Multiconductor power cable from 600 V to 35 kV

One family with several constructions

At 600 V a power cable is a jacketed assembly of two to four conductors with a ground, insulated in XHHW-2, RHW-2 or THHN and suitable for tray, conduit or direct burial depending on the listing. Above 2 kV the same cable gains a semiconductive conductor screen, insulation thick enough to be measured rather than described, and a metallic shield over it.

Above 5 kV the shield becomes a copper tape or a set of concentric wires with a drain, and the jacket becomes an oversheath whose job is to keep water out of the shield. Three-core assemblies in the middle ranges are common in plant distribution; single-core cables are common where pulling tension or termination space rules them out.

Reading the sizing line

A typical print reads as a compressed sentence: three single conductors, 500 kcmil, 15 kV, 133 percent insulation level, EPR insulation, copper tape shield, PVC jacket. Each element changes who can use the cable. The insulation level is the one most often missed: 100 percent cable is thinner-walled and intended for a solidly grounded system, while 133 percent suits systems where a ground fault may persist.

Conductor size appears in AWG up to 4/0 and in kcmil above it, and the two are not interchangeable in conversation. A reel labelled 4/0 is not the same as 250 kcmil even though they are close in ampacity, and a set that mixes them cannot be paralleled.

Armored and unarmored

Interlocked aluminum armor over a cable assembly gives mechanical protection without conduit and is common in plant retrofits where the route is exposed. The armor is not a ground path on its own; the assembly carries a bonding conductor and the armor is bonded at terminations. Corrugated and continuously welded armor variants turn up where the cable runs outdoors or in wet process areas.

Unarmored cable relies on its jacket and, indoors, on conduit or tray. That makes the jacket the condition question. A power cable that has been pulled through a badly swept conduit arrives with a jacket scuffed to the shield, and that is visible without any test equipment.

• Voltage class and insulation level on the print
• Shield type: tape, wire, or none
• Jacket continuous, no scuffs through to shield
• Ends sealed against moisture
• Single-core or three-core stated plainly

What decides a power cable review

Three things, in order: what the cable is, how much of it there is, and what has happened to it since it was made. The first is print, the second is measurement, and the third is a walk along the reel looking for flattening, water staining and jacket damage.

Plant distribution work in Ohio generates this cable continuously. A mill that replaces a 5 kV feeder, a hospital that adds a normal and emergency pair, a water plant that reworks a pump station: each leaves a mix of full reels, part reels and pulled lengths. The pulled lengths are the ones that need the closest look, because a cable that has been in service has been heated, and heat leaves the insulation visibly stiffer at the ends.