Transformer Full Load Amps Chart: Complete FLA Reference - Power Transformer Technical Guide & Educational Resources

Quick reference tables for transformer full load current at all standard voltages, plus formulas and wire sizing
recommendations

Full Load Amps Formulas

Single-Phase:
FLA = (kVA × 1000) ÷ Voltage Three-Phase:
FLA = (kVA × 1000) ÷ (V × 1.732)

The full load amps (FLA) of a transformer is the maximum current the transformer can deliver at its
rated kVA and voltage without exceeding its thermal limits. This chart provides quick reference values for sizing
conductors, overcurrent protection, and system design.

Single-Phase Transformer FLA Chart
Three-Phase Transformer FLA Chart
Wire Sizing Guide
Calculation Examples
FAQ

Single-Phase Transformer Full Load Amps Chart

Full load current for single-phase transformers at standard voltages:

kVA	120V	208V	240V	277V	480V	600V
3	25.0	14.4	12.5	10.8	6.2	5.0
5	41.7	24.0	20.8	18.1	10.4	8.3
7.5	62.5	36.1	31.2	27.1	15.6	12.5
10	83.3	48.1	41.7	36.1	20.8	16.7
15	125.0	72.1	62.5	54.2	31.2	25.0
25	208.3	120.2	104.2	90.3	52.1	41.7
37.5	312.5	180.3	156.2	135.4	78.1	62.5
50	416.7	240.4	208.3	180.5	104.2	83.3
75	625.0	360.6	312.5	270.8	156.2	125.0
100	833.3	480.8	416.7	361.0	208.3	166.7
167	1391.7	803.0	695.8	602.9	347.9	278.3
250	2083.3	1201.9	1041.7	902.5	520.8	416.7
333	2775.0	1600.9	1387.5	1202.2	693.8	555.0
500	4166.7	2403.8	2083.3	1805.1	1041.7	833.3

📝 Note: Values calculated using formula: FLA = (kVA × 1000) ÷ Voltage. For detailed specifications
of each size, see our Transformer
Sizing Chart.

Three-Phase Transformer Full Load Amps Chart

Full load current for three-phase transformers at standard voltages:

kVA	208V	240V	380V	480V	600V
9	25.0	21.6	13.7	10.8	8.7
15	41.6	36.1	22.8	18.0	14.4
30	83.3	72.2	45.6	36.1	28.9
45	124.9	108.3	68.4	54.1	43.3
75	208.2	180.4	114.0	90.2	72.2
112.5	312.3	270.6	171.0	135.3	108.2
150	416.4	360.8	228.0	180.4	144.3
225	624.6	541.3	342.0	270.6	216.5
300	832.8	721.7	456.0	360.8	288.7
500	1388.0	1202.8	760.0	601.4	481.1
750	2082.0	1804.2	1140.0	902.1	721.7
1000	2776.0	2405.6	1520.0	1202.8	962.3
1500	4164.0	3608.4	2280.0	1804.2	1443.4
2000	5552.0	4811.3	3040.0	2405.6	1924.5
2500	6940.0	6014.1	3800.0	3007.0	2405.6

Formula Used:
FLA = (kVA × 1000) ÷ (Voltage × 1.732)
where 1.732 = √3 (the square root of 3 for three-phase calculations)

Wire Sizing Guide Based on FLA

Recommended minimum wire sizes based on full load amps (copper conductors, 75°C rating per NEC):

Full Load Amps	Minimum Wire Size (AWG/MCM)	Recommended Conduit Size
0-15 A	#14 AWG	1/2″
16-20 A	#12 AWG	1/2″
21-30 A	#10 AWG	1/2″
31-40 A	#8 AWG	3/4″
41-55 A	#6 AWG	3/4″
56-70 A	#4 AWG	1″
71-85 A	#3 AWG	1″
86-100 A	#2 AWG	1-1/4″
101-115 A	#1 AWG	1-1/4″
116-130 A	1/0 AWG	1-1/2″
131-150 A	2/0 AWG	1-1/2″
151-175 A	3/0 AWG	2″
176-200 A	4/0 AWG	2″
201-230 A	250 MCM	2-1/2″
231-255 A	300 MCM	2-1/2″
256-285 A	350 MCM	3″
286-310 A	400 MCM	3″
311-380 A	500 MCM	3-1/2″

Calculation Examples

Example 1: Single-Phase 25 kVA at 480V

Given: 25 kVA single-phase transformer, 480V secondary

Formula: FLA = (kVA × 1000) ÷ Voltage

Calculation: FLA = (25 × 1000) ÷ 480 = 52.1 amps

Wire Size: #6 AWG (rated for 55A)

Example 2: Three-Phase 500 kVA at 480V

Given: 500 kVA three-phase transformer, 480V secondary

Formula: FLA = (kVA × 1000) ÷ (Voltage × 1.732)

Calculation: FLA = (500 × 1000) ÷ (480 × 1.732) = 601.4 amps

Wire Size: Parallel 350 MCM or 500 MCM conductors

Frequently Asked Questions

What is full load amps (FLA) on a transformer?

Full load amps is the maximum current the transformer can continuously deliver at its rated kVA and voltage without
overheating. It’s used for sizing conductors and overcurrent protection.

Why do three-phase transformers have lower FLA than single-phase at the same kVA?

Three-phase power is distributed across three conductors, so each conductor carries less current. The formula
includes the √3 factor to account for this distribution.

How do I calculate FLA for a voltage not shown in the chart?

Use the formulas:
Single-phase: FLA = (kVA × 1000) ÷ Voltage
Three-phase: FLA = (kVA × 1000) ÷ (Voltage × 1.732)

What overcurrent protection should I use?

Per NEC 450.3, transformer primary overcurrent protection should be 125% of rated primary current for transformers 9
kVA and larger. Consult local codes for specific requirements.

Related Resources

Disclaimer: Values calculated using standard electrical formulas. Wire sizing based on NEC Table 310.16 for 75°C
copper conductors. Always consult a licensed electrician and verify with local codes. Last updated: January
2026