The Use Case

A lift‑station at an apartment complex houses two three‑phase pumps (each rated 5 HP). The site only has 120/240 V single‑phase service. The owner plans to step the voltage up to 480 V after conversion, so both pumps can run on a common three‑phase bus. They need guidance on converter size and whether a transformer is required.

What Usually Matters for Sizing

  1. Total motor horsepower – Two 5 HP pumps = 10 HP total. Phoenix guidelines recommend a converter rated at ≈2 × total HP, so a 20 HP unit provides adequate start‑up torque and voltage regulation.
  2. Voltage conversion – The source is 240 V single‑phase, but the pump bus will be 480 V three‑phase. A step‑up transformer (e.g., 240 V → 480 V) must be paired with the converter; the transformer’s kVA rating should match or exceed the converter’s output power (≈15 kVA for a 20 HP unit).
  3. LRA/FLA of each pump – Pump motors have relatively high LRA, often 2–3 × FLA. Sum the LRA values to ensure the converter‑plus‑transformer can sustain the surge without excessive voltage dip.
  4. Starting sequence – The pumps are not intended to run simultaneously; however, the converter must still handle the worst‑case scenario of both starting together (briefly).
  5. Service capacity and grounding – Verify that the main panel can accommodate the additional input current for the converter (≈30 A at 240 V) and that the transformer is properly grounded per NEC.

Common Mistakes to Avoid

  • Skipping the transformer step – Trying to run a 480 V pump directly from a 230 V converter will damage equipment.
  • Undersizing the transformer – A transformer rated too low will overheat during start‑up, causing voltage collapse on the pump bus.
  • Using a bare NL/PL unit – For pumps with high starting currents, a standard “NL” (non‑linked) converter may not provide enough phase balance; an AutoLink or compressor‑duty model is preferable.
  • Neglecting total kVA – The combined kVA of converter plus transformer must be greater than the summed motor load to avoid overload.

Practical Phoenix Recommendation

The call record (E035) suggests the GP10NLTA package: a 10 HP “Phase‑Only” rotary converter paired with a transformer‑ready enclosure. However, because the total load is 10 HP and voltage must be stepped up to 480 V, we recommend moving to the next size – a 20 HP GP20PO (or GP20PLA if you prefer AutoLink) together with a 240 V → 480 V, 25 kVA transformer. This combination satisfies:

  • Adequate start‑up torque for both pumps.
  • Proper voltage transformation to the required 480 V bus.
  • Sufficient kVA margin (20 HP ≈ 15 kW; 25 kVA transformer provides headroom).

Final sizing must be confirmed against each pump’s nameplate (HP, LRA/FLA), the transformer’s voltage ratio, and the building’s service capacity.

What to Have Ready Before Calling

  1. Pump nameplates – HP, voltage, LRA, FLA for both units.
  2. Desired operating voltage – Confirmation that 480 V three‑phase is required.
  3. Existing single‑phase service details – Main breaker size, available conduit space, and distance to the lift station.
  4. Transformer preferences – Whether you need a pre‑wired enclosure or separate transformer; typical kVA rating (25 kVA recommended).
  5. Any future expansion plans (additional pumps or loads) that might affect converter/transformer sizing.

Providing these specifics will let Phoenix engineers confirm the 20 HP GP20PO + 25 kVA transformer solution is optimal and generate a precise quote quickly.