It's Almost Never the Cable: Why Terminations Are the #1 Failure Point in MV Systems

When a medium-voltage cable run fails, the instinct is to blame the cable. But the cable itself—a solid, factory-built, quality-controlled product—is rarely the culprit. The failure almost always happens at the ends: the terminations and splices made by hand, in the field, often in less-than-ideal conditions.

Industry data backs this up. Studies attribute roughly 43% of medium-voltage cable failures to assembly mistakes, not the cable. That's a striking number, and it points to something important. The reliability of your MV system isn't determined in the factory. It's determined by the quality of the workmanship at every termination and splice—and by whether the right materials were on hand to do the job correctly.

Where Terminations Go Wrong

A medium-voltage termination is a small piece of precision work. Inside the cable is a layered system—conductor, insulation, a semi-conductive screen, and a metallic shield—engineered to control the electric field. When a cable is cut and terminated, that field has to be managed deliberately, or it concentrates at the cut edge and slowly destroys the insulation. The most common field failures all trace back to a few avoidable mistakes:

• Nicked insulation or shield. A knife cut a fraction too deep during shield removal creates a stress point that becomes a future failure.

• Wrong cutback length. Too short and the stress cone can't control the field; too long and bare insulation is left over-stressed.

• Improper stress relief. Skipping or unevenly applying stress-control material lets the electric field spike. At 15 kV, local field values can exceed 8–10 kV/mm—more than enough to drive partial discharge and eventual breakdown.

• The semicon screen. That thin semi-conductive layer is the single most critical point in any joint or termination. Get its handling wrong and the rest of the work doesn't matter.

• Loose or poorly crimped connectors. These overheat, arc, and fail—sometimes long after the install passes its acceptance test.

  
  

The hard part is that a flawed termination often works fine on day one. The damage shows up months or years later as partial discharge quietly erodes the insulation, until it lets go.

Two Things That Prevent It: The Right Kit and the Right Hands

Good MV terminations come down to materials and craftsmanship. You need the correct items—rated for the voltage class and matched to the cable—and you need installers who know how to use them to standards like IEEE 48.

This is an area we've invested in. Tech Electric now stocks the termination kits, splices, and rubber goods your crews need, so the right components are available when the job is in front of you instead of weeks out. Having the correct kit on the shelf is half the battle against the rushed, wrong-material installs that cause failures.

The other half is training—and we're addressing that too. We'll be offering hands-on termination and splicing training classes soon, designed to help crews build terminations that pass acceptance testing and stay reliable for the life of the cable.

The Bottom Line

The cable will almost always outlast the termination. If you want a medium-voltage system you can trust, focus your attention—and your quality control—on the ends. Purchase the right accessories, train the hands making the connections, and you eliminate the largest single cause of MV cable failure before it ever happens.