Automatic Transfer Switch Installation

An automatic transfer switch monitors the normal electrical source.

When normal power is lost, the system can:

1. Detect the utility failure

2. Signal the standby generator to start

3. Confirm that generator power is available

4. Transfer the connected loads to the generator

5. Continue monitoring normal utility power

6. Transfer the loads back when normal power returns

7. Allow the generator to complete its cooldown cycle

The exact sequence depends on the equipment and system design.

The important point is that the ATS controls how the building moves between its normal and backup power sources.

A Generator Is Only Part of the Backup-Power System

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Customers sometimes focus almost entirely on the generator.

But a complete standby-power system can include:

• Generator

• Automatic transfer switch

• Service or distribution equipment

• Emergency panels

• Critical-load panels

• Feeders

• Control wiring

• Fuel system

• Monitoring

• Protective devices

If any one of these pieces does not operate correctly, the expected backup loads may not receive power.

OTC evaluates the complete electrical path instead of treating the ATS as an isolated piece of equipment.

An ATS can be used to support different backup-power strategies.

Whole-Building Backup

The generator and transfer equipment are designed to support a large portion or potentially all of the facility's electrical load.

Critical-Load Backup

Selected systems are separated onto dedicated emergency or standby distribution.

Those loads may include:

• Refrigeration

• Servers

• Communications

• Security

• Selected HVAC

• Building controls

• Pumps

• Critical production equipment

• Emergency systems

Backing up only the loads that actually need to operate can sometimes reduce generator size and overall system cost.

The right strategy depends on the building and what the customer considers critical.

Automatic transfer switches should be selected around the electrical system they serve.

Considerations may include:

• System voltage

• Phase

• Amperage

• Connected load

• Generator size

• Service configuration

• Available fault current

• Equipment ratings

• Switching arrangement

For engineered backup-power systems, ATS selection is coordinated with the project electrical engineer and approved system design.

Some systems place the ATS at or near the building's service entrance.

Depending on the electrical design, the transfer equipment may be required to perform additional service-equipment functions.

These projects can affect:

• Utility service

• Main disconnecting means

• Metering

• Grounding and bonding

• Downstream distribution

• Generator feeders

OTC coordinates the installation around the approved design and serving utility requirements where applicable.

Another common arrangement uses a transfer switch to serve a dedicated critical-load panel.

The electrical path may look like:

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

This allows the backup system to focus on specific systems without carrying the entire building.

The critical loads should be identified before the system is designed.

The ATS does more than move electrical power.

In many standby-generator systems, it also provides the signal that tells the generator when normal utility power has failed and when the generator should start.

If that control path has a problem, the generator may not respond correctly even when the utility source is lost.

OTC checks both the power and control portions of the system when troubleshooting transfer problems.

Transfer switches may eventually require replacement because of:

• Mechanical failure

• Contact deterioration

• Control-board failure

• Heat damage

• Water intrusion

• Obsolete equipment

• Difficulty sourcing replacement parts

• Inadequate capacity

• Generator-system upgrades

The replacement should be coordinated with the existing generator and downstream electrical system rather than selected solely by matching the old enclosure size.

An automatic transfer switch should be evaluated if:

• Generator starts but loads do not transfer

• Building does not return correctly to utility power

• Transfer takes unusually long

• Switch produces abnormal noise

• Equipment shows heat or discoloration

• Transfer fails intermittently

• Controls show recurring alarms

• Manual operation is inconsistent

• Parts are becoming difficult to obtain

Intermittent transfer problems deserve attention because the system may appear normal until the next real outage.

A backup-power system should be tested under conditions that verify the complete transfer sequence.

Depending on the system and operating requirements, testing may confirm:

• Utility-loss detection

• Generator-start signal

• Generator availability

• Transfer to backup source

• Voltage at the supported loads

• Return to normal utility source

• Generator cooldown sequence

• ATS indication and controls

Simply starting the generator does not prove the transfer system works.

The loads need to actually move to the backup source as intended.

One of the most important concepts in standby power is that generator operation and building backup power are not the same thing.

The generator can start and produce proper voltage while a problem with:

• ATS controls

• Transfer contacts

• Breakers

• Feeders

• Distribution

• Control wiring

prevents that power from reaching the building.

OTC troubleshoots the system from the generator through the transfer equipment and downstream distribution to determine where the backup-power path is failing.

Installing or replacing a transfer switch often requires interruption of normal building power.

OTC coordinates shutdowns around:

• Business operations

• Tenants

• Refrigeration

• Servers

• Security

• HVAC

• Production equipment

• Critical building systems

For larger facilities, the shutdown and cutover plan should be developed well before installation begins.

Some properties cannot tolerate a prolonged complete outage while an existing transfer switch is being replaced.

Depending on the facility, temporary-power planning may be considered for selected loads.

That may include:

• Refrigeration

• Communications

• Security

• Critical equipment

• Limited business operations

Temporary power is project-specific and should be planned around the actual loads that need to remain operational.

For new standby-generator projects, the ATS should be coordinated early with:

• Generator size

• Critical-load strategy

• Existing service

• Distribution equipment

• Equipment location

• Feeder routing

• Control wiring

• Future expansion

The generator and ATS should be selected as parts of the same backup-power system rather than separate equipment purchases.

A new ATS can also be part of an upgrade to an existing generator system.

Before replacing or modifying the transfer equipment, OTC verifies:

• Generator voltage

• Generator capacity

• Existing feeder sizes

• Control compatibility

• Downstream loads

• Service configuration

Older generators and newer transfer equipment may require additional coordination to ensure the control and power systems are compatible.

Larger facilities may use more than one automatic transfer switch.

Separate switches may serve different categories of loads, buildings, or distribution systems.

This can allow the backup system to prioritize different portions of the property and create more flexible distribution.

The transfer strategy should be developed as part of the engineered electrical design.

An ATS and UPS perform different jobs.

Automatic Transfer Switch

Moves loads between normal utility power and generator power.

UPS

Provides immediate battery-backed power without waiting for the generator to start and transfer.

For sensitive equipment, both systems may be used together.

The UPS keeps the equipment operating during the short gap while the generator starts and the ATS completes the transfer.

Transfer equipment should not be ignored until a utility outage occurs.

Preventive maintenance can help identify:

• Loose connections

• Heat

• Contact deterioration

• Control issues

• Battery or control-power problems

• Mechanical problems

• Environmental damage

Backup equipment is difficult to evaluate by appearance alone.

Functional testing is what demonstrates whether the system will actually operate when normal power is lost.

A complete ATS project may involve:

• Existing-system evaluation

• Critical-load identification

• Load review

• Engineering where required

• Generator coordination

• ATS selection

• Feeder installation

• Control wiring

• Shutdown planning

• Equipment installation

• Transfer-sequence testing

• Voltage verification

• Final labeling and documentation

OTC coordinates the electrical construction so the normal source, standby source, transfer equipment, and downstream loads operate together.