Transformers & Substations
300 kVA three-phase pad-mounted transformer
361 A at 480 V · 833 A at 208 V · 15 / 25 / 35 kV class
Overview
A 300 kVA three-phase pad-mounted transformer is a liquid-filled, dead-front distribution transformer for ground-level medium-voltage service: a 12.47 / 13.2 / 13.8 kV (15 kV class), 24.94 kV (25 kV class) or 34.5 kV (35 kV class) primary stepping down to 208Y/120, 480Y/277 or 600Y/347 V at 60 Hz. At full load it delivers 361 A at 480 V, 833 A at 208 V or 289 A at 600 V, and draws 13.9 A from a 12.47 kV feeder. Entogo designs and builds the 300 kVA unit to IEEE C57.12.34 / C57.12.28 and DOE 10 CFR 431 in its own factory, ships engineered-to-order units in 16–24 weeks, and offers UL (cULus) / CSA certification on request.
Full-load and primary current
Three-phase line current at rated load: amperes = kVA × 1000 ÷ (√3 × V).
| Winding / voltage | Full-load current |
|---|---|
| Secondary 208Y/120 V | 833 A |
| Secondary 480Y/277 V | 361 A |
| Secondary 600Y/347 V | 289 A |
| Primary 12.47 kV (15 kV class, 95 kV BIL) | 13.9 A |
| Primary 13.2 kV (15 kV class, 95 kV BIL) | 13.1 A |
| Primary 13.8 kV (15 kV class, 95 kV BIL) | 12.6 A |
| Primary 24.94 kV (25 kV class, 125 kV BIL) | 6.9 A |
| Primary 34.5 kV (35 kV class, 150 kV BIL) | 5.0 A |
Available secondary fault current
Three-phase bolted fault at the secondary terminals with an infinite primary source: full-load amps ÷ (%Z ÷ 100). Impedance is a specifier's choice; 5.75 % is common for larger pad-mounted units, lower values below about 500 kVA. Real values are lower once the utility source impedance is included.
| Impedance | 208Y/120 V | 480Y/277 V | 600Y/347 V |
|---|---|---|---|
| 4.00 % | 20.8 kA | 9.0 kA | 7.2 kA |
| 5.00 % | 16.7 kA | 7.2 kA | 5.8 kA |
| 5.75 % | 14.5 kA | 6.3 kA | 5.0 kA |
What a 300 kVA unit typically serves
- Mid-size commercial buildings, schools and clinics
- Multifamily and mixed-use developments
- Light industrial and warehouse service
- Level 2 charging hubs of roughly 10 to 30 ports
Typical, not prescriptive: size from the calculated load and growth margin — see how to size a transformer (kVA selection), and for EV-charging sites the service-capacity calculator.
Custom-engineered · built to order
Lead time
16–24 weeks
Order now for estimated delivery Feb 2027 – Apr 2027.
Certification and testing may extend this, depending on the applicable standard and scope.
FAQ
Common questions
- How many amps is a 300 kVA transformer at 480 V?
- A 300 kVA three-phase transformer delivers 361 A at 480 V full load (kVA × 1000 ÷ (√3 × 480)). At 208 V the same unit delivers 833 A and at 600 V 289 A.
- What is the primary current of a 300 kVA pad-mounted transformer?
- On a 12.47 kV feeder a 300 kVA unit draws 13.9 A at full load; on 13.8 kV 12.6 A, on 24.94 kV 6.9 A and on 34.5 kV 5.0 A.
- How much fault current can a 300 kVA transformer deliver?
- With an infinite primary source, a 300 kVA unit at 480 V and 5.75 % impedance can deliver about 6.3 kA of three-phase bolted-fault current (full-load amps ÷ 0.0575). The real value is lower once the utility's source impedance is included; the switchgear downstream must be rated for the study value, not this ceiling.
- How long does a 300 kVA pad-mounted transformer take to deliver from Entogo?
- 300 kVA pad-mounted units are engineered to order and ship from Entogo's own factory in 16–24 weeks — against the one-to-four-year lead times common in the North-American merchant market. If the order needs new cULus/CSA certification, delivery is within 36 weeks.
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