CA2008229A1 - Moisture-impermeable stranded electric conductor - Google Patents

Abstract

ABSTRACT

In a method of manufacturing a moisture-impermeable multi-wire electric conductor in a single operation, a metal core travels continuously in the direction of its length and a viscous semi-conductive moisture-impermeable compound is applied to the advancing core to form around the core a coating of the compound of a predetermined uniform overall diameter. Wires are helically applied to the advancing coated core to form a layer of helically extending wires around the core. The radial thickness and overall diameter of the coating of moisture-impermeable compound having regard to the number and cross-sectional areas of the interstices bounded by the advancing core and the wires are such that each of the interstices is filled with moisture-impermeable compound throughout the length of the conductor. The core may be a single wire or a plurality or wires stranded together.

Description

0,1/l9~ 30 1`1~, 5g3 P0E~q 2~ 29 ~ . .

Thia 1 nventlon r~lat~ to ~lectrlc c~bles o~ the klnd havin~ on~3 or tnore than on~ ela~trlc cond~ct~r comprlsln~ ~ plurality o~ wlre~l or oth~r rl~xi41e elongate el~ment~ o:e metal or me~1 alloy ~tr~nded or 5 otherwi~e a~em~l~d to~eth~, the or ~Ch condllctor ~elng surrounded by ~t l~n~t o~ ~xt:rud~d l~yer o~
pla~lc~ m~te~i~l. For convenler~ca, All ~uch ~l~xib~o element~ o~ m~tal or metal alloy her~ain~fter wlll be include~ 1~ th~ ~nerl~: term "wi~8 " . T~ pl~tlcs 10 mat~3rlal of t}~e ~xtruded l~er lmrn~dl~t~ly Ad~cent the oute~l~09t l~yer o~ s~lre~ he or ~ach condu~or sub~tant~ally flll~ int~r~ic2~ b~tw~n th~ WirQ8 o~ th~
outermo~t l~yer o~ wir~s and 1~ u~u~lly, but no~
~IBC13E~3~ri:~y, s~am~ -~o~ductl~re l~e~elu0~ it ~ 9 tha nor~nal 15 practlce ~or th~ ~x~ru~ y~r o~ plA~Eltlc2 materl~l ~mnedlately ad~ ac:ent the conduc~or to co~tltu ~ a conductor ~cr~nO
W~ th D. vie~ to subo~ lally rec~ucln~ ri~k o~
moi~tur~ p~ne~ration ~lorlg ~ nt~r~ce~ wl~hl~ a ~0 corlductor conal~ting o~ Q ~lur~ o~ wiro~ ~krando~ or oth~wise a~embl~d tosetA~r, lt ~8 common practlce . or ~he l~ters~l~e~ wnolly bounfl~ by th~ wlrss o~ the conduc~or t~ be ~stan~i~lly ~ille~ w~ a . eml-conc~uctlv~ moi~tu~e~ m~ ompound throu~hou~c ~5 ub~antially tha wh4ie len~th o~ the co~duc~or.

~.. . , -: , :

