Philippine Electrical Code – Ambient Correction Factor for Cables

Temperature in the Philippines

According to PAGASA data, the average mean annual temperature across all weather stations in the Philippines, excluding Baguio, is 26.6°C. The coolest month is January, with an average temperature of 25.5°C, while May is the warmest month, averaging 28.3°C. Latitude has little impact on temperature variations, whereas altitude significantly influences temperature. For instance, Baguio, situated at an elevation of 1,500 meters, has a mean annual temperature of 18.3°C. This cooler climate, comparable to temperate regions, has earned Baguio the title of the "Summer Capital of the Philippines."

The difference in mean annual temperatures between Zamboanga, the southernmost station, and Laoag, the northernmost station, is negligible. This indicates that areas in Luzon, Visayas, and Mindanao located at or near sea level experience similar mean annual temperatures.

Hottest Day on Record in the Philippines

Tuguegarao, Cagayan Valley, holds the record for the highest temperature in the Philippines, reaching 42.2°C on both April 22, 1912, and May 11, 1969. Meanwhile, Metro Manila experienced its hottest day on May 14, 1987, with a temperature of 38.5°C.

According to PAGASA, the mean annual temperature across the Philippines, excluding Baguio, is 26.6°C. May is typically the warmest month, with an average temperature of 28.3°C.

Ambient Temperature Correction Factors

The Philippine Electrical Code (PEC) requires ambient temperature correction factors to ensure that conductors do not overheat under varying environmental conditions. These factors adjust the allowable ampacity of conductors based on the ambient temperature at the installation site.

Conductors heat up when carrying current. Elevated ambient temperatures increase the risk of overheating. Correction factors help maintain conductor performance and safety. Ambient temperature correction factors are detailed in PEC Table 3.10.2.6(B)(2)(a) and applied to ampacity values in tables such as Table 3.10.2.6(B)(16).

When to Apply Ambient Temperature Correction Factors

Anytime the ambient temperature differs from the baseline of 30°C, as listed in PEC ampacity tables.

Determine the conductor’s base ampacity from PEC Table 3.10.2.6(B)(16).
Apply the correction factor from Table 3.10.2.6(B)(2)(a) for the actual ambient temperature.

Example:
A conductor with a base ampacity of 100A and an ambient temperature of 40°C (104°F) has a correction factor of 0.91 (for 75°C insulation). The corrected ampacity would be:
100 A × 0.91 = 91 A

Insulation Types:
The correction factor depends on the conductor insulation type, such as 60°C, 75°C, or 90°C ratings.

Special Considerations:
Locations like rooftops where conductors are exposed to sunlight may have additional adjustment factors per 3.10.2.6(B)(3)(c).

Recommendation

Based on the highest temperature recorded in the Philippines, it is recommended to consider temperatures 41°C - 45°C. However, it is still the Electrical Engineer's decision which temperature is best suitable for the project.