Things about motors – it is often said that a 1-square-millimeter cable can handle a current of 5 amperes. But in a triangular connection, does it refer to line current or phase current?

The rated voltage of a motor is the line voltage, and its rated current is the line current. \"When a motor’s nameplate indicates currents for two different connection methods\"... the current value indicated for that motor is the rated current; however, this rated current applies to two different voltages. Since the voltage applied to the motor’s windings (when it is operating at its rated power) remains constant, the currents corresponding to the two connection methods must relate to two different rated voltages – such a motor is a dual-power motor. 10 down five, 100 up two ； 25, 35: Four, Three Realms ； 70, 95: Two and a half times ； Tube insertion, temperature: 20-30% discount ； Double the value for bare wires; an upgrade to copper wire is considered as well. This formula is based on the use of aluminum-core insulated wires installed in exposed locations, with an ambient temperature of 25 degrees. It provides the current-carrying capacity in amperes for wires of various cross-sectional areas. Hello, if you can understand the formula above, you will be able to make the necessary conversions. The second mnemonic ； 2.5 times 9, then subtract one and move upward in sequence. Thirty-five times 3.5, pair them up and subtract 0.5. If conditions change, a discount is applied; at high temperatures, copper upgrades at a 10% discount. Two, three, four roots in the tube; 80%, 70%, 60% capacity for current conduction. Here’s the third one for you ； Given the transformer capacity, the rated current at each voltage level can be determined using the following formula: divide the capacity by the voltage value; multiply the result by six and then divide by ten. Note: Suitable for any voltage level. In daily work, some electricians are only involved in calculating the rated current of transformers for one or two voltage levels. By simplifying the above mnemonic, a mnemonic for calculating the rated current on each voltage level can be derived: multiply the capacity coefficients. Given the transformer capacity, it is possible to quickly calculate the current values of the primary and secondary protection fuses (commonly known as insurance fuses). Mnemonic b: For high-voltage fuses in distribution transformers, calculate by comparing capacity and voltage. For low-voltage fuses in distribution transformers, use capacity multiplied by 9 and divided by 5. Note: The proper selection of fusing elements is of great significance for the safe operation of transformers. When fuses are used solely for protecting the high and low voltage sides of a transformer, the proper selection of the fuses becomes even more important. This is a problem that electricians often encounter and need to solve. Given the capacity of a three-phase motor, to find its rated current: Rule (c): Divide the capacity by the voltage in kilovolts; multiply the result by 0.76. Note: (1) This mnemonic is applicable to the calculation of the rated current of three-phase motors at any voltage level. Both formulas and memorized rules show that motors with the same capacity but different voltage levels have different rated currents; in other words, when the voltage in kilovolts varies, dividing by the same capacity yields different \"quotients.\" When these different quotients are multiplied by the same coefficient of 0.76, the resulting current values also differ. If the above mnemonic is referred to as a general mnemonic, then special calculation mnemonics can be derived for determining the rated current of motors operating at voltage levels of 220 V, 380 V, 660 V, and 3.6 kV. When using these special calculation mnemonics to find the rated current of a three-phase motor, the relationship between capacity in kilowatts and current in amperes is based on simple multiplication; there is no need to divide the capacity by the voltage in kilovolts and then multiply the result by the coefficient 0.76. Three-phase 220V motor, 3.5 kilowatts and 3.5 amperes. The commonly used motor is a 380V model, with one kilowatt and two amperes. Low-voltage 660 motor, 1.2 kilowatts and amperes. 3,000-volt high-voltage motor, four kilowatts one ampere. High-voltage 6,000-volt motor, eight kilowatts one ampere. (2) When using mnemonic c, the capacity unit is kW, the voltage unit is kV, and the current unit is A; this point must be kept in mind. (3) The coefficient 0.76 in formula c is a comprehensive value derived from calculations taking into account the motor’s power factor and efficiency, etc. The power factor is 0.85 and the efficiency is 0.9; these two values are more appropriate for motors with a capacity of several dozen kilowatts, while they seem excessive for commonly used motors with a capacity of less than 10 kW. In this case, the rated current of the motor calculated using formula c differs from the value indicated on the motor’s nameplate; this difference has little impact on motors of 10 kW or less, as it affects the switch, contactor, wires, etc., based on the rated current. (4) Use mnemonic calculation techniques. To calculate the rated current of a common 380V motor using a mnemonic, first divide the motor’s supply voltage of 0.38 kV by 0.76; then multiply the resulting quotient by the motor’s capacity in kW. For larger 6kV motors, if the capacity in kW is exactly a multiple of 6kV, the capacity is divided by the voltage in kV, and the resulting figure is multiplied by a coefficient of 0.76. (5) Error. The coefficient 0.76 in formula c is derived by assuming a motor power factor of 0.85 and an efficiency of 0.9; as a result, calculating the rated current for motors with different power factors and efficiencies leads to errors. The multiples of capacity (kW) and current (A) for the 5 specialized formulas derived from formula c are the quotient of the voltage level (kV) value divided by the 0.76 coefficient. Special mnemonics are simple for mental calculation, but it should be noted that their error margin increases. Generally, for units with a higher power rating, the calculated current is slightly higher than that indicated on the nameplate ； For those with a lower kilowatt rating, the calculated current is slightly lower than that indicated on the nameplate. Therefore, when calculating the current, if it reaches ten or several dozen amperes, there is no need to consider values beyond the decimal point. It is possible to round off rather than use half-values, taking only whole numbers; this is simple and does not affect usability. For smaller currents, it is sufficient to consider one decimal place. *To determine capacity by measuring current: Measure the no-load current of a motor without a nameplate, and use this value to estimate its rated capacity. Mnemonic: For a motor without a nameplate, measure its no-load current, multiply by ten and divide by eight to get an approximate value in kilowatts. Note: This mnemonic provides a method for estimating the capacity in kilowatts of a three-phase asynchronous motor without a nameplate, by measuring the motor’s no-load current. To determine the load capacity of a power transformer by measuring the current on its secondary side: Rule of thumb: Given the secondary voltage of the transformer, measure the current to find the power in kilowatts. Voltage level: 400 volts, 1 ampere, 0.6 kilowatts. Voltage level: 3,000 volts; power: 1 ampere at 4.5 kilowatts. Voltage level: 6,000 volts; power: exactly 9 kilowatts per ampere. Voltage level: 10 kV; current: 1 A; power: 15 kW. Voltage level: 35 kV, 1 ampere at 55 kilowatts. Note: (1) In their daily work, electricians often encounter situations where higher-level departments or managers ask about the operation status of power transformers and what the load level is The electrician himself often needs to know what the load on the transformer is. The load current is easy to determine; it can be seen directly from the ammeter installed on the distribution device, or measured using a corresponding clamp meter. However, the load power cannot be seen or measured directly. This requires the use of this mnemonic to carry out the calculations; otherwise, using conventional formulas would be both complicated and time-consuming. (2) “Voltage level: 400 volts; one shot: 0.6”