t’ne knowledge of the electricity commissioners, more than one British undertaking bad risked using unavmoured cables. In one case plain lead-covered and waterproofed cables had been in the ground about 'lO years, and were still giving satisfactory service,. The cables were laid at a depth of 12 infeh«s and covered by an inch-tb ick creosoted board for low tension cables and by a twoinch thick boaj.-d for high tension cables. NEW ZEALAND REGULATIONS. The New Zealand regulations state that the underground cables must be protected by armoured or suitable enclosure, though it was possible that recognition, might be given to unarmoured Trnderground cables if suitable provi' sion was made. The question did r iot seem to have been dealt with in Flew Zealand yet, in so f?.r as having t.he system allowed by regulation, although there were cases where short lengths of unarmourod cable had t> ebn used. TJSTIMATES AS TO COST.

Co? ntinuing, Mr McLeod said that he h ad made estimates or the cost of installing the different sizes and clafjses of cable. The investigations indicated that for a single phase service it was cheaper to use armoured cable than lead-covered cable, with a protecting board, but for a threephase supply the position was reversed. However, the armoured cable would be the better job, and was to be preferred. larger cables the armoured type would not appear so favourable from a cost standpoint. The calculations made also indicated •'that it would be; a wiser proposition to instal the larger-sized cables to make provision for increased load, as the additional cost was comparatively small.

In the estimates no allowance: had been made for the cost of openimg up and closing in th.e trench necesisary to hold the. cable, because that Avork could be done quilte easily by the consumer. The trench required should not be less than 12 inches —.18 inches would be better— and should i? re " ferably be cut wlciere there -was little chance of it beinig disturbed by failining operations. The Canadians us’ed a strong grading plough which turned a furrow about 18 inches deep, and the plough was drawn by a tractorWhen the cable was laid the tractor drew a scraper along to refill the’ trench. At the time of their report the Ontario Power Commission had over 150 miles of phain leatd-sheathed conductor installed underground without any protective, covering except at road crossings,, and ithe lead sheathing was used as the return or neutral conductor. It was stilted that there had been very little; tr ouble indeed. OPINION OF MR- McLEOD. Mr McLeod seated ths it his personal opinion was that if th e ground was firm and clean plain lead-covered cables would give sath ifi»ctory service provided the groi iml was not worked afterwards. In hi's opinion the use of the lead sheatl h a’e the return neutral would also ’ibe satisfactory for service with the sy stem of supply such as the board g, ave » However, both points would de ’ma nd the sanction of the Public Wort s I lepartment before the method con Id 1 i e em " ployed. The most satisfacte >ry cable,

of course, was the armoured cable, and it was also the, cheapest one that could be installed under the present regulations. A hearty vote of thanks was accorded Mr McLeod for the interesting information that ho bad given. In moving that, application be; made to the Public Works Department for permission to lay underground cables in certain suitable areas Mr Thomas said that such a system would have to be adopted sooner or later and provision would have to be made, and he foresaw a tremendous saving in the cost of poles and maintenance.