October 08, 2026

Poor power quality is scrapping your parts

A spindle finishes a bore twelve microns out of tolerance. The operator logs it as tool wear, changes the insert, and runs the next part. Nobody checks the incoming voltage, because nothing on the floor suggested there was anything to check. The lights did not flicker. The CFE bill looked normal.

Power quality failures do not announce themselves in a precision shop. They announce themselves in the scrap bin six weeks later, as a rejection rate that crept from 1.2% to 2.1% and never came back down. The plant files it under tooling or under machine condition, because those are the two categories the quality system knows. Voltage sags, harmonic distortion, and a power factor drifting under load sit in a third category that appears on no CFE invoice and in almost no root cause analysis.

The regulator has now made that third category harder to ignore. Mexico’s Código de Red tightened its power factor requirement from a 0.95 to 1.0 band to a 0.97 to 1.0 band. The new floor has applied since April 2026, measured in five-minute intervals across at least 95% of each monthly period, under the Código de Red the CRE issued in resolution RES/550/2021. The requirement applies to every high-voltage connected facility and every medium-voltage facility with contracted demand of 1 MW or more. That covers the precision machining plants feeding Mexico’s automotive and aerospace supply base almost without exception. Oversight now sits with the Comisión Nacional de Energía (CNE), which replaced the Comisión Reguladora de Energía in March 2025 and operates under the Secretaría de Energía. Serious non-compliance with the grid’s quality, reliability, continuity, and security rules carries a fine of 10% of the prior year’s gross income under article 184 of the Ley del Sector Eléctrico, which replaced the Ley de la Industria Eléctrica.

Power factor is the symptom the tariff happens to price. Harmonic distortion and voltage sags are two more. Neither one shows up as a line item on a CFE bill. They show up as tool chatter, spindle speed variation, and out-of-tolerance parts that get scrapped, reworked, or shipped and then rejected by a customer running incoming inspection against an aerospace or automotive print. A plant that tightens its power factor to meet the April 2026 threshold and stops there has fixed the number CFE checks. The number its own quality department should be checking goes untouched.

What the new standard requires

The mechanics of the new threshold matter for a precision shop specifically. CNC equipment, servo drives, and variable-frequency spindle controls are exactly the load profile that makes power factor hardest to hold. They are non-linear switching loads. They are also the loads most sensitive to the power quality problems the tightened Código de Red now polices. A shop that has not run a Class A power quality analyzer against its own bus in the past year does not know where it sits against the new 0.97 threshold. The penalty is income-based, not a flat fee, so the cost of finding out late scales with the size of the operation that waited.

The Código de Red limits how much current harmonic distortion an industrial user can inject into the grid at its connection point. High harmonic distortion can overheat transformers and trip protection systems. That is the grid-facing consequence. The equipment-facing consequence runs the other direction, and compliance guidance discusses it less because it never lands on a CFE invoice. A distorted or sagging supply voltage degrades the same servo and spindle systems a precision shop depends on to hold tolerance. Plants budgeting for Código de Red compliance purely to avoid a fine are underpricing the value of the fix.

How a voltage sag ruins a part

A 2013 doctoral thesis at the Universidad Autónoma de Querétaro measured this mechanism on a retrofitted CNC lathe, and the physics has not changed since. The research found that low-voltage sags, which earlier studies identify as the most common electrical disturbance, produced measurable variation in spindle motor speed, tool holder vibration across all three axes, torque output, and finished surface roughness during active machining cycles. Its experiments sampled at 6,000 and 12,000 Hz to capture those disturbances in real time. That rate is the point. A voltage event moves fast against a machining cycle running at a fixed feed rate and spindle speed. A sag lasting a fraction of a second shifts torque and vibration mid-cut. On a part machined to aerospace or automotive tolerance, that shift decides whether the part passes inspection.

