A professional-grade chart (like those from Southwire, Okonite, or Prysmian) goes far beyond copper vs. aluminum. A good chart provides:
If you work with 5kV to 35kV distribution systems, a medium voltage (MV) cable size chart is indispensable. However, unlike low-voltage charts where "ampacity" is the main event, an MV chart is a layered document involving insulation type, shielding, grounding, and soil temperature. This review breaks down what these charts do well, where they fall short, and how to use them without creating a hazard.
Medium voltage cables are generally categorized by their voltage class. The most common in industrial applications are: 15kV 25kV 35kV medium voltage cable size chart
(Essential tool, but dangerous if used without context)
Ampacity varies based on installation method (air, duct, or direct burial) and ambient temperature. Always consult the manufacturer's specific data sheet. Key Factors in Selecting Your Cable Size 1. Voltage Drop However, unlike low-voltage charts where "ampacity" is the
If cables are bundled together or installed in areas with high ambient soil temperature, their ability to dissipate heat decreases. In these cases, you must apply , which effectively lower the allowable ampacity of the cable. Summary Checklist for Engineers
Download the free ampacity calculator from Okonite or Nexans . Their charts include the hidden derating factors that printed tables miss. For a quick reference, IEEE 835 is the gold standard, but it's dense. The most common in industrial applications are: 15kV
: Ampacity varies significantly whether cables are in air , direct-buried , or in underground ducts .
: Higher voltage ratings (e.g., 35kV vs 5kV) require thicker insulation, which increases the cable's overall diameter and weight even for the same conductor size.
On long runs, the resistance of the cable causes voltage to drop by the time it reaches the load. For MV systems, it is standard practice to keep the voltage drop below . If your run is exceptionally long, you may need to "upsize" the cable beyond what the ampacity chart suggests. 2. Short Circuit Rating