Use the MGM Transformers’ Phase Calculator to the left to enter any two of kVA, volts, or amps and the tool solves the third. Or use the Configurator below to build a complete quote from phase, voltage, taps, temperature rise, K‑factor, and enclosure information.
A finished catalog code looks like this:
HT112A3B2SH–HK0160LN03RThe calculator uses the standard relationships between power (kVA), voltage (V), and full-load current (amps).
Single-phase:
kVA = (V × A) ÷ 1000 Amps = (kVA × 1000) ÷ V
Three-phase:
kVA = (V × A × 1.732) ÷ 1000 Amps = (kVA × 1000) ÷ (V × 1.732)
Why √3 (1.732)? In a balanced three-phase system the three voltages are 120° apart, and line-to-line voltage equals √3 × line-to-neutral voltage.
Worked example. A 75 kVA three-phase unit at 480 V: 75 × 1000 ÷ (480 × 1.732) = 90.2 A. At 208 V the same 75 kVA draws 208 A.
kVA and amps do not need power factor; kW and kVA do.
Examples. 200 A at 240 V three-phase = 83 kVA. 70 kVA at 480 V three-phase = 84 A. 80 kW at 0.8 PF = 100 kVA.
| Application | Typical PF |
|---|---|
| Data centers (AI/HPC) | 0.85–0.95 |
| Industrial / motor loads | 0.70–0.90 |
| Hospitals | 0.80–0.90 |
| Resistive / heating | ~1.0 |
Example. A 400 A, 240 V three-phase service ≈ 166 kVA minimum → with headroom, a 225 kVA standard unit. Always confirm with a licensed engineer and the NEC.
Single-phase: 1, 1.5, 3, 5, 7.5, 10, 15, 25, 37.5, 50, 75, 100, 167, 250, 333, 500 kVA
Three-phase: 3, 6, 9, 15, 30, 45, 75, 112.5, 150, 225, 300, 500, 750, 1000, 1500, 2000, 2500 kVA
MGM builds general-purpose, dry-type, K-factor, and custom units across this range — many in stock.
Three-phase — A = kVA × 1000 ÷ (V × 1.732)
| kVA | 208V | 240V | 480V | 600V |
|---|---|---|---|---|
| 15 | 41.6 | 36.1 | 18.0 | 14.4 |
| 30 | 83.3 | 72.2 | 36.1 | 28.9 |
| 45 | 124.9 | 108.3 | 54.1 | 43.3 |
| 75 | 208.2 | 180.4 | 90.2 | 72.2 |
| 112.5 | 312.3 | 270.6 | 135.3 | 108.3 |
| 150 | 416.4 | 360.8 | 180.4 | 144.3 |
| 225 | 624.5 | 541.3 | 270.6 | 216.5 |
| 300 | 832.7 | 721.7 | 360.8 | 288.7 |
| 500 | 1387.9 | 1202.8 | 601.4 | 481.1 |
Single-phase — A = kVA × 1000 ÷ V
| kVA | 120V | 240V | 480V |
|---|---|---|---|
| 5 | 41.7 | 20.8 | 10.4 |
| 15 | 125.0 | 62.5 | 31.2 |
| 25 | 208.3 | 104.2 | 52.1 |
| 50 | 416.7 | 208.3 | 104.2 |
| 75 | 625.0 | 312.5 | 156.2 |
| 100 | 833.3 | 416.7 | 208.3 |
Need full 600V-class and medium-voltage charts? Download our reference documents.
For transformers rated 1000 V or less, NEC Table 450.3(B) sets the maximum overcurrent device rating as a percentage of rated full-load current. Simplified guidance:
| Protection method | Primary | Secondary |
|---|---|---|
| Primary only (primary FLA ≥ 9 A) | ≤ 125% | n/a |
| Primary & secondary (secondary FLA ≥ 9 A) | ≤ 250% | ≤ 125% |
| Primary only (primary FLA 2–9 A) | ≤ 167% | n/a |
| Primary only (primary FLA < 2 A) | ≤ 300% | n/a |
Where 125% doesn’t match a standard device size, the next higher standard rating is permitted. Simplified summary — always size to the current NEC edition and your AHJ.
A transformer’s nameplate impedance (%Z) sets the available short-circuit current on the secondary:
Available fault current ≈ secondary FLA ÷ (%Z ÷ 100)
Example. A 500 kVA, 480 V unit (FLA 601 A) at 5% impedance delivers roughly 601 ÷ 0.05 = 12,000 A — size secondary breakers and conductors for that available fault current.
Use single-phase mode for residential, light-commercial, and control-power loads; use three-phase mode for most industrial and commercial distribution.
At the same kVA and voltage, a three-phase unit draws lower current per line because of the √3 factor — which is why three-phase distribution is more efficient for larger loads.
A step-up transformer raises voltage (240 V → 480 V); a step-down lowers it (480 V → 208 V).
Buck-boost transformers make small corrections (typically 5–20%, e.g. 208 V → 240 V) and are sized by load amps and voltage change — far smaller and cheaper than an isolation transformer for minor adjustments.
Common corrections: 208→240 V, 240→208 V, 480→600 V. See our buck-boost transformers.
More terms in our transformer glossary.
Enter any two of kVA, volts, or amps — the tool solves the third.