Commercial Standby Generator Installation

Before sizing the generator, the facility needs to determine which loads should continue operating during an outage.

Those loads may include:

• Refrigeration

• Servers

• Network equipment

• Security systems

• Building controls

• Selected HVAC

• Pumps

• Commercial kitchen equipment

• Production equipment

• Communications

• Emergency systems

• Lighting

Not every load has the same importance.

A generator designed around actual operational priorities can be very different from one sized to support every electrical load in the building.

Commercial generator systems generally fall into two broad strategies.

Whole-Building Backup

The generator and transfer equipment are sized to support a large portion or potentially all of the facility.

This may make sense for buildings where extended power loss creates major operational or financial consequences.

Selected-Load Backup

Only specific critical systems are connected to the standby-power system.

This may reduce:

• Generator size

• Fuel consumption

• Transfer-equipment requirements

• Electrical-distribution cost

OTC helps identify the electrical infrastructure required for whichever strategy the project uses.

Generator sizing should consider more than the sum of the breaker ratings.

Depending on the project, factors may include:

• Actual connected loads

• Expected simultaneous operation

• Motor starting

• HVAC

• Refrigeration

• Equipment starting characteristics

• Generator voltage

• Phase

• Future loads

• Desired backup duration

For larger or engineered systems, the final generator sizing and system design are coordinated with the project engineer and generator manufacturer requirements.

A complete commercial standby-power system may include:

• Generator

• Automatic transfer switch

• Service or distribution modifications

• Emergency or standby panels

• Feeders

• Breakers

• Disconnects

• Control wiring

• Generator starting system

• Fuel system

• Monitoring

• Grounding and bonding

If one of these systems fails, the generator may start while the building still does not receive backup power.

That is why OTC looks at the complete backup-power path.

The automatic transfer switch, or ATS, is one of the most important parts of the standby-power system.

When normal utility power is lost, the ATS can:

1. Detect the power failure

2. Signal the generator to start

3. Verify generator power

4. Transfer the supported loads

5. Monitor the return of utility power

6. Transfer the building back to the normal source

7. Allow the generator to complete its cooldown cycle

A generator that starts but cannot transfer power to the intended loads does not provide a complete backup solution.

Selected-load systems may use dedicated standby or critical-load distribution.

A common arrangement may look like:

Utility + Generator → ATS → Critical-Load Panel → Selected Equipment

That panel may serve loads such as:

• Refrigeration

• Communications

• Security

• Servers

• Selected HVAC

• Controls

• Critical equipment

Separating these loads can provide a cleaner and more manageable backup-power strategy.

The generator needs to match the electrical system it is intended to support.

Commercial generator systems may involve:

• 208Y/120V

• 480Y/277V

• Single-phase

• Three-phase

OTC verifies the facility distribution and supported loads before coordinating the generator connection.

If different voltages are required downstream, the backup system may also need transformers or additional distribution equipment.

Adding a standby generator to an existing building can require substantial modifications to the electrical distribution.

Depending on the system, the project may involve:

• New ATS

• New main distribution

• Dedicated standby panel

• Feeder modifications

• Service-equipment changes

• New breakers

• Transformer coordination

The generator cannot simply be connected anywhere convenient.

The connection point needs to work with the building's existing service and distribution system.

Some generator projects integrate the transfer equipment near the building service entrance.

These installations may affect:

• Main service equipment

• Metering

• Utility coordination

• Main disconnects

• Grounding and bonding

• Building distribution

Larger projects are coordinated with the electrical engineer, utility, and AHJ as required.

Generator location affects both the electrical and overall project scope.

The location may need to account for:

• Distance from electrical equipment

• Generator feeder routing

• Equipment access

• Maintenance access

• Exhaust

• Noise

• Property layout

• Required clearances

• Fuel-system routing

• Physical protection

The generator should be placed where it can operate and be maintained without creating unnecessary difficulty for the building.

