IEEE C57.13 Clause 4.2 states that the dielectric strength of air decreases as altitude decreases. The dielectric strength on air should be multiplied by the altitude correction factor provided in Table 1.

Dieletric strength is the property of a medium, in this case air, to exhibit negligible or no electrical conductivity thus acting as an insulator.

Table 1 - Dielectric strength correction factors for altitudes greater than 1000 m
Altitude meters Altitude correction factor for dielectric strength
1000 1.00
1200 0.98
1500 0.95
1800 0.92
2100 0.89
2400 0.86
2700 0.83
3000 0.80
3600 0.75
4200 0.70
4500 0.67
NOTE - An altitude of 4500 m is considered a maximum for instrument transformers conforming to this standard (IEEE C57.13).

Table 1 indicates that at an altitude of 1000 m or below, the dielectric strength correction factor is 1.0. This means that even the tallest building in the world, the Burj Khalifa which is 828 m tall, there will still be no reduction in the dielectric strength of air. It will be different however, if you install an electrical equipment on highlands such as Leadville, Colorado with an elevation of 10,430 feet (3179 m) where the multiplying factor will be 0.75.

Reduced dielectric strength of air means that its insulating property is reduced requiring increased clearances between phases and/or ground (earth) leading to larger electrical equipment size. Larger equipment physical size will comparatively increase its cost.


  • A Filipino Engineer, Registered Professional Engineer of Queensland (RPEQ) - Australia, and Professional Electrical Engineer (PEE 2574 - 1st Place April 1991) - Philippines with extensive experience in concept selection, front-end engineering, HV & LV detail design, construction, and commissioning of Hazardous and Non-Hazardous Area electrical installations in water and wastewater pipeline and pumping facilities, offshore platforms, hydrocarbon process plants and pipelines including related facilities. Hazardous area classification and design certification (UEENEEM015B, UEENEEM016B, UEENEEM017B).



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