The Use Case

A commercial bakery operates mixers, dough sheeters, and ovens that require 460 V three‑phase power. The facility only has a 230/240 V single‑phase service. Because the bakery needs reliable automatic start (no manual high‑leg switching), they are looking at a rotary phase converter with an auto‑start feature to simplify operation.

What Usually Matters for Sizing

  1. HP and voltage – 25 HP motor rated for 460 V three‑phase.
  2. Auto‑start requirement – Converter must include a built‑in high‑leg switch or auto‑transfer that energizes the generated leg automatically when load is applied.
  3. Input capacity – Single‑phase source amperage; a 25 HP load typically draws ~100 A at 240 V during start, so a dedicated 200 A service is advisable.
  4. Transformer need – If only 230/240 V single‑phase is present, a step‑up transformer (e.g., 30–40 kVA) will raise the voltage to 460 V before it reaches the converter’s idler motor.
  5. Converter model – The Phoenix GP50NL is the recommended unit for 25 HP auto‑start applications, offering a larger idler and integrated auto‑start circuitry.

Common Mistakes to Avoid

  • Choosing a non‑auto start converter – Manual high‑leg switching can cause downtime and safety concerns in a bakery environment.
  • Neglecting transformer sizing – An undersized transformer will limit voltage on the generated leg, causing motor overheating.
  • Overlooking continuous duty – Bakery equipment often runs for long cycles; ensure the converter’s thermal rating matches continuous operation.
  • Assuming 460 V can be derived directly from 240 V – Without a transformer, the idler will be under‑volted and unable to sustain full motor torque.

Practical Phoenix Recommendation

From call evidence (E074) we see a bakery customer with a 25 HP auto‑start requirement. The Phoenix GP50NL paired with a 460 V step‑up transformer (≈35 kVA) meets both the power and automatic start needs.

  • Input side – Connect to a dedicated 240 V, 200 A single‑phase circuit protected by a two‑pole breaker sized for the converter’s input current (~90 A).
  • Transformer – A 460 V, 35 kVA transformer will provide roughly 70 A three‑phase output, sufficient for a 25 HP motor (≈55 A FLA).
  • Auto‑start wiring – Use the GP50NL’s built‑in auto‑start relay; no external high‑leg switch is required.

Confirm final sizing against the equipment nameplate: HP, voltage, FLA/LRA, and whether the load runs continuously or intermittently.

What to Have Ready Before Calling

  • Nameplate data for each bakery machine (HP, 460 V rating, FLA, LRA).
  • Single‑phase service details: voltage, breaker size, available amperage.
  • Desired automatic start behavior (e.g., “run when power is applied”).
  • Space and ventilation requirements for the converter and transformer enclosure.
  • Any existing transformer specs if you already own one.