When five sugarbushes start at once.

The math

A typical Vermont rural distribution feeder runs at 7,200 volts line-to-neutral, single-phase, with pole-mounted transformers stepping it down to 240/120 V at the customer. The feeder conductors are usually 4/0 ACSR aluminum on poles a few hundred feet apart. The voltage at the customer end is the source voltage minus the IR drop across the line — and on a long rural lateral, that drop is significant.

Now suppose four sugarhouses are tied to the same lateral. Each runs a 7.5 HP three-phase vacuum pump. Across-the-line starting current per pump is approximately 6× the full-load amps, or about 108 A peak inrush. If two pumps start simultaneously (which they will, because every sugarmaker on the road is watching the same temperature gauge and starts at the same time of day), peak inrush on the lateral is 216 A for 8–12 cycles.

At the substation transformer, that inrush is small. At the customer end of a 1,200-foot rural lateral, it sags the local voltage by 18–22%. Equipment downstream sees 188 V instead of 240 V for those 8–12 cycles. Most equipment is fine. Some isn't.

What sags and what doesn't

• Incandescent and halogen lighting: visibly browns. Annoying, harmless.
• LED fixtures: mostly fine. Modern drivers tolerate 18% sag for cycles.
• Refrigeration contactors: drop out at about 70% of nominal. The bulk-tank chiller's contactor is the most common drop-out we hear about; the chiller cycles back on by itself.
• PLC controllers on RO units: brown and reset. Some lose state; some don't. The 2018 Lapierre PLC on the East Craftsbury sugarhouse is a known offender.
• Computers and any UPS-less electronics: may or may not survive. Treat as expendable during the run.
• Heat pumps and AC compressors: drop out and refuse to restart for 3 minutes (compressor protection lockout). Annoying for the dwelling on a frosty late-March night.

Soft-start as the standard answer

A soft-start motor controller ramps the voltage to a three-phase motor over 5 to 30 seconds. Inrush drops from 6× FLA to about 2.2× FLA. On a single 7.5 HP pump, that's the difference between a 108 A spike and a 40 A ramped curve. On a feeder full of sugarhouses, it's the difference between a brownout that drops every chiller in town and a slow, well-mannered start that nobody notices.

We standardized on soft-start for every motor > 5 HP in 2020. The unit cost (roughly $480 for an Eaton SVX or comparable, plus an hour of installation) pays for itself the first time a customer's heat pump doesn't trip its protection lockout during a Saturday afternoon start. We have, since 2020, retrofitted soft-starts on 23 existing vacuum pumps and 14 RO feed pumps. Customer reports of "the lights just dimmed" calls have dropped roughly 70% in the population we serve.

What a sugarmaker can do

1. Specify a soft-start on every new motor over 5 HP. If the rig comes from CDL or Lapierre without one, ask for it; their dealers will install one as a factory option.
2. Add a Type-2 SPD on the equipment sub-panel. Power-quality events and lightning transients use the same path; same device protects against both.
3. Stagger the start of the vacuum and the RO by 60 seconds. Most modern controllers do this automatically; verify yours does.
4. If you're on a small lateral and you know your neighbors' schedules, coordinate. We are not joking. The two times we've sat in on a sugarmakers' association meeting in March, half the agenda was scheduling.
5. Talk to your utility — Green Mountain Power, WEC, or VEC. They can sometimes upsize the lateral transformer if enough sugaring load is on a single pole.

What we noticed in 2026

The 2026 sap run was a hard one — a long, slow start in late February with several false thaws followed by a hard freeze, then a compressed two-week peak in mid-March. The lateral on Stannard Mountain Road was at full load for 11 consecutive afternoons. We did not get a single power-quality complaint call from any of our soft-started customers on that lateral. We got two calls from non-customers on the same lateral. We bid both jobs as J-08 service-call diagnostics; both turned into J-03 retrofits.

Related: J-03 Sugarhouse power and East Craftsbury sugarhouse evaporator wiring (Nov 2025) for the worked example.