Generator power is not utility power
Three ways it differs, and only one of them is a surge.
1. Voltage sags and overshoots. When a large motor starts, a generator's output dips until the governor catches up; when the load drops away, it overshoots briefly. Utility supply has enormous inertia behind it and does neither to any meaningful degree.
2. Waveform quality varies. A conventional generator produces AC directly from a spinning alternator, and the result can be far from a clean sine wave. An inverter synthesizes it electronically and publishes a distortion figure — the architecture comparison covers why.
3. The wiring is temporary. Cords, inlet boxes and adapters that spend most of the year in a garage, assembled in the dark by someone who is cold. This is where open grounds and reversed polarity actually come from.
Diagnostics matter more than joules
A household surge strip is designed for one job: clamping a voltage spike arriving on a properly wired circuit. Its joule rating describes how much energy it can absorb before it stops protecting.
On a generator feed, the more likely problem is a wiring fault, and a joule rating says nothing about that.
| Fault | What it means | Consequence |
|---|
| Open ground | No grounding conductor continuity | An appliance fault energizes the casing instead of tripping a breaker |
|---|
| Reverse polarity | Hot and neutral swapped | Equipment energized where it should be neutral, even switched off |
|---|
| Open neutral | No neutral return path | Voltage imbalance across legs — can destroy 120V equipment |
|---|
| Low or high voltage | Supply out of range | Motors overheat; electronics behave unpredictably |
|---|
None of these is a surge, and none is detected by a surge strip. The first is the reason cords and adapters matter more than ground rods — a broken ground path is invisible until it matters.
The surge that actually causes damage
Here is the part most people have backwards.
The risky moment is not while the generator runs. It is when utility power returns — into a house where everything got switched on during the outage, where the supply may stabilize over several seconds, and where restoration switching upstream can produce genuine transients.
Which produces the most valuable advice on this page, and it costs nothing:
- Unplug sensitive electronics at the start of an outage, not the end. TVs, computers, anything with a control board.
- Leave one lamp on so you know when power returns.
- Bring things back gradually once the supply has been steady for a few minutes.
- Reverse the transfer switch sequence deliberately — circuits back to LINE one at a time rather than all at once.
What outages actually do to appliances covers the mechanisms in detail.
What to protect, and with what
| Equipment | What it needs |
|---|
| Whole generator feed | A diagnostic surge protector between the machine and the load |
|---|
| Desktop, NAS, recorder | A UPS with automatic voltage regulation |
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| TV and audio | A quality surge strip, or unplug them |
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| Fridge, freezer, furnace | Nothing special — motors tolerate this better than electronics, though modern control boards are less forgiving than they were |
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| Tool battery chargers | Clean waveform above all — this is an inverter-generator argument |
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| Anything on a power station | Already protected — the inverter output is regulated and clean |
|---|
That last row is worth noticing. A power station's output does not sag when a motor starts and does not overshoot when it stops — it is electronically regulated by design. Running sensitive equipment from a battery rather than directly from a generator sidesteps most of this page.
What surge protection does not do
- It does not fix a dirty waveform. A surge protector clamps spikes; it does not reshape a distorted sine wave. That is a generator specification, not an accessory.
- It does not protect against a direct lightning strike. Nothing at this price does. Unplugging does.
- It does not last forever. Surge protectors degrade with each event absorbed, and many keep passing power after they have stopped protecting. Units with a protection-status indicator are worth preferring, and any strip that has taken a big hit should be replaced.
- It does not replace grounding. Most surge protection works by diverting energy to ground, so on a circuit with an open ground it may not function at all — which is exactly why the diagnostics matter.
Where to spend, in order
- An inverter generator, if you are still buying. Clean power at the source beats filtering it afterwards, and the published THD figure is the specification to compare.
- A UPS on anything that must not blink. It handles voltage regulation and the transfer gap together.
- A diagnostic surge protector on the generator feed, if you are running a house or a job site through temporary wiring.
- Unplugging. Free, and more effective than anything above for the return-of-power transient.
The full accessory list puts this in order against everything else — and it sits below a carbon monoxide alarm, a cord and a cover, which are all more consequential.