~ `. ,,', , ~

0.~/19/~ 30 NO. 593 P005 2~2~9 an ob~ Qct o~ tho pre~nt lnv~ntlon to provlde an im~rov~d method o~ m~r~u~cturin9 a sub~t~ntlally moi~turl3-lm~e~me~ multl-wire el~ctric conduc~or by me~n~ o~ which ~ho ~onductor c~n be 5 marlu . ~ctured an~ ren~r~d ~ub3tantl~11Y
mol~ture-imp~rme~ble ln ~ 815~10 o~r~t~ OJl.
Accordlnç;~ to the lnv~is3n, t~e l~nProv~d~ m~th~d comprl~ aU~ing a ~lexl~le ~310nç~atla Core o~ m~tal or metal alloy to tr~vel eon~inuou~ly ln th~ dlr~ction o~
10 1t:8 len~th: applylng viscou~ o~ condu~tive molstur~-lm}; ~rmeable compound to th~ advatlcln~ co~e to form around th~ core ~ lon~itud~ n~lly and clrcumferentially contlnuou~ c~ in~ o~ th~ compound o~ .
a predet~nin~d 8ub~tantiMlly unl~orm o~orall dlametsr ::
lS throu~hollt the length o~ the cor~3; and h011aally applyi~l~ a ~lur~lity Or wir08 ~o th~ ~vancin~ co~ted core to form a 1 yer of hqllcall~ ~x~ndin~ wlrq~s around ~he core, the radlal ~chlckne3s 2md overall ~ e~er o~
the coatlny of vlscou~ ~enll ~Qnductive ~0 molstur~-imp~rmeabl~ ~ompo~md h2~nsJ r~ard ~o th~
nu~T~er and cro~ ectlonel7 BX~L61 o~ the lnt~rstlc0~
bounded by the advancln~ cora ~n~ wi~o~ o~ lay~r beln~ such ~hat ~ach o~ said lnte~lce~ is ntially rilled wi~h vi~cou~ ~sani-con~uctlvQ
25 mo~ stu~e-imp~ ble com~ound~ throu~hout the l~n0~h o~
'c~e conducl:or.

. . . . .
. , - : .
.
' '''' ', '' .' ' ' . ;
:; .'- ' ~ . , : :

0~/i9~80 ' lii:30 NO. 593 P006 2~ 29 3.
Preferably, th~ coat~ o~ vi~cou~ ~emi-~onduct~ve moi6ture-im~ermoa~le compound c)~ pr~d~ta~nllnad ~ub~tan~lally uni~orm ovor~ll di~ ormed around kA~ adv~nclng core by c~u~n~ l~h~ core to tr~ve~l ~nto 5 ~hamber ~ tan'cial~Y ~ wl~ch vi~cou4 ~eml-conductlve snol~tur0-lm~erm~ com~olm~ m~ln~alnad at ~ ~ubs~antlally aon~tant F~ros~u~e ~nd tem~er~'cur~ ~nd out o~ th~ cham~ through ~ ord~r to m~intai~
the viscou~ condu~tiYe 3nol~ure-lm;p~rm~
lO co~npound ln th2 ch~mber a ~ 0u~0t~ntl~l ly c~n~tarl~c pre~sur~, the volum~ of th~ ch~ r i~ automatic~lly $~r~dual~r r~duce~ a~ the quantl~y Or compoun~ in th~
~hamber :~a~ l~; when th~ volum~ o:e th~ ~hamber ha~ been re~uc~d to ~ ~regetermlne~ valu~, vi~cow 15 ~emi-conduc~lve mol~tur~ lmperme~lo com~ound i~
automatic~lly irl~croduc~d lnto the ch~er and th~ volum0 o~ t~e ~ham~r i~ au~omatlcally ~ra~lu~lly lalcre~od o accommodat~ ~h~ additlo~al compouxld; and. when the ~falue of th~ ~hamber h~ b~n lncre ~ed to ~
ao p~edet~ ned tr~lu~, in~odu~tlon n~ ~dCiltional ~om~ound lnto ~che ~h~n~e!r ~s autom~tically ~to~ed and thl~
~ecIuerlce Or au~atl~ oPera~ion~ 1~ xepeated aa r~qulred .
The ~:ha~tr whlch 1~ ta~t~ally rllled wi~h 25 viscous se!mi-coF~ductlv~ mol~cure-impe~m~bl~ ~om~ound . .
- , . . - ~ -~ ' ' ' '' '' . ~ , ' : ~ . . . ~ . , -. . . ~: :
... .
.. ... .

