Standby Generators and Transfer Switches for Every Trade

Why this matters

A permanently installed standby generator is the one machine on a house that starts itself with nobody touching it. It does it when the utility drops, and it does it on a schedule to keep itself healthy, often on a weekday morning when the only people around are a landscaping crew, a painter on a ladder beside it, or a tech who just turned off what he thought was "the power". The engine is hot, it makes carbon monoxide, and when it runs it puts the house's wiring back under power. This card is what every trade working near one needs to recognize.

For how a generator's power can travel back up the utility lines, see related: Generators, Backfeed and the Lineworker. For the different kinds of transfer equipment and how to tell them apart, see related: Generator Transfer Switch Types Reference. This card is about the installed unit and the yard and wiring around it.

What the installation is

A standby generator sits outside on a pad, in a metal enclosure that looks like an oversized air conditioner condensing unit. It runs on natural gas from the house's meter or on propane from a tank, through a fuel line that is usually buried or run along the wall. A conduit carries its output and control wiring to an automatic transfer switch (ATS), a box usually mounted beside the meter or near the main panel.

The ATS is the brain. It watches the utility voltage. When it sees the utility fail, it signals the generator to start, waits for the engine to come up to speed, and then moves the house's load from the utility to the generator. When the utility returns and stays steady, it moves the load back and lets the engine cool down and stop.

Recognize the controller. The generator has a small control panel under its lid, usually with three states: Auto, Off and Manual (sometimes Run). Auto is normal. Nobody but the homeowner or the owning trade, the generator dealer or electrician, changes it.

Why it starts by itself

An outage. In Auto, the ATS starts the engine within seconds of losing utility power, after a short delay set to ride through a flicker. Nobody presses anything.

Something that looks like an outage. The ATS cannot tell a storm from a tech. Turn off a utility-side disconnect, pull the meter, or open a main that sits ahead of the ATS, and the ATS sees exactly what it sees in a storm. The engine starts, the switch transfers, and the house is live again from the generator, usually in well under a minute. A tech who "killed the power at the main" to work on a circuit can be holding that circuit when it comes back. Which disconnect does what depends on how that house was wired, which is why the answer to "is this circuit dead" with a standby generator on site comes from the owning trade, not from the position of one handle.

The exercise cycle. Engines that sit for months fail when they are finally needed, so the controller starts the unit on a schedule, commonly once a week or once every other week, for a short run (often somewhere around 5 to 20 minutes, set on the controller). On many units the exercise runs the engine without transferring the house's load. The homeowner usually knows the day and time; the controller shows it too. To a crew working beside the unit, the exercise sounds like it starting for no reason.

Why loads through the transfer switch stay live

When the generator is running and the ATS has transferred, every circuit fed through the ATS is energized from the generator. On a whole-house installation that is the whole house. On a partial installation, it is whatever is in the panel the ATS feeds.

That has two consequences for other trades:

• "The power's out" is not "the circuit is dead". During an outage at a house with a standby generator, the receptacles, the furnace, the well pump and the lights may all be live. Treat them as live.
• The fix you did during the outage gets tested at the transfer back. When the utility returns, the ATS swaps sources. Anything loose you left in the circuit sees the switch-over. That is an electrician's concern, but a reason not to leave temporary connections on a backed-up circuit.

If your work needs a circuit dead in a house with a standby generator, it is an electrician's isolation, and that electrician will deal with the generator as part of it.

The exhaust side, and why landscapers keep clear

The engine's exhaust leaves the enclosure through an outlet on one side or end, and it is hot and full of carbon monoxide (CO), an odorless gas that kills at concentrations you cannot smell or see.

CO at openings. The manufacturer's manual sets how far the unit sits from doors, windows, vents and intakes; a common figure in those manuals is 5 ft from any operable opening, but the manual for the actual unit governs, along with NFPA 37 in the edition your jurisdiction has adopted for stationary engines. Anything you add that creates a new opening near the unit (a dryer vent, a crawlspace vent, a new window) or that holds exhaust against the house (a fence panel, a dense hedge, a lattice screen) changes where the CO goes. A CO alarm sounding inside the house while the generator runs means everyone goes outside into fresh air and calls 911.

Heat and fire. The exhaust outlet and the enclosure near it get hot enough to ignite dry leaves, grass clippings, pine straw and wood mulch piled against them. A crew that spreads wood mulch up to the pad or blows leaves into the corner beside it has built the fuel for a fire that the next exercise lights.

Airflow in. The enclosure pulls cooling and combustion air through louvers. Shrubs, clippings, a tarp, or soil pushed up against them make the engine overheat and shut down, which the homeowner finds out during the next outage.

