belted cable

A belted cable is a three-phase power cable where the three current-carrying conductors are grouped tightly together and wrapped in layers of oil-impregnated insulating paper, then sheathed in lead or aluminum. The "belt" is the paper wrapping itself, which provides both electrical insulation and mechanical protection. This construction was standard for industrial power distribution from the mid-20th century through the 1980s, particularly for cables rated 5 kV to 35 kV.

The three conductors sit in a triangular or flat arrangement at the cable's core. Around them winds the oil-saturated paper belt, typically 0.5 to 2 mm thick depending on voltage rating. This paper acts as the primary insulating medium, with the oil keeping it flexible and improving dielectric strength. An outer metallic sheath (usually lead) contains everything and provides mechanical and environmental protection. The entire assembly is then protected by an outer jacket of PVC or similar material.

Belted construction differs fundamentally from screened (or shielded) cable, where each conductor has its own individual paper wrapping and the group sits inside a copper tape screen. Belted cables cost less to manufacture and were simpler to install, but they cannot be run in parallel with themselves or other cables as easily, since the lack of individual shielding makes them sensitive to inductive coupling and cross-talk over long runs. They also degrade more rapidly if moisture penetrates the outer jacket.

Decline and modern practice

Belted cables are rarely specified for new installations in North America or Europe today. XLPE (cross-linked polyethylene) insulation, introduced in the 1960s and perfected through the 1980s, offers superior moisture resistance, higher operating temperatures, and simpler termination. Most utilities and industrial users have phased out belted cable in favor of single-core XLPE or EPR cables. However, many belted cables installed decades ago remain in service, and technicians still encounter them during maintenance, refurbishment, and troubleshooting of older facilities.

The name "belted" describes the characteristic wrapping technique: the insulating paper is literally belted or wound around the bundled conductors. The oil saturation was essential because dry paper would crack under thermal cycling and vibration. This terminology persists in utility and electrical engineering circles, even though the technology itself is approaching obsolescence in the developed world. Proper identification of belted cable in the field matters because its termination, testing, and thermal characteristics differ significantly from modern cable designs.