: , ~)1/1' 16:30 NO. 593 P007 2~
-~nd who~ volumo 1~ autom~tica;lly ~r~uallY d~cr~a~-d or ~ncroa~d ~ requlrad pro~r~b.ly 1~ con~ltut~d by th~
bore o~ ~ cylind~r in whlch works a pneum~tlcally or hydraulic~lly o~r~ed ~lstun, o~or tlon Or the ~ ton 5 beln~ controll~d by m~no whlch automatlc~llY ~n~e~ t~o ~?o~itlo~ ~ th~ ~$~ton wi~hln t;b~ c:ylin~er, a~d h~nc~
~utom~tic~ sanaes the volum~ o~ the cham~er, ~nfl which also au~omatlcallY ~ctivat~ ~d d~ tiv2tes a pum~ ~or intro~ucin~ vi~cou~ c~n~uc1:ive 10 w~t~r-lmp~rmeable ~om~ound in~o ~he chamber.
Th4 ~eml-cor~ductiv0 mol~u~a impe~m~abl~3 compou~d periodically i~troduc~d ln~ ~h~ ch~mber 1B suxsplled~
rrom a ~ou~e at which 1- i~ mai~talne~ At a ~emp~ture ~u~ icient to ensure that the co~n~ound i~ o~ the desired 15 viac:osity~ The ~om~ourad withln ~he chaml~er ~chrough wht~h ~he ~lexlble co~0 continuou~ly ~crav~
maintained at ~ bst~nti~lly ~on~t4nt ~em~ra'cur~
~u~ficient eo ~r~sur~ th~ he co~ou~ of th~ de81~d ~-viscosity by mean6 o~ hea~ln~ m~n~ which i0 ~ c12t~d ~0 w~ th the chan~4er ~nd whl~h can bo ~ltomatlc~llY
con~roll~d ~o malntaln 'che ~ompound in th~ chan~ber at th~ desir~d ~ t~ntl~llY ~on~ant tem~er~tur6~.
Th~ ~ie thrsuçrh whlch 'che ~dvanclng core em~r~
from ~he chamb~r ~r~r~bly i~ con~itutod by a c~rbid~
25 wirs drawln~ ~le.

: - ' - .

0~ 9 i~: 31 NO. 593 P00~3 ~ re khe ~on~uctor 1~ r~nded cenductox con~l~tln~ o~ seven wire~, th~ x.~bl~ cor~ w~ e constitu~ad by a ~in~le wir~3 a:rouz~d ~rhlch th~ ~ix oth~r wir~8 o~ ~he c~onduc~-or wlll ~e h~lla~lly ap~ d ~ r S the longltudi~ally atl~ clrawn~larhntl~lly c~ntinuou~
coatln~ o~ vi~cou~ ~eml-condu~tl~0 mol~tllra-imF~erm~le compound h~ b~on ~p~lied ~o th~ aingle wlre.
whRre~ the conduGtor i~ ~ ~t~ d condu ::tor con~lstin~ af nlneteeII wlr~ o~ the ~r~t6~r~tic~
10 within and wholly ~c)unded by wlroa of th~ ~tranded ~ondu~o~ x~refar~blY 14 ol~eated ~ n Swo operatlon~
carried out ln tand~m, ln ~h~ t o~ whlch a strand~d c:onductor o~ sev~n wi~e~ wlth th~ ln~er~ wl~hin ~he conductor sub~t~n~i~lly ~illed With vl~cou~
5 seml ~onductl~e mol~tur4-im~ ompounCI i.5 ~ormed a~ here~ fore descrlbed ~n~, in the ~cond o~ whlch, the ~lexlbl~ ~ore wlll be co~stitu~d by tho ~tr~ds~
conductor o~ ~even wire~ arou~d wh~ch th~ twaLv~ oth~
wire~ o~ th~ conductor will b~ h~ ally ~p~lled aftor 20 the lorlgitudlnally ~nd ~ircum~0n~1~11y aontlnu~u~
coatlng o vl~ous seml-cond.uctiv~ moi~ture-lmpormeable ~omp~und ha~ b~e~ a~lie~ to th~ ~even-wl~ con~a~r.
Expr~s~ln~ th~ ~ra~r~od m~thod do~lb~d lh the p~ec~dln~ ~ar~raPh i~ mor~ ~n~r~l ~orms, wher~ a ~5 ~tranded condu~tor cons~ Or ~ mul~i~lici~Y of wlres 1~ n lay~x~, ~h~ wlr~ o~ ~h~ ~n~xmost lay~r b~in~

- , . . .. . . . .
, . . .. . , ... - .~ . i , .