Commercial standby generators may operate from fuel sources such as:

• Natural gas

• Diesel

• Propane

The electrical generator system and the fuel system need to be coordinated together.

OTC handles the electrical scope and coordinates with the appropriate fuel-system or mechanical contractors where separate specialty work is required.

Fuel availability and system performance matter because a generator cannot provide reliable backup power if the fuel source cannot support the required operating conditions.

A generator that starts does not automatically mean it will remain available throughout an outage.

Standby generators include protective systems designed to shut the unit down if certain unsafe or abnormal conditions occur.

Problems can involve:

• Generator controls

• Safety switches

• Fuel supply

• Starting system

• Transfer controls

• Electrical protection

That is why functional testing of the entire backup-power system matters.

A proper generator test should verify more than whether the engine starts.

Depending on the system, testing may confirm:

• Loss of utility source

• Generator start

• Generator voltage

• ATS transfer

• Power at critical loads

• Equipment operation

• Return to utility

• Generator cooldown

• System alarms and controls

The important question is:

Did the equipment that was supposed to stay operational actually stay operational?

Existing standby generators may need replacement because of:

• Mechanical failure

• Electrical failure

• Obsolete equipment

• Poor parts availability

• Increased building load

• Repeated reliability problems

• Major building renovations

Replacement should include evaluation of the existing:

• ATS

• Feeders

• Breakers

• Distribution

• Control wiring

• Supported loads

A new generator should not automatically be connected to an old system without verifying that the rest of the backup infrastructure is still appropriate.

A facility may want to add new equipment to an existing standby system.

Before doing so, OTC evaluates:

• Generator capacity

• Existing critical loads

• ATS capacity

• Feeder capacity

• Distribution

• Starting characteristics of the new equipment

Available breaker space alone does not prove the generator can support the additional load.

Generators and UPS systems solve different problems.

UPS

Provides immediate battery-backed power for equipment that cannot tolerate even a brief interruption.

Standby Generator

Provides longer-duration backup after the generator starts and the ATS transfers the load.

Facilities with sensitive equipment may use both.

The UPS carries the load during the short period between utility failure and generator transfer.

Connecting a standby generator system may require temporary interruption of normal building power.

OTC coordinates shutdowns around:

• Tenants

• Business operations

• Refrigeration

• Servers

• Security

• HVAC

• Production equipment

• Critical controls

For larger projects, shutdown planning begins well before the final connection.

Temporary generators can sometimes be used when a building must maintain selected loads during a planned outage or major electrical project.

Temporary power can be expensive and still requires careful planning for:

• Connections

• Load requirements

• Fuel

• Distribution

• Equipment compatibility

It should not be assumed that a temporary generator can simply be delivered and support the building without preparation.

Backup-power equipment spends most of its life waiting for an outage.

That makes maintenance and periodic functional testing especially important.

A generator system may appear completely normal until utility power is actually lost.

Preventive maintenance can help identify issues involving:

• Generator starting

• Controls

• ATS operation

• Electrical connections

• Batteries

• Breakers

• Distribution

before the facility is depending on the system during a real outage.

When a new generator system is being installed, it can make sense to consider reasonable future needs.

Potential future loads may include:

• Additional refrigeration

• More HVAC

• Production expansion

• Additional critical equipment

• Building expansion

The goal is not to unnecessarily oversize the generator.

It is to avoid installing a backup system that immediately becomes the next limitation.

A complete commercial standby-generator project may include:

1. Critical-load evaluation

2. Existing electrical-system review

3. Preliminary load planning

4. Engineering where required

5. Generator and ATS selection

6. Fuel-system coordination

7. Distribution modifications

8. Generator feeder installation

9. Control wiring

10. Equipment installation

11. Shutdown and final connection

12. Transfer-sequence testing

13. Load verification

14. Final labeling and documentation

OTC coordinates the electrical construction so the generator, ATS, distribution, and critical loads operate as one complete backup-power system.