Branch and tee joints on a distribution run

One cable in, two out. What the third entry adds to the box, and what is actually published for it.

A tee is a straight joint with a leg you cannot mirror

A straight-through joint is symmetrical, and that is most of why it is easy. Two cable ends face each other. One ferrule per phase, the same tubings on both tails, then one centre outer jacketing sleeve and two adhesive-lined side sleeves closing the ends.

A branch joint gives that up. The run keeps going and a spur leaves from the same body, so there are three cable entries instead of two. The third one changes four things at once: another entry to seal, in the same hole in the ground; a core geometry that is no longer symmetrical, because the spur tails leave at an angle and no outer sleeve then recovers over an equal bundle at both ends; a second crutch, where the spur's cores fan out; and a conductor size that rarely matches the run.

That last one is where the paperwork runs out. Every ordering table in the catalogue held here indexes a kit against one cable size in one voltage class: GXS-11 for 16-50 sq mm at 12 kV, GXS-21 for 25-50 sq mm at 15-24 kV, GTJ-11 for 3x16-35 sq mm. None of them has a second column for a spur.

What the manufacturer publishes for branch work

Branch joints are named in the GTJ scope. The manufacturer's GTJ series page lists branch joints on MV distribution cable beside transition joints and PILC cable accessories up to 12 kV. Take that as scope, and it is worth having: branch work on distribution cable is inside what they make.

The figures printed under it are transition-joint figures. GTJ/1112 orders as GTJ-11 through GTJ-17, covering 3x16-35 up to 3x630 sq mm, with AC withstand 35 kV for 1 minute, DC withstand 48 kV for 30 minutes, and lightning impulse of 75 kV required against 95 kV typical. None of it was measured on a tee.

So send the two conductor sizes, both constructions, the system voltage and a sketch of the geometry, and get a kit code back in writing. A branch joint specified off a straight-through chart is a joint nobody has type-tested.

Branch off clip, GBOC 1 to GBOC 3

The one branch part in this range with a full datasheet behind it, and it is not a joint. GBOC seats in the fork where two cores split, keeps them apart and fills the void between them. Its hot melt lining is published as melting as the outer sleeve shrinks, so clip and sleeve go on in one heating operation. There is no adding it afterwards. The manufacturer lists it under telecom cable jointing. It carries no cable voltage class and puts back no insulation, no screen and no earth path.

Hot melt adhesive lining, published as melting at the same time as the outer sleeve recovers
Holds two cable cores apart where they come out of a joint
Listed by the manufacturer under telecom cable jointing, not under MV distribution
Manufacturer's page: Branch Off Clip

Sizes	GBOC 1, GBOC 2, GBOC 3
Tensile strength	2 N/mm2 (min.), ASTM D638
Ultimate elongation	700% (min.), ASTM D638
Density	0.9 g/cm3 (max.), ASTM D792
Hardness	75 +/- 5 Shore A, ASTM D2240
Dielectric strength	12 kV/mm (min.), ASTM D149
Volume resistivity	1 x 10^14 ohm (min.), ASTM D257
Dielectric constant	5 (max.), ASTM D150
Dimensional tolerance	+/- 5% on every published dimension

ASTM D638ASTM D792ASTM D2240ASTM D149ASTM D257ASTM D150

Branch off clip selection chart

Gala code	H	J	M	P	R	S	T	U	K
GBOC 1	2.5	5	12	64	28	55	13	4.5	28
GBOC 2	3.0	6	12	110	60	85	15.5	18.5	54
GBOC 3	3.0	6	13	125	85	103	17	30	79

All dimensions in mm, tolerance +/- 5%. The nine letters key to a line drawing on the sheet, which prints no legend for them and no core diameter range against any of the three sizes. Give the manufacturer the two core diameters the clip has to straddle and let them pick it.

