Calculation of conductor current carrying capacity - Database & Sql Blog Articles

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1. Use: The current carrying capacity (safe current) of various conductors can usually be found in the manual. However, with a simple method and some mental math, you can calculate it directly without looking up tables. The current carrying capacity of a wire depends on its cross-sectional area, material (aluminum or copper), type (insulated or bare), installation method (open or in conduit), and ambient temperature (around 25°C or higher). These factors make the calculation more complex.

10 Next five, 1 0 0 Upper two.

2 5 , 3 5 , four or three circles.

7 0 , 95 , two and a half times.

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Add half of the bare wire.

Copper wire upgrade count.

4. Description: This rule applies to aluminum core insulated wires under an ambient temperature of 25°C. If conditions differ, adjustments are made accordingly. Insulated wires include rubber or plastic insulated types. The current carrying capacity is not directly stated but expressed as a multiple of the cross-sectional area. Familiarizing yourself with standard wire sizes is essential:

1, 1.5, 2.5, 4, 6, 10, 16, 25, 35, 50, 70, 95, 120, 150, 185...

Aluminum core insulated wires typically start at 2.5 mm², while copper starts at 1 mm². Bare aluminum starts at 16 mm², and bare copper at 10 mm². The "rule of thumb" suggests that for aluminum core insulated wires, the current carrying capacity is calculated based on the cross-section size. The numbers indicate the wire size in mm², and the Chinese characters represent the multiplier. For example:

10 and below: 5 times the cross-section

100 and above: 2 times the cross-section

25 and 35: 4 times and 3 times respectively

70 and 95: 2.5 times

For instance:

[Example 1] A 6 mm² wire has a current capacity of 30 A (6 × 5 = 30).

[Example 2] A 150 mm² wire has a capacity of 300 A (150 × 2 = 300).

[Example 3] A 70 mm² wire has a capacity of 175 A (70 × 2.5 = 175).

These rules are approximate and may vary slightly depending on actual conditions. For example, a 25 mm² wire is rated at 100 A according to the rule, but the actual value might be slightly less. Similarly, a 35 mm² wire could be rated at 105 A, but the real value may be higher. These small discrepancies generally do not affect practical use.

If the wire is installed in a conduit (or covered), a 20% reduction is applied (multiply by 0.8). If the ambient temperature exceeds 25°C, a 10% reduction is used (multiply by 0.9). In cases where both conditions apply, a 30% reduction is used (multiply by 0.7).

For example:

A 10 mm² aluminum wire in a conduit: 10 × 5 × 0.8 = 40 A.

A 95 mm² aluminum wire in a hot environment: 95 × 2.5 × 0.9 = 213.8 A.

Bare aluminum wires have their current capacity increased by 50% (multiply by 1.5). For example:

A 16 mm² bare aluminum wire: 16 × 4 × 1.5 = 96 A.

A 35 mm² bare aluminum wire: 35 × 3 × 1.5 = 157.5 A.

Copper wires are upgraded by one size before applying the same calculation as for aluminum wires. For example:

A 35 mm² bare copper wire is treated as 50 mm² aluminum: 50 × 3 × 1.5 = 225 A.

A 16 mm² copper insulated wire is treated as 25 mm² aluminum: 25 × 4 = 100 A.

A 95 mm² copper insulated wire is treated as 120 mm² aluminum: 120 × 2 × 0.8 = 192 A.