How to Run a Simulated Outage Test on a Service Visit

Why this matters

The weekly exercise never touches the transfer switch on most residential units. It proves the engine starts; it does not prove the switch senses a loss of utility, signals a start, moves its contacts, carries the house, and moves back. Those are the parts that fail quietly: a utility-sense fuse blown since the last storm, a stuck contactor, a load manager that never releases the air conditioner. A simulated outage on every service visit exercises the whole chain the way a real outage will, and a timing log turns "it worked" into numbers the next tech can compare against.

This card is the repeat test on a unit that is already commissioned. The first-time setup, settings and acceptance belong to a sibling. See related: Automatic Transfer Switch Commissioning Technique.

Before you open anything

Tell the household, in person, before the lights go out. A 15-second blink resets clocks and can knock out a desktop computer, a router, a garage door opener or a well pump mid-cycle. Ask directly about medical equipment: an oxygen concentrator, a CPAP or a home dialysis machine. Where one is in use, the test waits until the household has the device on its battery or backup supply, or it is rescheduled; a planned blink is not worth a medical event.

You will operate a disconnect, not open a panel. The test opens the utility supply to the transfer switch at a service disconnect: the main breaker of a service-rated transfer switch, or the separate service disconnect ahead of it. Operate it with its cover and dead front closed, standing to the side of the handle, in whatever PPE the shop's electrical safety program sets for operating that equipment under NFPA 70E (current edition). If the disconnect shows burn marks, a melted handle, buzzing or heat, do not operate it; that is a finding, and the test stops.

Do not pull the meter. The meter belongs to the utility, and pulling it to simulate an outage is not the tech's operation in most service territories.

Step 1: Read the settings before you start

On the controller, write down the timers this unit is set to: the utility-loss delay before an engine start (often a few seconds), the warm-up before transfer, the retransfer delay after utility returns, and the cooldown before shutdown. If a load manager is fitted, note its delays for each managed load, typically the air conditioner and sometimes a water heater or dryer. See related: Load Shed Module Programming.

Why first: the timing log is only useful against expected values. A transfer at 22 seconds means nothing until you know whether the unit was set for 7 seconds of warm-up or 20.

Confirm too that the controller is in automatic with no active alarms, the battery is charging and the utility indicator shows utility present. A unit not in auto will not start when you open the disconnect, and you will have caused an outage, not tested a response to one.

Step 2: Set up the readings

Put a meter or the controller's display where you can watch volts and hertz without standing in front of the generator's exhaust. Clip an amp clamp on a load leg at the transfer switch's load side only if that compartment is already accessible without opening energized covers; otherwise use the controller's current display if it has one. Start a stopwatch or note clock time at each event.

Have the thermostat set to call for cooling or heat so the heavy load, usually the air conditioner or heat pump, is asking to run during the test. A test with no heavy load proves the transfer but not the generator's ability to start the load it was sized for.

Step 3: Open the utility feed and time each stage

Open the disconnect and start the clock. Record each event as it happens:

1. Utility opened. The house goes dark.
2. Engine crank. The time from step 1 should match the utility-loss delay.
3. Engine running. Note cranks needed. One start attempt that catches in a few seconds is normal; repeated cranking is a battery, fuel or ignition finding.
4. Transfer. The switch moves and the house comes back. From step 3, this should match the warm-up.
5. Load carried. Volts and hertz on generator, and amps if you can read them.
6. Managed loads released. Each load the manager holds off should come on after its set delay. Watch the voltage and frequency dip as the compressor starts, and how fast they recover.

Hold the house on generator long enough to see every managed load come on and run, which on most units means several minutes past the longest delay.

Step 4: Restore utility and time the return

Close the disconnect, noting the time, and record:

1. Utility restored.
2. Retransfer. The switch moves back after the retransfer delay. On an open-transition switch, which is nearly every residential unit, the house blinks once more.
3. Cooldown. The engine runs unloaded for its set cooldown.
4. Shutdown and standby. The engine stops and the display returns to ready in automatic.

