Commercial Standby Generator Requirements: Emergency, Legally Required and Optional Systems

A commercial standby generator can mean very different things depending on the building and the loads it carries. A restaurant that wants its walk-in coolers to survive an outage has a different system from a building whose exit lighting and fire alarm must stay powered by law. The National Electrical Code treats those as different systems with different rules. Knowing which one your building needs is the first step, and it shapes the transfer switches, the wiring, the fuel supply and the testing for years after the job is done.

We sell and install Generac home standby and commercial generators. For the work we do on business properties, see our commercial standby generators page and our commercial electrical services hub.

The three kinds of standby systems in the NEC

The NEC splits backup power into three articles. Each article has its own rules for wiring, transfer equipment, signs and testing, and the stricter the category, the more it asks of the installation.

• Article 700, emergency systems: power for loads that protect life when normal power fails, such as egress lighting, exit signs and certain fire and life safety equipment.
• Article 701, legally required standby systems: power required by a code or a government authority for loads that are not life safety in the same sense, but whose loss could create hazards or hamper rescue or firefighting.
• Article 702, optional standby systems: power the owner chooses to install to protect property or keep the business running, such as refrigeration, computers, heating and cooling, or a whole building.

A building can have more than one of these. A single generator can sometimes supply several categories, but the code requires the emergency loads to be kept separate from the rest, with their own transfer equipment and wiring, so that a fault on an optional load cannot take out an exit light.

Who decides which category applies

The category is not a choice the electrician makes on site. Whether a load must be on an emergency system or a legally required standby system comes from the building and fire codes that apply to the occupancy, and from any other code or authority that requires it. The design professional on the project identifies which loads fall where, and the authority having jurisdiction, which inside San Antonio is the City of San Antonio Development Services Department along with the fire marshal, has the final word.

What the owner decides is everything above that floor. If the code requires nothing, a generator for refrigeration, servers, phones or the whole building is an optional standby system under Article 702. That is the most common kind of commercial standby generator for small and mid sized businesses, and the owner sets what it carries.

Transfer switches and how they are sized

The transfer switch moves the loads from utility power to the generator and back. On a commercial job it is usually an automatic transfer switch, and it has to be rated for the loads it carries and for the fault current available at its location. The equipment is listed for the use, and transfer equipment for emergency systems has its own requirements that do not apply to optional systems.

• Sized for the load it transfers, from the load calculation for those circuits.
• Rated for the available fault current where it is installed.
• Separate transfer equipment for emergency loads, where the building has them.
• Located with the working space in front of it that NEC 110.26 requires.

The same principles apply at home on a smaller scale, which we cover on our transfer switch installation page and in our guide to generator transfer switch types.

Fuel supply

Commercial standby generators run on diesel, natural gas or propane, and the choice has code consequences. Some emergency systems are required to have fuel stored on site for a set run time, which a utility gas line cannot always satisfy on its own. Optional standby systems have no such requirement, so many businesses choose natural gas for its unlimited run time and lack of fuel to rotate.

Whatever the fuel, the supply has to be sized for the generator at full load. A natural gas meter or service that is adequate for the building's heating may not be adequate for a large generator added to it. That is a question for the gas utility and a licensed plumber. Gas line and gas connection are not included in our electrical work. That is a licensed plumber's work and we quote it separately.

The fuel decision is the same one homeowners face at a smaller scale, which we cover in natural gas vs propane standby generators.

Testing and maintenance

Emergency and legally required standby systems have to be tested and maintained on a schedule, with written records the inspector or fire marshal can review. NFPA 110, the standard for emergency and standby power systems, is the one usually applied to the generator itself, and it sets out periodic running tests, load tests and inspection of the batteries, fuel and transfer equipment.

Optional standby systems are not held to that schedule by the code, but an owner who skips maintenance is betting the business on a machine that has not run under load in a long time. Most generators exercise themselves on a schedule, and that exercise is the start of maintenance, not all of it. Oil, filters, batteries and the transfer switch need attention on the schedule in the manufacturer's manual.

Our generator service and repair page covers what that service work looks like, and a maintenance agreement can put it on the calendar with the rest of the building.

Choosing what an optional system carries

For most small and mid sized businesses, the commercial standby generator they are buying is an optional system, and the useful work is deciding what it should carry. A generator sized for the whole building costs more than one sized for the loads that actually stop the business. A short list made with the people who run the place usually gives the answer.

• Refrigeration and freezers, where an outage means lost stock.
• Servers, network equipment, phones and the point of sale.
• Security, access control and cameras.
• Heating and cooling for the spaces that must stay open, or for equipment rooms.
• Lighting for the areas staff need to keep working.

Each of those loads goes on the load calculation that sizes the generator and the transfer switch. Loads left off the list are not a problem as long as everyone knows they will be dark during an outage.

Permits and inspections in San Antonio

A commercial standby generator needs an electrical permit. Inside the city limits it goes through the City of San Antonio Development Services Department, and the work is inspected under the 2023 National Electrical Code the city adopted effective May 1, 2025. Suburban cities run their own permit offices. Emergency and legally required systems often need drawings from a design professional with the permit, and the fire marshal may have a role in the final acceptance.

We pull the electrical permit, schedule the inspections and meet the inspector. In most of the San Antonio area the utility is CPS Energy, and any change to the service is coordinated with them.

Getting started

Start with the loads: what has to stay on because a code says so, and what you want to stay on because the business needs it. From there we can price the electrical work in writing before anything starts. See our commercial standby generators page for how we approach these jobs, our Generac generator installation page for the equipment we sell and install, and our generator installation service. For a smaller building, a Generac generator sizing visit is a good first step.