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📱 EPISODE — Article 326

Integrated Gas Spacer Cable: Type IGS

SLIDE 1 — What Is IGS Cable?
🔋 A SPECIALIZED UNDERGROUND CABLE

Type IGS cable is unique: solid aluminum rod conductors (minimum 250 kcmil) insulated with continuous dry kraft paper, installed inside a medium-density polyethylene conduit (essentially gas pipe), then pressurized with sulfur hexafluoride (SF6) gas at roughly 20 psi.

Why gas? SF6 enhances the insulation and lets the cable handle higher rated voltages than a standard direct-burial cable. This is heavy-duty utility/industrial territory, not something you'll see in a typical residential job.

SLIDE 2 — Where It's Used (and NOT Used)
✅ USES PERMITTED (326.10)
Underground use ONLY, including direct burial, as:
1️⃣ Service-entrance conductors
2️⃣ Feeder or branch-circuit conductors
3️⃣ Underground service conductors

🚫 USES NOT PERMITTED (326.12)
❌ Interior wiring
❌ Exposed in contact with buildings

This cable stays in the ground — it's not coming up into a structure as exposed wiring.

SLIDE 3 — Bending Rules & Fittings
📐 BENDING RADIUS (326.24)

Minimum bend radii scale with conduit size:
🔹 2 in. conduit → 24 in. min radius
🔹 3 in. conduit → 35 in. min radius
🔹 4 in. conduit → 45 in. min radius

🔄 BENDS PER RUN (326.26)
A run between pull boxes/terminations can't exceed the equivalent of 4 quarter bends (360° total) — including bends right at the pull box or termination.

🔧 FITTINGS (326.40)
Terminations/splices must be identified as suitable for MAINTAINING GAS PRESSURE in the conduit. Each length of cable/conduit needs a valve and cap to check pressure or inject gas — this is a pressurized system, so fittings have to hold that pressure reliably.

SLIDE 4 — Construction Specs, Ampacity + Exam Question
🏗️ QUICK CONSTRUCTION SPECS

🔹 Conductors: solid aluminum rods, 1 to 19 rods at ½ in. diameter each, 250 kcmil min – 4750 kcmil max
🔹 Insulation: dry kraft paper tape + pressurized SF6 gas at 138 kPa (20 psi) nominal
🔹 Conduit: medium-density polyethylene, natural-gas-rated pipe, in 2/3/4 in. trade sizes only
🔹 Marking: per 310.8(A), 310.8(B)(1), and 310.8(D)

📊 Ampacity is capped per Table 326.80 — e.g., 250 kcmil = 119A, all the way up to 4750 kcmil = 519A. Always check the table; don't assume standard conductor ampacity tables apply here.

🧠 TEST YOURSELF

Q: Per 326.26, what is the maximum number of quarter bends permitted in a single run of Type IGS cable between pull boxes or terminations?

A) Two quarter bends (180°)
B) Three quarter bends (270°)
C) Four quarter bends (360°)
D) Six quarter bends (540°)

(Drop your answer 👇)

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