Checklist: what to review before hiring an electrical installation

Before hiring an electrical installation, three things are worth verifying: that the contractor works to NOM-001-SEDE-2012 (Mexico’s national electrical installation standard), that they deliver technical documentation (load calculations, drawings, material specifications), and that they stand behind the work with a written warranty. A badly executed electrical installation is not a cosmetic defect: it is a fire and accident risk that will live hidden in walls and panels for decades.

What signs point to an out-of-code installation?

Many defects can be spotted with the naked eye, without opening a single wall:

• Outlets, plugs or switches that get hot or show burn marks.
• Thermal-magnetic breakers that trip often, or worse, that were swapped for higher-capacity ones “so they stop tripping.”
• Two-slot outlets with no ground terminal, or with the ground terminal present but not connected.
• Exposed cables with no raceway (no conduit or duct), stapled to walls or laid across drop ceilings.
• Splices wrapped only in electrical tape inside overstuffed boxes, or outside any box.
• A panel with no circuit directory, with uncovered empty slots, or with wires of different gauges under a single breaker.
• No ground-fault protection (GFCI devices) in bathrooms, kitchens, outdoor and wet areas, where the standard requires it.
• Lights flickering when equipment starts up, a sign of undersized conductors or loose connections.

None of these signs is cosmetic. Each one shows that whoever did the work either did not know the standard or chose to ignore it, and what is visible is usually the least serious part of what sits inside the walls.

What is NOM-001-SEDE-2012, and what should you demand about it?

NOM-001-SEDE-2012 (Electrical Installations, utilization) is the Mexican official standard that sets the safety specifications electrical installations in the country must meet: conductor and protection selection, grounding systems, raceways, requirements by occupancy type, among many other topics. It is the document against which a verification unit judges whether an installation is safe.

What you should demand is simple: that the proposal state explicitly that design and execution will follow this standard, and that materials carry current certification (look for products certified by accredited bodies, such as ANCE, Mexico’s electrical product certification association). A contractor who cannot hold a basic conversation about the standard that governs the trade should not be wiring your building. In our electrical installations service, compliance with NOM-001-SEDE-2012 is part of the standard scope, not an extra.

What documents should the contractor deliver before you sign?

For a new build, expansion or remodel with load changes, ask for:

1. An itemized quote: scope by line item, brands and models of materials, conductor gauges, labor separated from materials.
2. Load calculations: the document where the building’s loads are computed and the selection of conductors, protections and panel is justified. Without load calculations, the wire gauges are a guess.
3. Drawings or diagrams: circuit layout, location of the panel, outlets and light fixtures. It is also what will let you maintain the installation in the future.
4. A written warranty, with a defined term and scope.
5. Verifiable references from jobs similar in size and type.

For minor work (adding circuits, fixing a panel) the package shrinks, but the itemized quote and the written warranty are never negotiable.

What should a serious electrical quote include?

Beyond the breakdown, a serious quote defines the scope precisely: what it includes (raceways, chasing and patching, grounding, testing) and what it does not (permits, dictamen, major civil work). It specifies brands and gauges instead of phrases like “top-quality material.” It sets an execution timeline and reasonable payment terms, with a down payment proportional to the materials to buy and never the full amount up front. And it covers testing of the finished installation, such as measuring ground system resistance and verifying the protective devices.

What are the red flags in a quote?

• A price notably below the rest: it almost always comes from uncertified material, undersized gauges, or a trimmed scope that later comes back as extras.
• No brands or gauges specified: impossible to compare and impossible to claim against.
• “No load calculations needed”: for any job with new loads, they are needed.
• A quote without a prior site visit: nobody can seriously size what they have not seen.
• A warranty given only verbally, or so conditioned it cannot be enforced.
• Full or majority payment up front.
• Refusal to discuss verification or the NOM: whoever complies with the standard does not fear the topic.
• No tax registration or verifiable address: if something goes wrong, there will be nobody to find.

One flag warrants questions. Two or more, another provider.

When is a dictamen from a UVIE required?

Unidades de Verificación de Instalaciones Eléctricas (UVIE) are accredited bodies that inspect an installation against NOM-001-SEDE-2012 and issue a dictamen, an official compliance report. That dictamen is required, among other cases, for public assembly venues (schools, movie theaters, event halls, large retail) and for higher-capacity installations, typically industrial and commercial; in those cases CFE, the state utility, asks for it as a condition to contract or modify service. The exact thresholds and cases are best confirmed for each project with the UVIE or with your contractor.

What matters when hiring: if your project will need a dictamen, say so from the quote onward. Fixing a finished installation so it passes verification costs far more than building it right the first time, because it means opening up what was already closed.

What warranties should you demand in writing?

Two, and they are different. The equipment and materials warranty comes from the manufacturer, typically 1 to 5 years depending on the product. The labor warranty comes from the installer and covers execution defects: loose connections, bad splices, deficient raceways. This second one is what sets contractors apart: in the market it is usually short or nonexistent, which is why at Tegu labor carries a 10-year warranty.

Demand both in writing, with term, scope and a claims procedure. “Just call me if anything comes up” is not a warranty.

Is it worth doing electrical work yourself?

Swapping a light fixture or a switch, with the circuit de-energized and verified, is within reach of a careful person. Everything else is not: adding circuits, modifying panels, calculating loads or installing grounding demands knowledge of the standard and carries direct safety consequences. The real cost of the “savings” shows up years later as a failure, a fire, or an installation that fails verification when the property is sold or rented. Electricity is one of the few trades where the mistake gives no warning: it seems to work fine until the day it does not.

How often should an existing installation be reviewed?

A professional review every 5 years is a reasonable reference for buildings in normal use, and more often in demanding environments (humidity, dust, industrial loads). An immediate review is warranted by: buying a used property, any of the signs described above, adding significant loads (air conditioners, machinery, electric vehicle chargers), and installations over 20 years old with no intervention. If you have questions about a specific case, our frequently asked questions page covers the most common ones.

Field notes