Closing the second crutch: the three breakout families

Series	Seals the crutch of	Voltage published	Internal lining	Codes
Insulcore-LV	2, 3, 4, 5, 6 and 7-core PVC, XLPE, rubber and PILC	up to 3.3 kV	Hot melt adhesive; IP68 once installed	LV2GBB-0308 S to LV7GBB-1845
Insulcore-NT, non-tracking	3-core PVC and PILC	up to 36 kV	Water-resistant mastic	GAB-0820 to GAB-3060
Insulcore semi-conductive	3-core PILC belted, and it screens each core as well	Not published	Water-resistant red mastic; IP68	GCB-0820 to GCB-2755

A crutch seal is where branch joints are lost, because it is the one opening the run's own sleeves never reach. Codes and voltages as published. The semi-conductive family sits at 1 x 10^7 ohm.cm against 1 x 10^14 ohm.cm on the two insulating ones, both to ASTM D257 - the difference between screening a core and insulating it.

I don't have a source for that

A branch kit code. The GTJ scope names branch joints on MV distribution cable. No branch or tee ordering table is in the catalogue held here, so this page gives no kit code, no parts count and no withstand value for one. A GBOC size rule. Nine dimensions, no cable or core range, so the clip cannot be selected from published data alone. A three-way underground kit. The only three-way heat-shrink moulded part published here is GHS3-N-407, a cable harness boot with no cable voltage class. Link boxes, ring main units, separable connectors. None is in this manufacturer's published range, so no figure for any of them appears on this site. And no price, no lead time, no stock position.

When a three-way underground joint is the wrong device

People search for a three-way underground cable joint with the trench already open. The tee looks like the cheap answer because the excavator is on site today.

A buried tee is permanent. It cannot be switched, the spur cannot be isolated without taking the run down with it, and nothing about it can be tested without digging the same hole twice. Ask what happens the day the spur has to come off load. If the honest answer involves an excavator, the tee is the wrong device.

Switchgear does what a tee cannot. A ring main unit or a switching pillar takes the spur off a way, with an isolator between spur and run. Separable connectors let the spur be parted and remade in a chamber without cutting anything. A link box brings the screens out where a tester can reach them. None of those is an accessory this site indexes and no figure for any of them appears here.

The tee earns its place where the spur is fixed for the life of the asset: a lighting feed, a pump, a building supply nobody will split again. Even then you are burying three sealed entries at one location instead of two, plus a crutch, in whatever the draw pit fills with. That is the case joints that live in water is written for.

Questions this page gets

Is there a branch cable joint kit in this range?

Branch joints appear in the GTJ scope, with transition joints and PILC accessories to 12 kV. The catalogue held here prints ordering tables for straight-through and transition kits only, so there is nothing to quote a branch code from. Confirm it with the manufacturer before it reaches a schedule.

What is physically missing from a straight-through kit if you try to tee off one?

The third seal. A GXS/1236 ships one centre outer jacketing sleeve and two adhesive-lined side sleeves, which is two ends closed. A spur needs a third entry insulated, screened, bonded and sealed, and there is no third side sleeve in the box.

Is a branch off clip a branch joint?

No. GBOC holds two cores apart and its adhesive flows when the sleeve over it recovers. It restores no insulation, no screen and no continuity. On telecom cable that is the entire job. On a distribution feeder it is one small part of a job the clip is not listed for.

What seals the extra crutch on a branch?

A breakout, sized to the cable rather than to the joint. Insulcore-LV covers 2 to 7-core PVC, XLPE, rubber and PILC to 3.3 kV, IP68 once installed. Insulcore-NT is the non-tracking version for 3-core PVC and PILC to 36 kV. On PILC belted cable the semi-conductive breakout also rebuilds the per-core screen the belt never had.

Is a 3 way cable joint the same thing as a branch joint?

Same object, different vocabulary - three ways means three cable entries. Worth noticing in an enquiry, because it usually arrives assuming the part has a code and a shelf.