Power and current
20 kW to Amps at 415 V: Three-Phase Worked Example
At 415 V three phase, 20 kW electrical input gives 34.78 A at power factor 0.80; shaft output requires an efficiency adjustment.
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Learn the calculation before you use it
Practical engineering explainers, worked examples and field notes. Every article links to a relevant tool and makes its assumptions and limits clear.
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Choose a path when several formulas depend on the same voltage, current or equipment assumptions.
Three-phase voltage, current and neutral: a practical route →
A three-phase answer depends on where voltage and current are measured. This route starts at the conductors and ends with the limits of the balanced model.
Transformer ratings, full-load current and measured loading →
A transformer nameplate, a calculated full-load current and a measured loading percentage describe different things. Follow them in that order.
Voltage drop and conductor data: choose the right method →
A voltage-drop result is only as useful as its conductor data and route assumptions. Choose a method that matches the information you actually have.
Power and current
Power and current
Amps to kW: 230 V and 415 V Worked Examples
Ten amperes gives 1.84 kW at 230 V single phase or 5.75 kW at 415 V three phase when PF is 0.80.
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Power and current
Amps to kWh: Worked Examples at 230 V and 415 V
Amps are a snapshot of current; kWh needs active power and time. Work through one single-phase and one three-phase operating interval.
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Power and current
Balanced three-phase current: the preliminary calculation
A transparent explanation of the familiar √3 relationship, the voltage that belongs in it and the conditions under which it is useful.
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Power and current
How much kVAr is needed to improve power factor?
The kVAr formula is straightforward. Choosing equipment safely still requires harmonic, resonance and switching studies.
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Power and current
How to convert kW to amps for preliminary electrical work
A practical guide to the relationship between power, voltage, power factor, efficiency and line current.
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Power and current
How to estimate kW from amps without hiding the assumptions
Current alone is not power. Voltage, phase arrangement and power factor determine what a measured ampere value can tell you about kW.
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Power and current
kW, kVA and kVAr: what each number tells you
These three quantities are related, but they answer different questions about an AC load and its effect on the supply.
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Power and current
Three-Phase Neutral Current: Formula and Worked Example
100 A, 80 A and 60 A produce a 34.64 A fundamental neutral-current estimate at 120° separation; harmonics need a separate check.
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Power and current
Transformer full-load current on the primary and secondary sides
A transformer keeps approximately the same apparent-power rating across both sides, but current changes as voltage changes.
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Power and current
Why √3 appears in three-phase power calculations
The √3 factor is geometry, not a memorised correction. It connects phase quantities with line quantities in a balanced system.
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Power and current
Why current rises when power factor falls
Power factor changes current without changing the active kW requirement. A short table makes the effect easy to see.
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Power and current
Can Power-Factor Correction Reduce kWh or Only kVA Charges?
A lower kVA demand can affect some tariffs, but it does not automatically reduce a meter's kWh total or every electricity bill.
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Power and current
Does a 20 kW Motor Use 20 Electricity Units per Hour?
Twenty kilowatts on a motor is not automatically twenty kilowatt-hours on the meter every hour; rating basis and actual loading matter.
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Power and current
Horsepower to electrical input: where efficiency belongs
A motor’s shaft output is smaller than its electrical input. Correct conversion begins by identifying which side of the machine the rating describes.
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kVA to Amps: Single-Phase and Three-Phase Worked Examples
The same kVA rating produces different current at different voltages. Start with the phase arrangement and the voltage reference.
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Power and current
Line Current vs Phase Current in Star and Delta Connections
Star: line current equals winding current. Delta: line current is √3 times branch current, assuming balanced sinusoidal operation.
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Power and current
Line-to-Line vs Line-to-Neutral Voltage: Formula and Examples
In an ideal balanced star system, line-to-line voltage is √3 times line-to-neutral voltage. The measurement points still matter.
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Power and current
Power Factor and Motor Efficiency Are Not the Same Number
Both affect a motor-current estimate, but at different steps. Mixing them can hide the power basis or apply a factor twice.
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Single-Phase Current Calculation: kW and kVA Examples at 230 V
Single-phase current depends on what the power rating means. Electrical kW, apparent kVA and mechanical output need different inputs.
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Measurements and equipment
A clamp meter shows amps, not kW
The clamp reading is valuable, but it is one input. Voltage, phase arrangement, power factor and timing complete the power estimate.
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Measurements and equipment
How to Read an Electric Motor Nameplate Before Calculating Current
A nameplate already contains many of the assumptions a calculator would otherwise have to guess. Read them as one matched rating set.
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Measurements and equipment
Reading a Third-Harmonic Current Measurement Before Using It
A display that says 100 A is not telling you the third-harmonic current. Find the spectrum's actual third-order RMS row first.
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Measurements and equipment
What Is a Normal Neutral Current in a Three-Phase System?
