Buried, wet and carrying current: the anode lead wire

Three duties at one millimetre of the assembly

Place the joint before you place the part. An anode is set in backfill picked for its conductivity — the wettest, most electrolytically active ground anyone on the project chose on purpose. The lead wire leaves the anode body inside that backfill. Nothing here cycles wet and dry the way a splash-zone part does: the joint is buried, and stays buried for the design life of the bed.

The cap does three separate things across a few millimetres. It relieves mechanical stress where the wire emerges, so settlement load and installation pull are carried by the moulded shoulder instead of by the connection. It excludes moisture from that connection — a seal, not a cover, and the mastic is the whole difference between those two words. And it insulates the exit, because the entire output of the anode passes through this one joint on its way to the ground.

The body is a highly cross-linked polyolefin. Inside it sits a rubber-based mastic that softens under heat and keys to two dissimilar surfaces at once: anode material at the wide end, wire insulation at the narrow one. That bond is what the IP68 figure describes; the polymer alone would not earn it. Shrink a lined cap over contaminated insulation and what you have installed is a cover with water trapped beneath it — worse than an open joint, not safer.

Two diameters and three lengths describe every code, in the notation used on every chart across this site. D is the anode-end internal diameter, d the wire-end internal diameter. Subscript s is the part as supplied; f is after free recovery, shrunk with nothing inside it. Ta and Tw are the recovered wall thicknesses at each end. The supplied bore has to clear your anode; the free-recovery bore has to finish below it, or the cap never grips. The size chart page sets GAC beside the site's other three charts.

What the GAC cap will not do

Limits worth reading before a specification is written around it.

• It does not extend anode life. The anode consumes at whatever rate current density and backfill resistivity set; sealing the wire exit changes neither.
• It does not replace a survey. A bed with every joint capped correctly still has to have its potentials read on schedule.
• It carries no system voltage class. The 12 kV/mm figure measures the wall material; nothing published assigns this part to a circuit rating.
• It cannot be refitted. Once recovered, removal means cutting the cap away and fitting a new one, so a trial fit is a wasted cap.
• It cannot be applied cold. Recovery starts at 125 °C, so a torch or hot-air gun is required; where a permit forbids one, see closing an end where a torch is not allowed.
• It is not a pipeline or pre-insulated pipe end closure. Those sit outside this site's scope and are listed as such on the FAQ.