Homes with Solar, Batteries or Generators Already Installed

Why this matters

For a century a house had one source of power, and turning off the main breaker made it dead. A house with solar, a battery or a generator has two, three or four sources, and the main breaker turns off only one of them. The rooftop array is producing whenever light hits it, the battery keeps chosen circuits alive when the grid is gone, and a standby generator starts by itself the moment it senses the utility drop, including when you are the one who dropped it. Every trade that touches a circuit, a condenser, a water heater or a well pump in these homes needs to identify every source before assuming anything is off. This card covers how to recognize what is installed and who is responsible for each piece; the isolation procedure itself belongs to its own SOP.

Safety first: what you do before anything else

• Assume nothing is dead because the main breaker is off. Prove the specific conductors you will touch are dead with a meter checked on a known live source before and after, per NFPA 70E-2021, 120.5, with the lockout and work practices at 29 CFR 1910.333(b)(2). If nobody on site is a qualified person for that work, it goes to an electrician.
• Put a standby generator's controller in the off position before opening any utility-side disconnect, so it cannot start and transfer onto the circuits you are working on.
• A battery that is hot, swelling, hissing, smoking or giving off a sharp chemical smell is a thermal runaway risk. Everyone leaves the house, nobody opens the enclosure or sprays water on it, and someone calls 911 from outside and tells the dispatcher it is a lithium-ion battery system.
• Never open a battery or inverter enclosure. They hold stored energy and are serviced only by the installer or the manufacturer's authorized service.
• Never disconnect a solar DC connector under load. It can draw an arc. DC circuits are isolated at the inverter or the labeled disconnect, in the sequence the manufacturer specifies.

How the sources connect

One common layout for a home with all three, simplified. Others exist, and the labels on site, not this drawing, govern:

UTILITY -> METER -> GATEWAY -----> MAIN PANEL <- INLET
                  (grid switch)     |              ^
                       |        non-backup     GENERATOR
                       |          loads      (interlocked)
                       v
              BACKUP SUBPANEL <- BATTERY + INVERTER
                |          ^
   condenser, fridge,      +-- PV INVERTER <- ROOF ARRAY
   furnace blower              (DC live whenever lit)

Read it for where power can arrive at a given circuit. In this layout, the condenser is fed from the backup subpanel. Opening the main breaker in the main panel does nothing to it. Losing the grid does nothing to it either: the gateway opens its grid switch, and the battery and the solar array keep the backup subpanel energized as a small, separate grid, called an island. The generator feeds only the main panel, through an interlock that physically prevents its inlet breaker and the main breaker from both being on.

Recognizing what is installed

Walk the outside and the panel before you open anything. Code-required labels do much of the work, if you read them.

• At the meter and service equipment: a label stating the home has a solar system or multiple sources, a directory or plaque showing where each disconnect is, and, for solar, a rapid shutdown label naming where the initiating switch is.
• Solar inverter: a string inverter on a wall near the meter or in the garage, or microinverters under each panel on the roof, in which case the conductors coming off the roof are already AC.
• AC disconnect for the solar: a labeled switch near the meter or inverter.
• Battery and gateway: a wall-mounted cabinet, and a second enclosure near the meter that switches the house between grid and battery.
• Backup subpanel: a separate panel, often labeled "backed-up loads" or similar. Find out which circuits are in it.
• Generator: a standby unit outside on a pad with an automatic transfer switch near the panel, or a power inlet box on the exterior wall for a portable generator, with an interlock plate on the main panel or a manual transfer switch.
• In the main panel: a back-fed breaker labeled for the solar or the battery, often at the opposite end of the bus from the main breaker.

Rapid shutdown. Since the 2014 edition, NEC 690.12 has required rooftop solar on buildings to have a rapid shutdown function, operated from a labeled initiator, that reduces the voltage on the system's conductors. In the 2017 and later editions, conductors outside the array boundary must drop to 30 volts or less within 30 seconds of initiation, with a separate, edition-dependent rule inside the array. Rapid shutdown is for firefighters and is not a lockout: the modules themselves still produce voltage in light, and the DC wiring within the array can remain energized. Your jurisdiction's adopted edition decides what an older system was built to.