A balanced fundamental can cancel in the neutral while harmonic current remains. Interpret the reading before comparing it with a simple calculation.
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Measurements and equipment
What Transformer Percentage Impedance on the Nameplate Means
The %Z printed on a transformer is not a voltage-drop target. It describes an impedance measurement at a defined test condition.
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Measurements and equipment
A Changing Load Needs More Than One Amps-to-kWh Reading
A pump that starts, idles and runs at full load does not draw one current all day. A short interval worksheet gives a more honest energy estimate.
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Measurements and equipment
A True-RMS Clamp Reading Is Not a Harmonic Spectrum
True-RMS is valuable for a distorted current waveform, but it does not identify which frequency components produced the number.
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Neutral Current Measurement: Why the Reading Can Differ from the Calculation
Three phase-current magnitudes are not the whole waveform. A neutral reading can expose assumptions that a simple calculation cannot represent.
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Transformer Loading Percentage: Formula and 100 kVA Example
At 415 V and 100 A on a balanced three-phase 100 kVA transformer, apparent-power loading is about 71.88% of nameplate.
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Measurements and equipment
Why Transformers Are Rated in kVA Instead of kW
The same 100 kVA can accompany 80 kW at PF 0.80 or 95 kW at PF 0.95. The nameplate is not a fixed kW output.
Read article →Protection and project workflow
Protection and project workflow
Breaker current rating is not breaking capacity
A 32 A breaker label tells you about nominal current. It does not say the device can interrupt every possible fault at that point.
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Protection and project workflow
Building a load schedule that shows demand and phase balance
A load schedule should explain where its totals came from, not just produce one large kW number at the bottom.
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Protection and project workflow
How cable correction factors combine
Correction factors multiply. Their source conditions and applicability matter as much as the arithmetic.
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Protection and project workflow
Ib ≤ In ≤ Iz Worked Examples: Compare Breaker and Cable Currents
23 A ≤ 25 A ≤ 28 A passes this preliminary current comparison; a 32 A breaker with the same cable capacity does not.
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Protection and project workflow
Ib, In and Iz: the three currents in a basic breaker check
The three symbols describe load, protective device and conductor. Keeping them separate prevents circular sizing logic.
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Protection and project workflow
A preliminary Ib ≤ In ≤ Iz breaker relationship check
Ib, In and Iz are a useful first check, but they do not determine breaking capacity, selectivity or fault protection.
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Protection and project workflow
Transformer Fault Current: What the Infinite-Source Shortcut Leaves Out
Dividing full-load current by %Z is useful for understanding a transformer, but the available fault current at a board needs more information.
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Protection and project workflow
Transformer Percentage Impedance and Fault Current: A Worked Estimate
A percentage impedance can turn rated current into a rough terminal-fault estimate, but source and circuit impedances change the real result.
Read article →Voltage drop and conductors
Voltage drop and conductors
How far can this cable run before voltage drop exceeds the target?
Maximum route length is an inverse voltage-drop calculation, not a complete cable-sizing decision.
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Voltage drop and conductors
mV/A/m Voltage Drop: Formula, Units and Worked Example
mV/A/m means millivolts per ampere per metre. The value must match the cable and circuit arrangement in its source data.
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Voltage drop and conductors
Three-Phase Voltage Drop Formula and Worked Example
A substituted example shows where √3, route length, resistance, reactance and power factor enter the result.
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Voltage drop and conductors
Voltage drop: route length, conductor data and useful checks
Voltage drop is easy to calculate badly. The important work is choosing matching conductor data, geometry and route length.
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Voltage drop and conductors
Conductor Resistance vs Temperature: Formula and Example
In an illustrative copper model, resistance rises about 23.6% from 20°C to 80°C; ambient air alone does not tell you conductor temperature.
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Voltage drop and conductors
Copper and aluminium in preliminary conductor calculations
Material changes resistance, but a practical cable choice also involves size, joints, installation, thermal behavior and product data.
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Voltage drop and conductors
Measured Versus Calculated Voltage Drop on a Feeder
A calculated drop and a field reading are only comparable when the measurement points, load current and operating condition match.
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Voltage drop and conductors
One-way route length versus total conductor length
Length errors often come from counting the return path twice. Start by identifying the geometry built into the selected formula or coefficient.
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Voltage drop and conductors
Parallel cable runs: what changes in a voltage-drop calculation
Two identical paths can halve effective impedance in a simple model. Unequal paths do not automatically share current equally.
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Voltage drop and conductors
Preliminary cable sizing with your own engineering data
Cable sizing is a comparison of constraints, not a lookup of load current against one universal table.
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Voltage drop and conductors
Resistance, reactance and power factor in AC voltage drop
R and X do not contribute identically to the in-phase voltage change. Power factor sets the weighting in the common approximation.
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