Will a Phase Converter Affect My Utility Bill?
Yes — but less than you might think, and it is easy to calculate.
Two Things That Add to Your Bill
1. Conversion Losses (~10–15%)
A rotary phase converter is approximately 85–90% efficient. If your three-phase equipment draws 10 kW, your single-phase input will be approximately 11–12 kW. That 1–2 kW difference is the conversion loss — it shows up as heat in the idler motor. At $0.12/kWh running 8 hours/day, that is about $0.96–$1.92/day in extra cost. For most shops: under $50/month.
2. Idler Motor No-Load Draw
When your equipment is off but the converter is still powered, the idler motor draws a small no-load current — typically 2–5% of rated HP. A 20 HP idler running 10 hours/day at $0.12/kWh costs roughly $2–$5/week in no-load draw. Turn the converter off when not in use to eliminate this.
Compared to the Alternative
Running utility three-phase to your building costs $10,000–$50,000+ in most rural or suburban areas. A phase converter pays for itself in utility extension cost savings alone — the slight efficiency loss is negligible by comparison.
Summary
Expect a modest increase in your utility bill — typically 10–20% more power draw versus direct three-phase utility for the same equipment. For most shops, this is $20–$80/month depending on usage.
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Utility Bill — FAQ
Should I turn the converter off at night?
Yes — when the shop is closed, turning the converter off eliminates the idler motor no-load draw (2–5% of rated HP). NL Series converters start in 2–3 seconds so there is no warmup penalty for cycling power daily.
Does a larger converter cost more to run than a smaller one?
The no-load idler draw scales with converter HP — a 40 HP idler draws more no-load current than a 10 HP idler. Under load, power draw is determined by equipment demand, not converter size.
Is there a demand charge impact?
High-HP converter startups draw inrush current that can create a brief demand spike. For very large converters (50+ HP), consult your utility about demand charge implications.
Related Articles
- How to Size a Rotary Phase Converter
- What Is a Rotary Phase Converter?
- Rotary vs Digital Phase Converters
- Phase Converter FAQ
Questions? Talk to an engineer.
Free sizing help. Made in Phoenix, AZ. Lifetime warranty on every unit.
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