The timing log

 SIMULATED OUTAGE   22 kW air-cooled, NG, 200 A SE-rated ATS
 settings read: utility-loss 5 s, warm-up 7 s,
 retransfer 15 s, cooldown 60 s, AC hold-off 300 s

 EVENT                  CLOCK      ELAPSED  EXPECTED
 1  utility opened      10:02:00   0 s      -
 2  engine crank        10:02:05   5 s      5 s
 3  engine running      10:02:08   8 s      1 crank
 4  transfer to gen     10:02:15   15 s     8 + 7 = 15 s
 5  load carried        241 V  60.1 Hz  L1 38 A  L2 31 A
 6  AC released         10:07:15   315 s    15 + 300 s
    dip 228 V  58.9 Hz, back to 240 V  60.0 Hz in 2 s
 7  utility restored    10:12:00
 8  retransfer          10:12:15   15 s     15 s
 9  cooldown ends       10:13:15   60 s     60 s
 10 stop, READY AUTO    10:13:20
 house dark: 15 s going out, one blink coming back

The log closes against the settings at every line. The house was dark 15 seconds, made of the 5-second utility-loss delay, 3 seconds of cranking and the 7-second warm-up. The air conditioner was held off 300 seconds after transfer and released at 315 seconds from the start. Retransfer came 15 seconds after the utility returned, and the engine ran 60 seconds unloaded before stopping.

What the dip says. The compressor start pulled the generator down to 228 volts and 58.9 hertz and it recovered in 2 seconds. Whether that dip is acceptable depends on the generator's rating and the compressor's starting load, which the sizing and inrush cards own. What this test adds is a baseline: next year's test on the same unit should show about the same dip. A dip that has grown, or a compressor that stalls and trips the generator on underfrequency, says something changed: the compressor is wearing, a hard-start kit has failed, or the engine is down on power. See related: How to Measure AC Compressor Inrush with a Clamp Meter.

Step 5: Confirm the unit is back in automatic

Read the controller one more time: automatic mode, no active alarms, utility present, battery charging. Then look at the house: clocks, the router, the garage door, any well or sump pump the customer relies on. A sump pump that lost its reset can flood a basement in the next storm while the generator works perfectly.

Leave the household a short note of what happened and when, especially if the test reset anything they will notice later.

File the timing log on the job record against the unit's serial number, beside last year's. The value of the log is the comparison: a crank that took one attempt last year and three this year, or a warm-up that crept from 7 seconds to 11, is a finding on a unit that still "worked".

What changes the result

The engine does not start at all. Close the disconnect immediately so the house is not left dark, then diagnose with utility present. The usual culprits are the controller not actually in auto, an active alarm blocking the start, or a battery that cannot crank; a battery that read fine at rest can still sag under the starter. See related: Diagnose Generator No-Start.

It starts but never transfers. The engine reaches speed and the house stays dark past the warm-up. The transfer signal or the switch's own mechanism has failed; close the disconnect to restore the house and diagnose the switch with the procedure the commissioning card uses.

It transfers but does not retransfer. The house stays on generator after the utility is restored. Do not leave the site that way; a unit carrying the house in a non-outage burns fuel and masks a utility-sense fault. Check the sensing and the retransfer timer, and if it cannot be put right, place the unit in a state the maker's manual allows (often manual transfer back to utility) and write it up.

Timers that drifted. A setting that no longer matches the commissioning record (warm-up stretched, retransfer shortened) is worth asking about. Somebody changed it, and the customer or the last tech may have had a reason.

How to verify you got this right

• Every event in the log has a clock time, and every timed interval matches the setting read in step 1, or the difference is written down.
• The heavy load was calling during the test and started on generator, with the dip and recovery recorded.
• The unit is in automatic, no alarms, utility present, battery charging, before you leave.
• The household's sensitive loads (pumps, medical devices, network) are back as they were.

References

• NFPA 70E, Standard for Electrical Safety in the Workplace, current edition, for operating service disconnects and PPE
• The generator and transfer switch makers' manuals for timer settings, open-transition behavior and allowed manual operation
• See related: Automatic Transfer Switch Commissioning Technique; Load Shed Module Programming; How to Measure AC Compressor Inrush with a Clamp Meter; Diagnose Generator No-Start