:~ , .. .:
: , ,, ,. . - : , ~ . :.
~: :.:. -.

2~ 9 0~/19/g~ 16: 31 I~o. 593 P009 hellc~lly a~pll~3d a~ound o~ ~lns~l~ wi~e ~ tho wir~t~ o~
each 3uc~eedlno l~y~r baing h~llcellly ~plled ~round the ~rece~in~ layer, f llllnç~ o~ th~ lnt~r~ti~o5 withlr~ and wholly bc)undl3d by wi~e~ o~ th~ ~rand~d conductor 5 pr~r bly 1~ ef ~ected lr~ 11 opera~io~s c~rrl~d out in tan~lem, The lnverl~i4n al~o lnclud~3~ ap~aratu~ ;eor uae ln :
tlle manufac~cure o~ a ~ tantl~lly moi~tu~e-lm~erme~le multi-wir~ el~ctrlc condu ::tor ~ hor~lnb~ore ~0 d~cril;~ed.
The ln~en~lon ~urth~ clu~las a mol~cu~e~ able mul~i-wi~ olactrl~ conduc~or manufactu~ed b~ ~he lmproved me~'chod h~re~ fo~
deBCribed .
l~ inventlon i~ i~u~t~l9r lllustr~t~d ~y a ~le~riptlo~ by way of ~xun~le, o~ the pxe~3rred m~tho~
o~ m~nu~c~urin~ ~ subs~ tially moi~tur~-lmx~rm~
multl-wlr~ ctr~c co~ductor ~omprl81ns~ ~ ~ln51~0 c~3n~ral wlre ~n~ ~lx wtr~s hollc~lly a~?l?lie~ around th~
20 cantral wire wlth re~erænc~ to th~ accom~anyln~
dl~sJralJnmat1c ~r~wln~ which ~how~ A Islde v~w, p~rtl~r in s~ction a;nd partly in ele~ratlon, o~ pre3~red a~ratu~
~or ~pplyinç~ ~ longitudlnallr ~n~ ~lrcum~ero~tially continuou~ coatl~g o~ vls~ous ~?ml-~onduc!tlve 25 moi~tur~ imp~rmeable c:om~ound to ~h~ central wir~.

. . . : .. ~ . . . :
, . :.. . ... .
- . : . - . .
. . :. ,, . . ... .
- . . . ~

.
.
.

01~19~ 16:31 NO. 593 P010 20~BX~9 R~errlng to th~ dr~win~, ~ho ~r~ r~d ~par~u~
~or applyin~ ~ lon~ltudln~lly ~nd clxcum~re~tl~lly c~ntlnuou~ coatin~ o~ vl~cous ~ml-co~duc~lv~
mols~ure-impermeable compoun~ to th~ c~ntr~l wlx~ o~ ~h~
multl wlre conductor comprl~ cyllnd~r 1 havin~ a ~or~ which work~ ~ p~m~ ally ~p~r~t~d ~l~ton 3 h~vi~g ~n aBBOCla~Qd pn~umatlc compr~ion cyllnd~r 4, The ~ore 2 ~ th~ cylln~er 1 c4~ti~ute~ ~ ch~mb~ to b~
fllled wlth vlscou~ a0ml-conductiv~ moi~ure-imp~rm~ab12 compound Which wlll be m~int~lnod ~t ~ con~t~nt prea~ur~
and ~emp~rature and throu~h which th~ c~ntr~l wir~ ~not ~hown) o~ the mul~i-wir~ conductor wlll b~ cau~d ~o travel vla a~ lnlet 5 a~d ~n ou~t 6. A carbide wlro dr~w1ns;J dia 7 1~ posed lmme~l~tely adi cent the outlet 6. the ls~ternal ~l~m0tor o~ ~he dl~ beln~ BUCh th~t the coatials~ o~ vl~cou~ condus:kiv~s moi6~ure-im~ermeabl~ compo~nd on ~h~ c~nt~al wixe eh argln~ ~ th~ ch~ 2 will b~ o~ ~h~ de~lred :
overall d~net~3r and h~nce ~dial th1ckne~.
Op~ration of tho ~l~to~ con~rollea by ~
sen~o~ 8 w~lch automa~lcally ~e~e~ ~h~ po~l~ion o~ the pi~ton within the ~ylind~ 1, a~ hen~e ~tom~tlc~lly ~ens0~ th~ v~l~me o~ ~h~ ~h~mbo~ ~, and whlch ~utom~tlcally actlvat~ and d~-~çtiv~t~ a pwnP ~not shown7 ~or lntrvducin~ throu~h An ~ 3t port ~ into the chamber vl~ous ~emi-~ondu~tive w~t~r~ rme~
compou~d ~rom a source ~not ~ho~m3 a~ which lt 1 , .- . ... , . ~ , ,. . : ;
.~ -- . . . ,. , - :
:: - .. . . ~ .

