Quick Hits

EPISODE 13 — Ampacity Baseline Conditions: In Air vs. Underground/Direct Buried — Article 315 FINALE (315.60(E)–(F))

Slide 1 — Hook "Final episode of Article 315! Wrapping up with the baseline conditions each table family assumes — so you know when the raw table number applies as-is, and when you need to adjust it."

Slide 2 — 315.60(E) In-air tables — baseline conditions

• Tables 315.60(C)(1)-(10) (conductors/cables in air) assume: conductor temperatures of 90°C and 105°C (matching MV-90/MV-105), and a 40°C ambient AIR temperature.

• If your actual ambient differs from 40°C, apply the correction factor from 315.60(D)(4) covered last episode.

Slide 3 — 315.60(F) Underground/direct-buried tables — baseline conditions

• Tables 315.60(C)(11)-(20) (underground ducts and direct burial) assume a longer list of baseline conditions: 20°C ambient EARTH temperature; the specific cable arrangement shown in Figure 315.60(D)(3); a 100% load factor (full, continuous loading — no diversity assumed); a thermal resistance (Rho) of 90; conductor temperatures of 90°C/105°C; minimum burial depths per 305.15; and a maximum depth of 30" to the top of duct banks (or 36" to the top of direct-buried cables) — UNLESS you apply the 315.60(D)(2) derating factor for going deeper than that.

Slide 4 — Quiz + CTA Q: "The underground/direct-buried ampacity tables in 315.60(C)(11)-(20) assume what ambient EARTH temperature baseline?" A) 10°C B) 20°C C) 30°C D) 40°C

✅ Answer: B — 315.60(F)(1): 20°C (68°F) baseline ambient earth temperature.

CTA: 🎉 That's a wrap on ALL of Article 315 — Medium Voltage Conductors, Cable, Cable Joints, and Cable Terminations! Follow for more daily quick-hit study notes as we move into the cable-type articles next, starting with Article 320 (Armored Cable: Type AC).

← View Chapter 3 Home

← Back To Article 315 Home

← Back To Quick Hits Home