1. Select the cross section according to the temperature rise of the core
When the load current is passed, the core temperature does not exceed the long-term working temperature allowed by the cable insulation. That is to say, select according to the allowable current-carrying capacity.
Suggestion: The cable passes through different heat dissipation conditions. The corresponding core operating temperature will be different, and the section should be selected according to the area with severe heat dissipation conditions (usually no more than 1 meter).
2. Select the cross section according to the allowable range of voltage loss
When the terminal voltage of the electrical equipment actually deviates from the rated value, its performance will be affected, and the extent of the impact will be determined by the magnitude and duration of the voltage deviation.
Suggestion: The voltage loss increases due to the sharp rise of the core temperature during fire. The voltage loss should be calculated according to the fire conditions to ensure the continuous operation of important equipment. Due to the excellent heat insulation and heat dissipation characteristics of BTLY products, it is only necessary to enlarge the cable selected according to the normal situation by one to two. Usually, it can meet the condition that the voltage deviation under fire conditions is not more than -10%.
Three, select the cross section according to the economic current
The total cost during the economic life is small. That is, the initial investment and the cost of line loss during the economic life are small.
The so-called economic current is the working cable (range) corresponding to the applicable cross-section (range) during the life of the cable, the sum of investment and conductor loss costs. For details, please refer to “Low Voltage Cable Economic Current Density Range Table”.
Suggestion: BTLY products should have good heat dissipation characteristics. If the cross section is selected according to the temperature rise of the core, the selection can be reduced by one level. But taking into account the economic current factor. Therefore, it is not recommended. If selected in accordance with the routine, the line loss will be reduced by 4-7%, which is of great economic significance.
Fourth, the selection of the cross section of the neutral power cable and the ground wire
(1) In a single-phase two-wire circuit, regardless of the size of the phase wire cross section, the neutral wire and ground wire should be the same cross section as the phase wire.
(2) In the three-phase five-wire power distribution system, the allowable current carrying capacity of the neutral wire and ground wire should not be less than the sum of the large unbalanced load current and harmonic current in the line. When the phase wire core is not larger than 16mm2, the neutral wire and ground wire should have the same cross-section as the phase wire. When the phase wire core is larger than 16mm2, if the neutral wire current is small, the cross section of the phase wire can be selected, but it should not be less than 50% of the phase wire cross section and not less than 16mm2.
Suggestion: Use the aluminum metal sheath in the BTLY cable as the grounding core. The aluminum pipe grounding wire is connected by a dedicated connector, and the connection is firm and reliable. The equivalent resistance of the aluminum tube section of the BTLY cable meets the grounding needs of the corresponding copper core