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Motor Starter & VFD Selection Tool

NEC Article 430 · Motor FLA · Starting Method · Protection

When to use: Use this tool when specifying a motor controller and its protection. It looks up motor full-load current from NEC Table 430.250 (3-phase) or 430.248 (1-phase), recommends a starting method (DOL, wye-delta, soft starter, or VFD) from the load and inrush constraints, and sizes overload protection (430.32), branch-circuit conductors (430.22), and short-circuit / ground-fault protection (430.52). Per 430.6(A), table FLA — not nameplate — sizes conductors and OCPD; nameplate FLA sizes the overload relay.

Motor & System
optional
SF
Application Constraints
starts/hour
/hr
Table FLA Used (NEC 430.6)
34
A
NEC Table 430.250 (25 HP @ 460V)
⚡ Recommended: VFD
Variable Frequency Drive (VFD)
Variable-torque load (pump) with inrush limitation. A VFD gives the largest energy savings on pump/fan loads (affinity laws), eliminates inrush, and handles frequent starts without thermal stress.
Ratings & Protection
VFD Continuous Rating (≥ FLA)≥ 35 A
Overload Setting (430.32, 125%)42.5 A
Overload Max (430.32(C))47.6 A
Branch Conductor (430.22, 125%)42.5 A min
Inv-Time Breaker (430.52, 250%)→ 90 A
Breaker Max to start (≤400%)125 A
Dual-Elem Fuse (430.52, 175%)→ 60 A
Dual-Elem Fuse Max (≤225%)70 A
Sizing Basis
• FLA from table = 34 A (NEC 430.6 — table value sizes wire & OCPD)
• Overload = 125% × FLA (SF ≥ 1.15 per 430.32)
• Conductor ≥ 125% × FLA = 42.5 A; pick wire from 310.16
• Breaker calc = 250% × FLA = 85 A → 90 A std
• Dual-elem fuse calc = 175% × FLA = 59.5 A → 60 A std
NEC References
NEC 430.6(A) — Use table FLA (not nameplate) for wire/OCPD
NEC Table 430.250 / 430.248 — Motor full-load current
NEC 430.22 — Branch conductor ≥ 125% of FLA
NEC 430.32 — Overload 115% / 125% (max 130% / 140%)
NEC 430.52 — Branch SC & GF protection (250% / 175% / 300%)
NEC 430 Part IX — Disconnecting means
NEC 430 Part X / 110 — Adjustable-speed drive (VFD) input protection