How to calculate current in wires
In electrical engineering and household electricity, it is crucial to correctly calculate the current of wires, which is directly related to electrical safety and equipment life. This article will combine hot topics and hot content in the past 10 days, introduce the calculation method of wire current in detail, and provide structured data for easy understanding.
1. Basic principles of current calculation
According to Ohm's law, current (I) is equal to voltage (U) divided by resistance (R), which isI=U/R. But in actual applications, the current calculation of the wire also needs to consider the power (P) and load type. Here are common formulas:
| Computing scenarios | formula | illustrate |
|---|---|---|
| DC circuit | I=P/U | Power (P) divided by voltage (U) |
| Single phase AC circuit | I = P / (U × cosφ) | cosφ is the power factor (usually 0.8-1) |
| Three-phase AC circuit | I = P / (√3 × U × cosφ) | √3 is the three-phase coefficient (about 1.732) |
2. Factors affecting the current carrying capacity of wires
The current (carrying capacity) allowed to pass through a wire is affected by many factors. The following are the key points that have been hotly debated in the past 10 days:
| Influencing factors | Specific instructions | Typical value reference |
|---|---|---|
| Wire material | Copper wire carrying capacity >Aluminum wire | Copper wire: 5-8A/mm²; Aluminum wire: 3-5A/mm² |
| Wire cross-sectional area | The larger the cross-sectional area, the higher the carrying capacity | The carrying capacity of 1.5mm² copper wire is about 15A |
| Laying environment | Open wires dissipate heat better than dark wires | The open wire carrying capacity can be increased by 20-30% |
| ambient temperature | For every 1℃ increase in temperature, the current carrying capacity decreases by 0.5% | Derating is required at 40℃ |
3. Practical application cases
Taking the recently hotly discussed "home air conditioning installation" as an example, calculate the current demand of a 1.5 HP air conditioner (approximately 1100W):
| step | Calculation process | result |
|---|---|---|
| 1. Determine the power | P = 1100W | 1100W |
| 2. Select voltage | Household single phase 220V | U=220V |
| 3. Calculate current | I = P / (U × cosφ) = 1100 / (220×0.9) | ≈5.56A |
| 4. Select wires | 1.5mm² copper wire (carrying capacity 15A) | meet needs |
4. Answers to recent hot questions
1.“What size wires are used for new energy vehicle charging piles?”
7kW charging pile (single-phase 220V): current is about 32A, requiring 4-6mm² copper wire.
11kW charging pile (three-phase 380V): current is about 16A, requiring 2.5-4mm² copper wire.
2."Standards for Renovation of Electrical Wires in Old Residential Areas"
According to the latest national standards, it is recommended that the main line ≥10mm² copper wire and the branch line ≥2.5mm² copper wire.
3."Is it normal for the wires to be hot?"
A slight fever is normal, but if the temperature exceeds 60°C, check whether the load exceeds the standard.
5. Safety precautions
1. When selecting wires, a 20% margin must be reserved to avoid full load operation.
2. In long-term high-current scenarios (such as electric water heaters), it is recommended to use high-standard wires.
3. Regularly check whether the wire insulation layer is aging, especially for lines that have been used for more than 10 years.
Through the above structured data and case analysis, I believe you have mastered the calculation method of wire current. In actual operation, it is recommended to consult a professional electrician to ensure the safety of electricity use.
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