Quick Hits

EPISODE 12 — Supporting Conductors in Vertical Raceways over 1kva & Induced Currents (305.29, 305.30)

Slide 1 — Hook "Today: vertical raceway support spacing (notice the aluminum/copper columns are FLIPPED compared to Article 300's table!) and avoiding induced-current heating."

Slide 2 — 305.29 Vertical raceway support

• Conductors in vertical raceways need support once the rise exceeds Table 305.29(A)'s values — support at (or near) the TOP of the run, plus intermediate supports as needed.

• Interesting quirk to flag: Table 305.29(A) lists ALUMINUM/copper-clad aluminum FIRST and copper SECOND (opposite of Article 300's table layout) — same general pattern of aluminum getting roughly double the max spacing distance compared to copper at each size band (e.g., 6 AWG-1/0 AWG: aluminum 200 ft max vs. copper 100 ft max).

• Support methods: same four options as Article 300 — insulating wedge clamping devices, inserted boxes with insulating supports, 90°-deflection junction-box routing (cables at intervals no more than 20% of the table spacing), or other approved means. Fire-resistive cable/conductor systems follow their own listing restrictions but never exceed the table values.

Slide 3 — 305.30 Induced currents in ferrous metal

• (A) UNSHIELDED conductors specifically (note the qualifier — Article 300's equivalent doesn't specify "unshielded"): AC conductors in ferrous metal enclosures/raceways need all phase conductors (plus grounded conductor/EGCs, where used) GROUPED together to avoid inductive heating.

• (B) A single unshielded AC conductor through ferrous metal: minimize induction by cutting slots between individual conductor holes, or passing all circuit conductors through one large insulating-walled opening. Aluminum isn't magnetic, so induced currents exist but aren't significant enough to require special treatment.

Slide 4 — Quiz + CTA Q: "Table 305.29(A)'s induced-current grouping rule in 305.30(A) specifically applies to which type of conductors?" A) Shielded conductors only B) Unshielded conductors C) Only conductors over 4/0 AWG D) Only conductors in nonmetallic raceways

✅ Answer: B — 305.30(A) specifically addresses UNSHIELDED conductors grouped in ferrous metal enclosures/raceways.

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