The Multi-Source Power Home Isolation SOP

Purpose

A house with solar, a home battery or a generator has more than one way to put voltage on a conductor, and opening the main breaker removes exactly one of them. This procedure guarantees that before anyone touches a conductor, every source has been found, opened by the method that stops that source, tagged, and proven dead at the point of work. Without it, the classic event is a tech who opens the main, hears the house go quiet, and puts a screwdriver on a backed-up circuit the battery kept live without a flicker. The dead test at the work point is the only step that catches the source nobody listed.

Scope

Covers: any work exposing branch-circuit or feeder conductors or a panel interior, in a dwelling with utility service plus any of: grid-tied solar, a battery energy storage system, a standby generator with an automatic transfer switch (ATS), or a portable generator inlet.

Does not cover: the PV array, DC string conductors, battery enclosure interior or inverter internals (the installer's or manufacturer's; this SOP isolates them, it does not open them); anything on the utility side of the meter; and mechanical lockout of a single appliance where no panel or feeder is opened, which your shop's general lockout program owns.

Roles and responsibilities

The handoff that matters most is customer to lead tech at step 2: a customer who has lived through outages knows things no permit shows.

Procedure

1. Pull the paper before arrival. The office looks up the address's permits and any install packet the customer can send, and writes on the ticket every source those documents show: utility, PV with inverter type, battery, standby generator with ATS location, portable inlet. Acceptance: the ticket carries a source list, even if it reads "utility only, no records found". Wrong looks like a blank field; the tech treats a blank as unknown, never as none. Skipping it means arriving without the installer's shutdown sequence, which some battery systems require in a specific order.

2. Survey the property for sources, outside first. Walk the exterior (meters, labeled AC disconnects, rapid shutdown initiator, inverter, battery enclosure, generator pad, any flanged inlet box on a wall), then the panel directory, garage and basement. Open every unexplained box on an exterior wall. Ask the customer the scripted question: "Is there anything that can power this house when the utility is off, including anything you plug in?" Acceptance: every source found is on the list with its location. Wrong looks like a label on the panel referencing equipment you cannot find, or an interlock kit on a breaker with nothing apparently connected; stop and find it before going further. Hazard: keep hands off every disconnect during the survey; you are reading, not operating.

3. Read the posted sequence and the placards. Installations under NEC Articles 690, 705 and 706 (in the edition your jurisdiction adopted) are required to carry placards identifying sources and their disconnects, and many battery systems post a shutdown order. Acceptance: you can name each source's disconnect and the opening order. Wrong looks like placards that disagree with what you found; treat a placard as a lead, not as truth, and if a battery's sequence is missing, call the installer before isolating it. Hazard: do not open the battery enclosure to find a hidden switch; the cells stay energized whatever any switch says.

4. Isolate the generator first, so nothing starts when you remove the others. For a standby unit, set its controller to OFF (not AUTO), then open its output breaker, then disable its start by the manufacturer's method (often removing the control fuse or disconnecting its starting battery). For a portable, confirm it is not running, unplug the cord from the inlet, and set the generator breaker in the panel to OFF. Acceptance: controller reads OFF, output breaker open, cord out of the inlet. Wrong looks like a controller that will not stay in OFF or an inlet with a cord you cannot trace; stop and resolve before step 5. Hazard: a standby unit in AUTO can start without warning when the ATS sees utility loss, so keep hands clear of the enclosure until the controller is OFF, and never start any engine to test something during this procedure (carbon monoxide).

5. Isolate the battery and the solar by their own methods, in the posted order. Absent a posted order, initiate rapid shutdown, open the PV AC disconnect, then shut the battery system down by its own switch or software command and open its AC disconnect. Acceptance: each disconnect visibly open, the battery's status display (if it has one) reading off or standby, and rapid shutdown initiated. Wrong looks like a battery display still reporting backup power, or a disconnect handle that moves but does not show open; stop and call the installer. Hazard: in daylight the PV conductors between the modules and the rapid shutdown devices remain energized whatever the AC side shows, and the battery cells remain energized always, so you work downstream of these disconnects only, never on the array or battery side of them.

6. Open the utility main last, and tell the household before you do. Say out loud, to every adult present, that the power is about to go off on purpose and nobody is to start, plug in or switch on anything. Then open the main. Acceptance: main handle in the open position, the household warned by name. Wrong looks like the lights staying on in part of the house; that is a source still feeding a section, so stop and go back to step 2. Hazard: the line side of the main breaker and the meter base stay energized from the utility; nothing in this procedure makes them safe to touch.

7. Apply a lock and tag to each disconnect you opened. One lock per source where the device accepts one (29 CFR 1910.333(b)(2) in general industry, 29 CFR 1926.417 on construction work), one tag on every device, each tag carrying name, date, time and phone number. Post a summary notice at the main panel listing every source and its disconnect location. Acceptance: tag count equals source count on your list. Wrong looks like a device that will not take a lock; tag it and have the helper keep watch. Hazard: a tag alone does not stop an app, so ask the customer to put their phone down on the system app and to not change settings until release.

