Oil-Filled Transformer Full Load Amps Chart: Complete FLA Reference

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Comprehensive full load amperage chart for oil-immersed distribution transformers. Find FLA values for all
standard kVA ratings at common voltages, plus wire sizing recommendations.

⚡ FLA Calculation Formulas

Single-Phase:
FLA = (kVA × 1000) ÷ Voltage		Three-Phase:
FLA = (kVA × 1000) ÷ (Voltage × √3)

Knowing the Full Load Amperage (FLA) of your oil-filled transformer is essential for proper
conductor sizing, fuse selection, and protection coordination. This chart provides FLA values at
all common secondary voltages including 600V for Canadian applications.

Single-Phase Oil-Filled Transformer FLA Chart

Full load amperage for single-phase oil-filled transformers at common secondary voltages:

kVAFull Load Amps (FLA) by Secondary VoltageSpecs
120V208V240V277V480V600V
10 kVA83.3 A48.1 A41.7 A36.1 A20.8 A16.7 AView
→
15 kVA125.0 A72.1 A62.5 A54.2 A31.2 A25.0 AView
→
25 kVA208.3 A120.2 A104.2 A90.3 A52.1 A41.7 AView
→
37.5 kVA312.5 A180.3 A156.2 A135.4 A78.1 A62.5 AView
→
50 kVA416.7 A240.4 A208.3 A180.5 A104.2 A83.3 AView
→
75 kVA625.0 A360.6 A312.5 A270.8 A156.2 A125.0 AView
→
100 kVA833.3 A480.8 A416.7 A361.0 A208.3 A166.7 AView
→
167 kVA1391.7 A803.0 A695.8 A602.9 A347.9 A278.3 AView
→
250 kVA2083.3 A1201.9 A1041.7 A902.5 A520.8 A416.7 AView
→
333 kVA2775.0 A1600.9 A1387.5 A1202.2 A693.8 A555.0 AView
→
500 kVA4166.7 A2403.8 A2083.3 A1805.1 A1041.7 A833.3 AView
→

Three-Phase Oil-Filled Transformer FLA Chart

Full load amperage for three-phase oil-filled transformers. Note: Three-phase FLA is calculated
using the √3 (1.732) factor.

kVAFull Load Amps (FLA) by Secondary VoltageSpecs
208V240V277V480V600V
15 kVA41.6 A36.1 A31.3 A18.0 A14.4 AView
→
30 kVA83.3 A72.2 A62.6 A36.1 A28.9 AView
→
45 kVA124.9 A108.3 A93.8 A54.1 A43.3 AView
→
75 kVA208.2 A180.4 A156.4 A90.2 A72.2 AView
→
112.5 kVA312.3 A270.6 A234.6 A135.3 A108.2 AView
→
150 kVA416.4 A360.8 A312.8 A180.4 A144.3 AView
→
225 kVA624.6 A541.3 A469.2 A270.6 A216.5 AView
→
300 kVA832.8 A721.7 A625.6 A360.8 A288.7 AView
→
500 kVA1388.0 A1202.8 A1042.6 A601.4 A481.1 AView
→
750 kVA2082.0 A1804.2 A1564.2 A902.1 A721.7 AView
→
1000 kVA2776.0 A2405.6 A2085.5 A1202.8 A962.3 AView
→
1500 kVA4164.0 A3608.4 A3128.3 A1804.2 A1443.4 AView
→
2000 kVA5552.0 A4811.3 A4171.1 A2405.6 A1924.5 AView
→
2500 kVA6940.0 A6014.1 A5213.9 A3007.0 A2405.6 AView
→

Conductor Sizing Guide for Oil-Filled Transformers

Proper conductor sizing is critical for safety and code compliance. Use this guide based on copper conductors with
75°C insulation per NEC Table 310.16.

Current RangeCopper ConductorTypical Application
0-20 A#12 AWGSmall branch circuits
21-30 A#10 AWGStandard branch circuits
31-50 A#8 – #6 AWGSub-panels, small equipment
51-100 A#4 – #1 AWGService entrance, panels
101-150 A1/0 – 2/0 AWGMain service, feeders
151-200 A3/0 – 4/0 AWGLarge feeders
201-300 A250-350 MCMCommercial service
301-500 A400-750 MCMIndustrial feeders
500+ AParallel conductorsLarge industrial, substations
⚠️ Important: For oil-filled transformers, ensure conductor insulation is rated for oil exposure at
cable terminations. Use appropriate weatherhead and bushings for outdoor installations.

FLA Calculation Examples

Example 1: Single-Phase 75 kVA at 240V

FLA = (75 × 1000) ÷ 240 = 312.5 Amps
Recommended conductor: 350 MCM copper

Example 2: Three-Phase 500 kVA at 480V

FLA = (500 × 1000) ÷ (480 × 1.732) = 601.4 Amps
Recommended conductor: Parallel 350 MCM copper

Example 3: Three-Phase 1000 kVA at 600V (Canadian)

FLA = (1000 × 1000) ÷ (600 × 1.732) = 962.3 Amps
Recommended: Parallel 500 MCM copper

Frequently Asked Questions

What is Full Load Amps (FLA)?

FLA is the current drawn by a transformer when it is delivering its rated kVA at its rated secondary voltage. It
represents the maximum continuous current the secondary conductors must carry.

Can oil-filled transformers handle overloads?

Yes, oil-filled transformers have excellent overload capability due to the thermal mass of the oil. Per IEEE C57.91,
they can typically handle 150% load for 30 minutes or 120% for 2 hours without
damage.

Why include 600V in the chart?

600V is the standard commercial/industrial voltage in Canada. Many oil-filled transformers are
specified with 600V secondary for Canadian applications.

Related Resources

📊 More Reference Charts:

Standards & References

Disclaimer: FLA values are calculated at nameplate voltage. Actual current may vary based on voltage regulation
and load power factor. Wire sizing recommendations are guidelines only – always follow NEC/CEC requirements and
consult with a licensed electrical engineer. Last updated: January 2026

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