What is buried near it. The fuel line from the gas meter or the propane tank and the conduit to the ATS are the homeowner's private lines. A public utility locate does not mark them. See related: How to Find the Private Lines a Utility Locate Will Not Mark.

Water. Do not aim irrigation heads or a pressure washer into the enclosure.

Worked example: the planting bed beside the generator

A landscaping crew is installing a planting bed along the east side of a house, 30 ft long by 4 ft deep, edged, with wood mulch and a row of evergreens. The homeowner's other request: "Hide the generator." The unit sits on its pad along that same wall, 18 in off the siding, with its exhaust outlet on the end facing the backyard and its louvered service side facing out into the yard. The gas meter is at the front corner of the house, about 25 ft from the unit.

What starts it, and when. The crew lead asks the homeowner, who says it "runs on Tuesdays around noon". The controller under the lid confirms an exercise every Tuesday at 12:00 for 12 minutes. The crew is on site Tuesday from 8:00. Nobody on the crew changes the controller to Off to keep it quiet. They plan the work beside the unit for the morning, and at 11:50 they move to the other end of the bed and stay there until 12:12 or until it stops. At 12:00 it starts on schedule, and it stops 12 minutes later.

What the manual says. The manual is in a sleeve inside the lid. Say it calls for 5 ft clear of plants and structures at the exhaust end and 3 ft clear on the service side for maintenance access (illustrative; read the real manual). The crew's bed plan put the evergreen row 2 ft in front of the service side and planted the bed's last shrub 2 ft past the exhaust end. Both fall short of the manual's clearances, by 1 ft on the service side and 3 ft at the exhaust end. The evergreens move out to 3 ft from the service side, and the bed stops 5 ft short of the exhaust end.

Mature size, not planted size. An evergreen planted 3 ft out from the service side with a 4 ft mature spread grows to within 1 ft of the louvers, measured from its trunk: 3 ft minus half of 4 ft is 1 ft. To keep the full 3 ft clear at maturity, the crew moves the row out to 5 ft (5 minus 2 is 3 ft off the louvers), or sets it at 4 ft with a variety whose mature spread is 2 ft or less (4 minus 1 is 3 ft). Hiding the unit is done with distance, not by planting tight.

What goes on the ground. Wood mulch stops where the bed stops. The 5 ft at the exhaust end gets river rock or stays lawn, so there is nothing to ignite. The crew blows the clippings away from the unit at the end of the day, not toward it.

What they dig near. The edging trench runs past the pad and toward the front corner, the same route the gas line would most likely take from the meter. The crew hand digs within a few feet of the pad and along the wall toward the meter, rather than running a trencher there, because neither the fuel line nor the ATS conduit is on the utility's locate.

What would change the answer.

• Propane rather than natural gas. The fuel line runs from the tank, which may be across the yard, and the dig risk moves to wherever that line runs. Ask the homeowner or the propane supplier where the tank's line goes before trenching anywhere between the tank and the unit. See related: Propane Homes: What Every Trade Should Know.
• A portable generator and an interlock instead of a standby unit. Nothing starts by itself, but the generator wheeled out and plugged into an inlet during an outage carries the same CO and backfeed hazards, and you can find it running in a garage doorway. See related: Generators, Backfeed and the Lineworker.
• The exhaust end facing the bed instead of away from it. The 5 ft no-mulch zone now lands inside the planned bed. That is a redesign of the bed around the unit, not a trim of one shrub.

The failure mode. Not the exercise surprising someone. It is a beautiful bed that grows into the louvers over two summers, a unit that overheats and shuts down in the first long outage, and a homeowner who finds out at the worst possible time. Or a mulch fire on an August Tuesday.

What you never do

• Switch the controller to Off, or open the enclosure, to work near it. The owning trade does that.
• Lean ladders, stack materials, or park equipment against it.
• Run a gas-powered tool, a portable generator or a vehicle idling in the same corner on a still day, adding to the CO in a pocket.
• Assume a circuit is dead because the house's utility power is off.

If something looks wrong (an exhaust outlet blocked by a nest, a fuel smell near the unit, the unit running when there is no outage and no exercise due), tell the homeowner and call the generator dealer. For a fuel smell near the unit or the meter, everyone moves away from it, nobody operates switches or starts engines near it, and the call goes to the gas utility or the propane supplier from a safe distance.

References

• The generator's installation and owner's manuals for clearances, exercise settings and controller states
• NFPA 37, Standard for the Installation and Use of Stationary Combustion Engines, as adopted by your jurisdiction, which binds the installation and reaches other trades through the clearances it sets
• See related: Generators, Backfeed and the Lineworker
• See related: Generator Transfer Switch Types Reference
• See related: How to Find the Private Lines a Utility Locate Will Not Mark