Cold shrink tubing: EPDM and silicone, GCTE 20/7 to 104/42

Read the fifth column, not the code

GCTE 20/7 is 20 mm as supplied and 7 mm after free recovery. Neither number is the fit. The fit is 8 to 15 mm, and it is in the fifth column.

Free recovery is what the sleeve does with nothing inside it, and on a cable it never gets there. Run the arithmetic down the chart and the bottom of every band is exactly 1 mm above that code's Df, on all seven codes. The smallest cable the manufacturer will accept is therefore one the sleeve cannot fully close onto: it is dimensioned to finish still stretched.

The upper end is looser and less regular. It sits 5 mm below Ds on the three smallest codes, 7 mm below on the next three, and 10 mm below on GCTE 104/42. Both ends of the usable band are set in from the two diameters in the part number, which is why quoting Ds and Df across a desk settles nothing.

Bands overlap, and the overlap is where the decision actually is. A 28 mm diameter sits inside GCTE 35/13, GCTE 40/16 and GCTE 53/24 at once, and neither sheet publishes a rule for choosing between them. Geometry does. The sleeve has to travel over everything between the open end and its final position, so size on the largest diameter on that path — on a terminal lug that is the lug, not the cable behind it — then check that the cable is still inside the same band.

Choosing the compound, and where the range stops

Nothing dimensional separates the two, so the compound is decided on the table above and on what each source is prepared to claim. EPDM holds the tougher record: 750% elongation, 1.8% weight gain after seven days at 90 °C in water, and — on the manufacturer's EPDM product page rather than on its datasheet — ozone resistance, wet electrical performance and a statement that the compound withstands backfilling. That last line is the buried-joint argument, and no silicone source makes it.

Silicone answers with the higher dielectric strength, 18.0 kV/mm minimum against 14.3, and it is the only one of the two whose sheet prints a hardness, 40 ± 10 Shore A, alongside a volume resistivity of 1 × 10¹² Ohm.cm minimum. Its elongation is published as 400% minimum where EPDM's is 750%. The wider argument between elastomers and polyolefin is at shrink tube materials.

Both sources state that the compound carries neither chloride nor sulfur, and neither says why that is worth printing. It is a compatibility statement about what the sleeve sits against: chloride is the classic initiator of stress-corrosion cracking in austenitic stainless steel, and sulfur tarnishes silver and copper contacts. Read the ANSI C119.1 line just as narrowly — both sheets claim the water seal requirements of that standard, not the standard entire, and neither cites a clause.

1.1 kV is a hard ceiling. This range seals inline connections and terminal lugs on copper and aluminium to 1000 sq mm, and the census of what else the cold shrink range does and does not contain is at cold shrink. Past the ceiling the part changes with the mechanism: medium and heavy wall tube carries insulating duty to 36 kV, and the torch-against-pull-cord trade is settled at heat shrink or cold shrink.

Two adjacent cold shrink parts are deliberately outside this page. The GCCE close-ended cap seals a cut end rather than a connection, and it is indexed at anodecap.com, a reference the publisher of this site also runs on the same manufacturer's range. The GCEB crutch sleeve for two- and four-core cable is held on cablebreakoutboots.com, the same publisher again. Dimensions for both are on the cold shrink size chart and nowhere else here.