A found hazard: the backfeed cord. A double-ended cord, plugged from a portable generator into a dryer or range receptacle, energizes the house wiring without any transfer equipment. It can energize the utility's lines and kill a lineworker, it can energize circuits a tech believes are dead, and its exposed male plug is live whenever the generator runs. If you find one, do not use it, tell the homeowner plainly what it does, and note it on the job record. Transfer equipment is required for optional standby systems under NEC Article 702.

Who is responsible for each piece

Before you touch a source or anything that could affect it, know whose it is. Damage or a voided warranty becomes your problem otherwise.

For your own work, the practical rule is simple: you may open a breaker or a disconnect to isolate your own circuit, but you do not reconfigure, relocate, rewire or service another party's source equipment.

Worked example: a condenser replacement in a four-source home

An HVAC crew arrives to replace a failed condenser. The home has an owned rooftop solar system with a string inverter, a battery with a gateway and a backup subpanel, and a portable generator inlet with an interlock on the main panel. Four possible sources: the utility, the solar, the battery and the generator.

Identify. The tech walks the exterior: the placard at the meter shows the solar AC disconnect, the gateway and the rapid shutdown switch. The generator inlet box is on the garage wall; the generator itself is in the garage, off and unplugged. Inside, the main panel has a back-fed breaker labeled for the gateway, and the backup subpanel's directory lists "condenser" and "air handler."

Find the circuit's sources. Because the condenser is in the backup subpanel, it can be fed by the utility through the gateway, by the battery, and by the solar through its own string inverter. It cannot be fed by the generator, which is wired only to the main panel. So three of the four sources can reach this circuit, and opening the main breaker would have removed none of them.

Isolate the circuit itself. The tech opens the condenser breaker in the backup subpanel and the condenser's outdoor disconnect, locks and tags both, and proves dead at the disconnect's load side with a meter checked on a known live source before and after, per NFPA 70E-2021, 120.5, and 29 CFR 1910.333(b)(2). The capacitor in the old unit is discharged with a resistor-type tool and verified at zero volts before handling. No other source is touched: the battery and solar stay in service, the fridge stays cold, and nobody needed to work on the solar or battery equipment.

What would have changed it. If the condenser had been on the main panel's non-backup side, its sources would have been the utility and, during an outage, the generator through the interlock. Then confirming the generator is off and its cord unplugged becomes part of the job. If the house had a standby generator with an automatic transfer switch instead, its controller goes to off before anyone opens anything upstream.

Return to service. The tech stands to the side of the disconnect, not in front of it, removes his own locks, closes the breaker and the disconnect, and watches the new condenser start. He checks the gateway's display or app shows the system in its normal grid-connected state, and notes on the job record which breakers were opened and that all were restored.

The failure this avoided: the classic one, where the main breaker is opened, the condenser circuit is assumed dead, and the backup subpanel is still live on battery.

How to check you identified every source

Before opening any circuit in one of these homes, a tech should be able to name, for that circuit, every source that can reach it and the device that isolates each one. If any source on the placard cannot be traced to a known effect on the circuit, stop and trace it, or call the installer. For the procedure itself, see related: The Multi-Source Power Home Isolation SOP.

References

• See related: The Multi-Source Power Home Isolation SOP
• See related: Off-Grid and Battery-Backed Homes
• NEC 690.12 (rapid shutdown), Article 702 (optional standby systems) and Article 706 (energy storage systems), in the edition your jurisdiction has adopted
• NFPA 70E-2021, 120.5, and 29 CFR 1910.333(b)(2), for proving conductors dead and electrical lockout
• Battery and inverter manufacturers' installation and emergency response documentation