:. . , ., : ~ :
- , , .. . .
,. .

01/19~ 31 r~o. 593 P011 20~ g malntalr~d ~t ~ t~m~w~ture~ ~u;~tciant to ~nl3ure~ that th~3 compound i8 O:~ the de~lred v~co~lty- Com~ound withln t~e eh~ r 2 oan be contlnuou~l~r m~ln~in~d ~t conH~ca~t ~em~er~ture ~uX~lcio~t to on~ure that lt 1~ of S the de~i~e~ v18co~1~cy S~Y m~n~ o~ an ele~trlc h~at~r 10.
Exce~ viscou~ ~@ml-conductlve moi~tur~-:lm~ermeable compound lowinlJ . rom t~ ~Ir~win~ di~ 7 ~an b~ co~l~cted in a rQs~rvoir tnot ~hown) po~ltlon~d b~n~a~h th~ die, where th~ exca~ com~o~nd can be pum~ed bae3c lnto the 10 sourc~ o~ com~ourld.
In u~e, th~ centr~l wirs o~ th~ multi-wire conductor to be fo~ne~ 1~ c~U~e~ to tr~v~ the dlrectlon of ~ta len~th throu~h ~he cham~er 2 vla the inlet 5 ~nd outlet 6. th~ ch~ 3r belns~ d with ~S vi~ou~ semi-corlductive mol~turs~ 3rmaa~ ompound 80 that, on emer~ln~ f r~m tha drawlnSJ diQ 7, the wlre h2~ a longltudin~ and circum:Eor~n~lally co~t:l nuou~ coatln~
o~ t~se compou~d o~ a ~rqde~ermir~ nlYorm osr~rall dlame~er, an~ hen~e radial 'chic~ , throu~hou~ ~he 20 len~th o~ ~he wire. A~ th~ quantity of compound 1~ the chamJ~er 2 ~alls ehe xSl~ton 3 coD,~c~nuou~lY worklnçr in the~
cyllnder 1 automatlcallY ~r~Clua~ ly roduco~ th~ volum~ of the cham~r ~o that ths ~ ur~ o~ th~ V~ OUB
seml-con~uctiv~ moi~tur~-lmpe~ om~pound i~ th~
25 chamber i~ maintalnod conlatan ~ Wh~n th~ ~olume o~ th~
chamber 2 has b~3n red~lc~d ~o a pr~d0~rmln~sd valu~, th~a :
po6ition o~ ~he pl~o~ 3 lo ~ d by tho 8~3n80r 8 whi~h .. . . .. . . .
.. .

.-:. ~ - . .. .