8. Prove dead at the point of work with live-dead-live. Test your meter on a known live source (a proving unit, or the line side of the main, which stays live). Test every conductor combination at the work point: each ungrounded conductor to neutral, to ground and to each other. Re-prove the meter on the known source. This sequence is from NFPA 70E-2021, 120.5. Acceptance: under 1 volt on every combination, with a good proof before and after. Wrong looks like any reading of line voltage, or a reading that rises and falls; stop, step back from the work point and treat it as an unlisted source. Hazard: you are testing a conductor you have not yet proven dead, so wear the voltage-rated gloves and eye protection your arc-flash assessment calls for, and test from a stable position.

9. Do the work, then restore in the reverse order of risk. Remove tools and confirm covers are on. Close the utility main first. Wait for the grid-tied inverter to reconnect, commonly about five minutes under its anti-islanding settings, then close the PV disconnect. Restore the battery by its posted startup sequence. Return the generator: control fuse or battery back in, output breaker closed, controller to AUTO, or the portable cord left disconnected as the customer prefers. Acceptance: each source shows normal status, the controller reads AUTO, every tag removed by the person who applied it, and the customer confirms their app reads normal. Wrong looks like a fault code at restart; photograph it and call the installer rather than cycling it repeatedly, and do not leave a customer whose battery will not return to normal. Hazard: closing the main re-energizes everything downstream at once, so call "power coming on" first and keep the panel cover on.

The record this produces

The job record carries: the source list from step 1 and the corrected list from step 2, each disconnect location, open and close times, the meter and its proof readings, the dead-test readings, tags applied, any placard discrepancy, and any source added during the job. It lands on the ticket with a photo of each opened disconnect. It is read by the next tech at this address, the installer if the system faults after restart, and the owner if anything goes wrong. An added source goes into the address notes too, so step 1 finds it next time.

A worked pass: the source nobody listed

A lead tech and a helper are replacing a failed 20-amp breaker and its damaged receptacle on a kitchen circuit, which lives in a backed-up-loads subpanel.

• Step 1: Permits show utility, a string-inverter PV system with rapid shutdown, a home battery, and a standby generator with ATS. Four sources on the ticket.
• Step 2: Survey finds all four. The customer, asked the scripted question, says "just those". The tech notes a small flanged box on the garage's side wall with a weathered cover and assumes it is a low-voltage junction. Nobody opens it. This is the miss.
• Steps 3 to 7: Generator controller OFF, output breaker open, control fuse pulled. Rapid shutdown initiated, PV AC disconnect open, battery shut down by its switch, display reading standby. Household warned, main opened at 10:42. Four locks, four tags, notice posted. Tag count 4, source count 4.
• Step 8: FAILS. Meter proven on the line side of the main at 241 volts. At the subpanel, the kitchen breaker's load terminal to neutral reads 121 volts. The stop rule applies: the tech steps back, removes nothing, and calls the helper over.

The trace takes about 15 minutes. The subpanel carries a second breaker with an interlock plate, labeled in faded marker "GEN". It is closed. The garage box is a generator inlet the previous owner installed. The customer's spouse, hearing the house go dark at 10:42 and used to outages, went to the garage and started the portable generator kept there for exactly this, plugged into that inlet.

The fix inside the procedure: the spouse shuts the generator off; the tech unplugs the cord, opens the GEN breaker, adds a fifth tag and lock, updates the notice and the source list to five. Step 8 re-run: meter proven at 241 volts, every combination at the work point under 1 volt, re-proven at 241 volts. Work proceeds.

Why it was caught: the survey finds what you can see; the dead test finds what you could not. A tech who treated four tags for four sources as finished, and skipped the test because the house was "obviously" dark, would have been working on 121 volts. Note also that step 6's warning was given but did not name the generator, because nobody knew it existed; the warning only covers the sources on the list.

The record: five sources, the inlet photographed with its location, a note that household members start the portable during outages, and the address notes updated so the next visit lists five at step 1.

References

• NFPA 70E-2021, 120.5: process for verifying an electrically safe work condition, including the before-and-after meter proof.
• 29 CFR 1910.333(b)(2): lockout and tagging for electrical work in general industry; 29 CFR 1926.417 is the construction-side counterpart for circuits.
• NFPA 70 (National Electrical Code), Articles 690, 702, 705 and 706, in the edition your jurisdiction adopted: PV, optional standby, interconnected sources and energy storage placarding and disconnects.
• See related: Homes with Solar, Batteries or Generators Already Installed.
• See related: Off-Grid and Battery-Backed Homes.