The Use Case

A customer already owns an LRA‑127 compressor‑duty phase converter (a prior order) rated at 7.5 HP and wants to ensure it is correctly sized for their current single‑phase supply, or possibly replace/upgrade it. The unit will be used to run typical HVAC/compressor loads such as a small air‑handler or refrigeration system.

What Usually Matters for Sizing

  1. Converter name‑plate – Rated HP (7.5 HP), voltage input range, LRA/FLA of the converter itself, and its compressor‑duty rating.
  2. Load characteristics – The downstream equipment’s horsepower (or kW), voltage, and especially whether it is a compressor/HVAC duty load. These loads have high inrush currents; Phoenix’s AutoLink/compressor‑duty sizing accounts for that.
  3. Input service – Usually 230 V or 240 V single‑phase. Verify that the converter’s input rating matches the available voltage and that the feeder can supply the required amperage (converter input current ≈ HP × 0.75 / V).
  4. Starting behavior – If the downstream compressor starts directly on line, LRA can be several times FLA; AutoLink models include built‑in soft‑start capability to reduce stress.

Common Mistakes to Avoid

  • Treating a compressor‑duty converter as a generic NL unit – The internal circuitry differs (larger capacitors, different overload curves). Using the wrong model can cause premature failure.
  • Overlooking input amperage limits – Even a 7.5 HP unit can draw >30 A on a 230 V single‑phase feeder at start; undersized branch circuits will trip.
  • Skipping verification of existing unit’s condition – Older converters may have degraded capacitors, affecting performance and requiring refurbishment rather than replacement.

Practical Phoenix Recommendation

Based on the call record where an existing GP20NLA (a 20 HP compressor‑duty model) was referenced, Phoenix recommends using the AutoLink/Compressor‑Duty series for any LRA‑127 style application. For a 7.5 HP load, the appropriate model is typically the GP10NLA or its current catalog equivalent (often labeled as a “10 HP compressor‑duty” unit).

If the existing LRA‑127 is still functional and meets the input voltage/amperage constraints, it can continue to be used. However, for reliability and warranty support Phoenix advises confirming that the converter’s name‑plate matches or exceeds the downstream load’s HP × 1.5 factor (a common compressor‑duty safety margin).

Final sizing should always be validated against the actual equipment’s name‑plate data: HP, voltage, LRA/FLA, and any soft‑starter features. If the downstream load operates at a higher voltage than the single‑phase source can provide, a step‑up transformer package may be required before the converter.

What to Have Ready Before Calling

  • Converter name‑plate photo or details – Model (LRA‑127), rated HP (7.5 HP), input voltage range, LRA/FLA.
  • Downstream equipment specs – HP or kW, voltage, LRA, FLA, and whether it is a compressor/HVAC duty load.
  • Single‑phase service information – Voltage (230 V/240 V), breaker size, conductor rating, distance to the converter location.
  • Operational profile – Continuous run vs. intermittent start, any existing soft‑starter or VFD, and whether multiple loads will share the converter.

Providing these items lets Phoenix quickly confirm if the LRA‑127 is still appropriate, recommend an upgraded AutoLink model if needed, and ensure the entire system runs safely on single‑phase power.