01/19/9~1' 16: 31 NO. 593 P012 %9 9.
automatic~lly ~c~iv~te~ ~ ~Ump 'co lnk~oduci~s ViElCOUJ
~eml-con~uc~lve mol~ture-imp~rm~ om~ound vla the inl~t port 9 into the cham~r .~ ~rom th~ ~ourc6~ o~
com~ourld ~not ahowni. Wh~n t~3 volume o~ the chamb~r, S whlch is now automatic~lly yr~ually incr~aain~ to acconunod~t.e th~ addl.tlon~ 4m~0url~, h~ln bb~n lncroase~
to a pr~dat~rmin~d v~lua, th~ ~ltlon o~ ~ho ~l~ton 3 i~ ~ens~d by th~ ~an~or 8 Which ~utomatl~2lly d~-activatq~ hC p~ o ~t~ lntro~luctiot~ o~ fu~ther 10 compound lnto the cham~er. Th~ ~e~U~nC:e o~ au'come~Slc o~eration i~ r~3~aate~ a~ r~ u~ln~ m~nu~z~turl3 o~
the mul~l-wlre cs: n~ucto~ .
Down~3~ream Df ths dr~win~ 7, the centr~l wir~
wlth th~ coa~ln~J o~ ~om~pour~ e~oon ~aa~
15 standard w~ro ~r~ndin~ m~chln~3 whor~ ~ix wire8 ar~
helically ap~ d to th~ adv~ncil~g coa~od wlro ~o ~orm a lay~r oi~ h~ ally ~x~sndirlg wl~ ou~CI th~ c~s~tr~l wir~. The ~adi~l thlck~o~o ~d ov~r~ll diamet~r o~ h~
c:oa~ing o~ compound on th~ c~nt~l wlr~ h~vinQ :~sJ~rd t~
ao th~ numbQ~ and ~ro~s-a~ctlonal a2:eas o~ th~ in~r~tic~
bounde~ by th~ advancl~ xal wlr3 ~nd th~ ~lst wlre~
o~ the l~y~r ~ uch th~ oach o~ the~e interstic~
fiLlQd with vi~ou~ ~emi-co~uc~lvo moioture-lm~srm6-Ablo compound throu~hout ~he l~n~h o~ th~ c~nduc~o~.
Th~ im~rov2~ m~thod o~ m~u~acturl~ a ~ubstantially m~is~u~ multl-wlre ~l~c~c~ic .. , ~ ... . . ..
..
~, ~ ,, , , ; .
:
. .
' 0~/19/9~3 i6: 31 NO. 593 P013 2(~t_~9 .
10. ~ .
conductor ha~ the lmportont ~vant~o tnat th~ c~ ductor c~n be mAnufactur~d ln ~ ~lin~lo o~o~tl4n i~r~ ctlv~
o~ tha number o~ wlre~ o~ wh I ch ~h~ con~luctor i~ built u~ he imz: rov~d appnr~tu~ ~ol^ Ua~ in the manui~ctu~e 5 of ~ su~s~antl~lly mo~4~ure~ bl~ mul~l-wl~0 ~loct~ic conductor ha~ th~ importan~ advanta~7e th~t it i~ aimple and lnexpenl31v~ Pnd can ~ r~a~ilY u4ed ln tarldam wl~h a 8~ nd~Yd wire ~trat~dln~ m~chlne.

Claims (11)

1. A method of manufacturing a substantially moisture-impermeable multi-wire electric conductor, which method comprises causing a flexible elongate core of metal or metal alloy to travel continuously in the direction of its length; applying viscous semi-conductive moisture-impermeable compound to the advancing core to form around the core a longitudinally and circumferentially continuous coating of the compound of a predetermined substantially uniform overall diameter throughout the length of the core; and helically applying a plurality of wires to the advancing coated core to form a layer of helically extending wires around the core, the radial thickness and overall diameter of the coating of viscous semi-conductive moisture-impermeable compound having regard to the number and cross-sectional areas of the interstices bounded by the advancing core and wires of said layer being such that each of said interstices is substantially filled with viscous semi-conductive moisture-impermeable compound throughout the length of the conductor.

