GTJ transition joint: PILC to XLPE

The job that puts a GTJ on the requisition

Nobody picks this kit off a blank sheet. It arrives because there is already paper cable in the ground. An old paper-insulated lead-covered feeder gets extended to a new substation, diverted round a road widening, or repaired after a dig-in — and the length going back in is XLPE. Where the two runs meet, two constructions have to be reconciled inside one splice.

Make off the paper side and you have oil-impregnated paper, a lead sheath and steel armour under jute. Make off the XLPE side and you have extruded insulation, a semi-conducting screen, a copper screen and a PVC oversheath. The earth reference is established differently at each end, and the paper side goes on pushing oil towards the new cable for as long as the joint stands.

So a GTJ is not a straight joint with an extra sleeve dropped in — its bill of material is drawn against two cables at once. GTJ/1112 covers systems to 12 kV; GTJ/2436 carries the 24 kV and 36 kV classes in one series. Both are published for three-core cable on both sides. If either end is single core, no GTJ code applies: that is GXSS/1236, one construction on both sides. Two ends of the same paper cable are a GPS joint, never a GTJ.

Read the two cable lists before you read the kit list

The 12 kV drawing gives the XLPE side a semi-con layer and stops. The 24 and 36 kV drawing names a semi-conducting screen and a copper screen as separate items — a second earth path arriving at the joint, which is why the higher-class kit reworks its stress-control items rather than adding more of them. The paper side moves too: belting is named as the inner sheath at 12 kV and is gone above it, replaced by a paper inner sheath and a twelfth callout for the paper outer sheath. Check the old cable against the drawing for your class before a code goes on a schedule.

Two items are the transition, and three lines move underneath them

Item 1 and item 3 are the transition itself. A barrier-type inline connector at the ferrule position, three per kit, and a heat-shrink oil barrier sleeve, also three per kit, on both series. Of every joint sheet in this range only the two GTJ lists name a barrier connector — GXLT, GXS, GXSS and GPS all take a plain crimping ferrule. Oil out of the paper has nowhere useful to go inside extruded insulation, and those two items are what stop it getting there.

Item 4 is where the two kits part company outright: three lengths of conducting tubing at 12 kV, one length of semi-conducting tubing at 24 and 36 kV. Item 18 moves the other way — six jubilee clamps against two. Count against the sheet for your class, never against the three letters on the label.

Item 9 is the line to query before it reaches a tender; the counting is set out on the kit contents page, and the tubings themselves on the sleeves page. Where each one lands in the build order is the installation sequence — every sleeve goes on before the crimp, and on this joint that means threading them past two different oversheaths.