An outage is easier to catch. It stops the machine, and the operator knows immediately that something happened. A sag or a harmonic distortion event can pass through a machining cycle without tripping anything. The part looks finished and sits out of tolerance, and only a coordinate measuring machine will say so. Sometimes nobody says so until the customer’s incoming inspection, after the part has already shipped. Tight tolerances in aerospace CNC machining start around ±0.025 millimeter, and precision bores can be held to ±0.012 millimeter, with geometric requirements on roundness, concentricity, and positional accuracy layered on top. That reference comes from published engineering guidance on machining tolerances. A voltage disturbance measured in milliseconds is enough to push a cut outside that band. Nobody on the floor knows it happened until the part fails inspection.

If nobody has cross-referenced your out-of-tolerance parts against a voltage disturbance log, those rejections are still being charged to tooling. Talk to an advisor.

Why Querétaro is most exposed

Querétaro’s aerospace cluster concentrates more than 80 companies, including named tenants Safran, Airbus, and Bombardier. Mexico’s aerospace sector overall supports about 60,000 direct jobs, according to Querétaro’s Secretaría de Desarrollo Sustentable and the Secretaría de Economía. The region’s manufacturing focus is engine and turbine component fabrication, advanced structural engineering, and composite materials. That work sits at the highest-tolerance end of precision machining in the country. The same grid feeding those plants is the grid where a power quality event carries the most expensive downside per incident. The concentration of sensitive, non-linear industrial load there is high enough to matter to grid stability at a system level, well beyond an individual plant’s bill.

The grid conditions behind more frequent power quality events are national. Electricity demand grew 3.4% and 3.5% in 2022 and 2023 while transmission infrastructure grew a fraction of a percent in the same years. The source is the Mexican Institute for Competitiveness. A grid running closer to its limits produces more voltage sags and harmonic events as a matter of physics, and not only more outright outages. A precision shop that has gone years without a full-plant power quality event should not read that as evidence the risk has passed. Read it as evidence the risk has not yet found the vulnerable equipment on that specific line.

What the data can’t prove

Nobody publishes a per-part scrap cost for Mexican precision shops. The number moves too much to average. It turns on part complexity, material, and how far into the cycle the defect is caught. An early-stage aluminum bracket runs a few hundred dollars. A late-stage titanium or nickel-superalloy engine component with dozens of machining hours already invested runs to tens of thousands. Your own scrap and rework log carries the figure for your part families. That is the number to build the capital case on.

Not every precision shop needs to treat this as urgent. A plant machining lower-tolerance automotive components on well-established, mature processes with generous tolerance bands has less exposure than an aerospace supplier working at the tightest end of the range. The capital case for power quality correction should scale with tolerance sensitivity, and not apply uniformly across every CNC operation regardless of what it produces.

How to protect the process

Run a Class A power quality audit before your next Código de Red compliance check. Do not schedule it as a separate project afterward. The same instrumentation that verifies your power factor against the new 0.97 threshold captures harmonic distortion and voltage sag data. A compliance-only audit leaves that on the table. Doing both together costs less than running them separately.

Correlate your scrap and rework log against your power quality data by timestamp. If your quality system already flags out-of-tolerance parts, cross-reference those events against any recorded voltage disturbance in the same window. That is the fastest way to find out whether your plant already has a documented pattern connecting grid events to scrapped parts. It beats guessing at the exposure.

Prioritize power conditioning on the equipment machining your tightest-tolerance, highest-value parts first. A plant with a mix of automotive and aerospace work should not spend its power quality budget uniformly across every machine. Protect the spindles and servo drives cutting the parts where an out-of-tolerance result is most expensive to discover late.

Build the compliance requirement and the quality case into one budget request. The tightened power factor threshold, in force since April 2026, gives finance a hard compliance requirement to act against. Pair that request with the scrap-reduction case, backed by your own correlated data. It is a stronger capital argument than either one submitted alone.

Power quality and grid code risk review

Mexico Energy Partners measures where your plant sits against the 0.97 power factor floor in force since April 2026, then correlates recorded voltage sags and harmonic events against your own scrap and rework log. Facility location, operating schedule, approximate demand, and a short description of the current concern are enough to start, and no CFE bill is required. CFE bills, the single-line diagram, and the scrap log come after the first conversation, under NDA.

Talk to a Mexico Energy Partners advisor or email info@mexicoenergypartners.com. Mexico Energy Partners sells no equipment and is compensated only by the client.

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