2. A method as claimed in Claim 1, wherein the coating of viscous semi-conductive moisture-impermeable compound of predetermined substantially uniform overall 12.

diameter is formed around the advancing core by causing the core to travel into a chamber substantially filled with viscous semi-conductive moisture-impermeable compound maintained at a substantially constant pressure and temperature and out of the chamber through a die.

3. A method as claimed in Claim 2, wherein the volume of the chamber is automatically gradually reduced as the quantity of compound in the chamber falls; when the volume of the chamber has been reduced to a predetermined value, viscous semi-conductive moisture-impermeable compound is automatically introduced into the chamber and the volume of the chamber is automatically gradually increased to accommodate the additional compound; and, when the volume of the chamber has been increased to a predetermined value, introduction of additional compound into the chamber is automatically stopped and this sequence of automatic operation is repeated as required.

4. A method as claimed in Claim 3, wherein the chamber is constituted by the bore of a cylinder in which works a piston, operation of the piston being controlled by means which automatically senses the position of the piston within the cylinder, and hence automatically senses the volume of the chamber, and which also automatically activates and de-activates a pump for introducing viscous semi-conductive water-impermeable compound into the chamber.

13.

5. A method as claimed in Claim 2, wherein the semi-conductive moisture-impermeable compound periodically introduced into the chamber is supplied from a source at which it is maintained at a temperature sufficient to ensure that the compound is of the desired viscosity.

6. A method as claimed in Claim 5, wherein the compound within the chamber is maintained at at substantially constant temperature sufficient to ensure that the compound is of the desired viscosity by means of heating means which is associated with the chamber and which can be automatically controlled to maintain the compound in the chamber at the desired substantially constant temperature.

7. A method as claimed in Claim 1, 2 or 3, wherein the die through which the advancing core emerges from the chamber is constituted by a carbide wire drawing die.

8. A method as claimed in Claim 1, 2 or 3, wherein the flexible core is constituted by a single wire and six wires are helically applied to the advancing wire to form a stranded conductor consisting of seven wires.

9. A method as claimed in Claim 1, 2 or 3 in which the multi-wire electric conductor is a stranded conductor consisting of a multiplicity of wires in n layers, the wires of the innermost layer being helically applied around a single wire and the wires of each 14.

succeeding layer being helically applied around the preceding layer, wherein filling of the interstices within and wholly bounded by wires of the stranded conductor is effected in n operation carried out in tandem.

10. A moisture-impermeable multi-wire electric conductor manufactured by the method claimed in Claim 1, 2 or 3.

11. Plant for use in the manufacture of a substantially moisture-impermeable multi-wire electric conductor comprising, in combination, apparatus for applying to a flexible elongate core of metal or metal alloy travelling continuously in the direction of its length a longitudinally and circumferentially continuous coating of a viscous semi-conductive moisture-impermeable compound and, downstream of said coating apparatus, a machine for helically applying to the continuously coated core a plurality of wires to form around the core a layer of helically extending wires in which the interstices bounded by the advancing core and wires are substantially filled with viscous semi-conductive moisture-impermeable compound throughout the length of the conductor, which coating apparatus comprises a cylinder having a bore which constitutes a chamber to be substantially filled with viscous semi-conductive moisture-impermeable compound through a filling port in the chamber and which has axially 15.

aligned inlet and outlet ports for passage of said core therethrough; a die downstream of said outlet port for determining the overall diameter of the coating of viscous semi-conductive moisture-impermeable compound on the core; a piston working in the cylinder; a source of viscous, semi-conductive moisture-impermeable compound;
a pump for introducing through said filling port into the chamber viscous semi-conductive water-impermeable compound from said source of said compound; and means for automatically sensing the position of the piston within the cylinder, and hence for automatically sensing the volume of the chamber, which sensing means, when the volume of the chamber has been reduced to a predetermined value, automatically stops the piston and activates said pump and, when the volume of the chamber has been increased to a predetermined value, automatically de-activates said pump and restarts operation of the piston.