Reading a network transformer datasheet has a learning curve. Here's a structured approach to extracting what your design actually needs.
Step 1 — Identify the Application Standard
Compliance statement to look for in the datasheet:
"Meets IEEE 802.3 Clause 40" → 10/100BASE-TX
"Meets IEEE 802.3 Clause 40/25/28" → 1000BASE-T (Gigabit)
"IEEE 802.3at PoE rated" → Power over Ethernet
"IEC 60601-1 5000V isolation" → Medical grade

If no IEEE 802.3 clause is cited → ask the supplier or find a different part
Step 2 — Decode the Electrical Specifications Table
ParameterSymbol10/100BASE-TX1000BASE-TTest ConditionOpen Circuit InductanceOCL≥ 350µH (min)≥ 1000µH (min)100kHz, 0.1V RMSInsertion LossIL< 1.0 dB (max)< 1.0 dB (max)1–100MHz, 100Ω diffReturn LossRL> 16 dB (min)> 16 dB (min)1–100MHz, 100Ω diffIsolation VoltageV_ISO≥ 1500V AC≥ 1500V AC1 min, 50/60HzTurns Ratio—1CT:1CT1CT:1CT—DC ResistanceDCR< 5Ω typ< 3Ω typPer winding
Step 3 — Read Test Conditions, Not Just Values
python# OCL test condition matters

Different conditions = different (incomparable) values

def compare_ocl_valid(spec_a, spec_b):
"""
Returns True only if both specs use the same test conditions
"""
standard_cond = {"freq_kHz": 100, "voltage_rms": 0.1}

a_valid = (spec_a["test_freq_kHz"] == standard_cond["freq_kHz"] and

           spec_a["test_voltage_rms"] == standard_cond["voltage_rms"])

b_valid = (spec_b["test_freq_kHz"] == standard_cond["freq_kHz"] and

           spec_b["test_voltage_rms"] == standard_cond["voltage_rms"])

if not (a_valid and b_valid):

    print("⚠️ Test conditions differ — values not directly comparable")

    return False

return True

Real world trap:

spec_non_standard = {"ocl_uH": 600, "test_freq_kHz": 10, "test_voltage_rms": 1.0}
spec_standard = {"ocl_uH": 380, "test_freq_kHz": 100, "test_voltage_rms": 0.1}

Same physical part — different measurement condition

600µH at 10kHz/1V ≠ 600µH at 100kHz/0.1V

Step 4 — Design to Min/Max, Not Typical
WRONG approach:
Datasheet shows OCL typ = 480µH
Design assumes 480µH is the production value ✗

CORRECT approach:
Datasheet shows OCL min = 350µH, typ = 480µH
Design must work at 350µH ✓
Simulate and verify at the min column value

Same rule applies to insertion loss:
Datasheet shows IL typ = 0.4 dB, max = 1.0 dB
Design for 1.0 dB worst case, not 0.4 dB typical
Pin-Out: The Most Common Error Source
Pin compatibility ≠ package compatibility

Two 8-pin SMD network transformers from different vendors:
Vendor A: Pin 1=TX+, Pin 2=TX−, Pin 3=CTx, Pin 4=RX+...
Vendor B: Pin 1=RX+, Pin 2=RX−, Pin 3=CTx, Pin 4=TX+...

Building footprint from Vendor A's datasheet for Vendor B's part = crossed TX/RX
Result: link never establishes, no obvious error in schematic

Always build footprint from the specific part's datasheet pin-out.
Never reuse footprints across different vendor parts.
Isolation Voltage: Check the Test Duration
Standard production test: 1500V AC for 60 seconds
Acceptable shorthand: "hipot tested at 1500V AC"

Red flag: "1500V AC momentary" or no duration stated
→ Much lower accumulated stress on insulation
→ May pass initial test but fail in service under sustained stress

For industrial (factory floor, outdoor) applications:
→ Specify 2500V AC, 60 seconds minimum
→ Ask supplier for production test report
Datasheet Checklist
[ ] IEEE 802.3 clause stated (Clause 40 / 25 / 28)
[ ] OCL tested at 100kHz, 0.1V RMS
[ ] OCL value is Min column, not Typ
[ ] IL and RL specified over 1–100MHz with 100Ω differential
[ ] Isolation voltage test duration documented
[ ] Turns ratio is 1CT:1CT (center taps confirmed)
[ ] Pin-out diagram matches your PCB footprint (verify every pin)
[ ] Operating temperature range covers your application
[ ] PoE rated if DC bias is present (PSE or PD designs)
Source
Voohu Technology (www.voohuele.com) — network transformers with complete datasheets: OCL at 100kHz/0.1V RMS, temperature-characterized specs, application circuits included. MOQ 50pcs, DHL 3–5 days.