Solar Arrays for Every Trade: What Stays Live in Daylight

Why this matters

A gutter installer, a painter on a ladder, an HVAC tech running a new lineset up the side of the house: all of them end up within arm's reach of solar wiring that nobody on their crew owns. The common belief is that someone flipped a switch and the system is off. On most roofs that is only partly true, and the part that stays live is the part you are standing next to. This card tells you which part that is, how to read the labels that say so, and what you never do to a module or a rooftop conduit.

For the system's components and how it ties into the house, see related: Solar PV Basics for Trade Service Reference. This card is only about what is energized when, and why.

Why a module is never "off" in daylight

A solar module is a set of cells wired in series. Each cell makes a voltage whenever light reaches it. There is no switch inside the module, and nothing upstream can tell the cells to stop.

Voltage arrives with very little light. A module's open-circuit voltage (Voc, the voltage with nothing connected) climbs close to its full value at dawn, under heavy overcast, and in the shade of a tree. What scales with sunlight is current. So "it's cloudy, the panels aren't doing much" is true of the power and false of the shock.

Cold raises it further. Voc goes up as the cells get colder. A string's highest voltage shows up on a bright, cold morning, not a hot afternoon.

Series adds it up. On a string-inverter system, modules are wired end to end and their voltages add. Read the module's own label for its Voc. Say a roof carries one string of 12 modules whose labels each read 40 V open circuit (illustrative; read the real label). That string sits at 12 x 40 = 480 V DC with nothing connected, before any cold-weather rise. NEC 690.7, as adopted, caps that maximum at 600 V on one- and two-family dwellings, which tells you the ceiling a residential roof is designed up to.

DC does not let go. Household AC passes through zero volts 120 times a second, which helps an arc go out. DC never crosses zero. A nicked DC conductor or a connector pulled apart under load can draw a sustained arc that keeps burning and can start a fire in the roof deck.

What rapid shutdown does, and what it does not

Rapid shutdown is a code requirement, NEC 690.12, that lets anyone (usually a firefighter) drop the voltage on the system's wiring from the ground. It arrived in the 2014 NEC and was rewritten in the 2017 edition; what you find depends on which edition your jurisdiction had adopted when that roof was permitted.

The 2017 edition onward, in substance: conductors outside the array boundary, which is defined as one foot from the array in all directions, must drop to 30 V or less within 30 seconds of the shutdown being started. Conductors inside the boundary must also be controlled, and the 2017 edition gives several ways to do it, the common one being module-level electronics that hold each module's output at 80 V or less within 30 seconds. Check the current edition for the exact options.

The 2014 edition: only the conductors more than 10 ft from the array (or more than 5 ft inside the building) had to drop to 30 V within 10 seconds. Everything on the roof could stay at full string voltage.

Before 2014: no rapid shutdown at all. Hitting the AC disconnect stops the inverter making AC; every DC conductor from the modules to the inverter stays at string voltage in daylight.

What rapid shutdown never does, under any edition:

• It does not stop the cells. A module-level device limits what leaves the module. The cells, the module's internal wiring and its junction box are still making voltage.
• It does not touch a battery. A battery's own terminals are live whatever any switch says. See related: Home Battery Systems for the Trades That Share Their Wall.
• It is not a lockout. A rapid shutdown switch is a convenience for an emergency. It is not a point anyone but the owning trade isolates and tags for work on the system.
• It does not prove itself. A failed module-level device, or a system installed under an older edition, gives no warning at the switch. You cannot see from the ground whether the roof obeyed.

Reading the labels

Rapid shutdown systems carry a label at the service equipment, or where the switch is, that tells you which kind of system you have. NEC 690.56(C), as adopted, sets the wording, the colors and the layout; the mock below gives the two 2017 versions in substance. Check the label on the actual house, not this card.

AT THE METER OR MAIN PANEL (version A):
  SOLAR PV SYSTEM IS EQUIPPED WITH RAPID SHUTDOWN.
  TURN RAPID SHUTDOWN SWITCH TO THE "OFF" POSITION
  TO SHUT DOWN PV SYSTEM AND REDUCE SHOCK HAZARD
  IN THE ARRAY.
  -> module-level controls; array AND wiring reduced

AT THE METER OR MAIN PANEL (version B):
  SOLAR PV SYSTEM IS EQUIPPED WITH RAPID SHUTDOWN.
  TURN RAPID SHUTDOWN SWITCH TO THE "OFF" POSITION
  TO SHUT DOWN CONDUCTORS OUTSIDE THE ARRAY.
  CONDUCTORS WITHIN THE ARRAY REMAIN ENERGIZED
  IN SUNLIGHT.
  -> only wiring past 1 ft from the array reduced

AT THE SWITCH:
  RAPID SHUTDOWN SWITCH FOR SOLAR PV SYSTEM

ON CONDUIT, RACEWAY, JUNCTION BOXES:
  PHOTOVOLTAIC POWER SOURCE
  -> DC from the modules, repeated along the run

Version B is the one to stop on. It is the label telling you in plain words that the roof stays live with the switch off.

The conduit label means DC from the array. NEC 690.31, as adopted, has that DC wiring marked along its length (every 10 ft in the 2017 edition, check yours). On a wall, an attic rafter or a roof, a "PHOTOVOLTAIC POWER SOURCE" marking means you are looking at the conductors running from the modules toward the inverter.

No label is information too. An older system may simply have none, or the label may have faded off. Treat an unlabeled system as having no rapid shutdown at all.

Why nobody steps on a module

A module is a sheet of tempered glass over thin silicon cells, bonded to a backsheet, in an aluminum frame. It is built for snow load spread evenly, not a boot heel.

• Cells crack where you cannot see. Weight on the glass flexes it and cracks the cells underneath. The glass can look perfect. A cracked cell loses output and can run hot (a hot spot), which over time can scorch the backsheet.
• The glass is slick. Wet, frosted, dusty or covered with pollen, module glass gives almost no grip, on a surface already pitched like the roof.
• The backsheet and the wiring are under it. A knee through the glass reaches live parts.

Set nothing on a module either: not a bundle of shingles, not a tool bag, not a ladder. Ladders go where the array is not, against the wall or on a standoff rather than on the gutter itself, and never on a module or its frame.

Why nobody cuts rooftop conduit

A conduit or raceway leaving the array is carrying DC from a string, or AC from microinverters, or both. You cannot tell which from the outside, and you cannot tell whether rapid shutdown has worked on it.

• Cutting, drilling, or bending it is the arc. A saw blade, a drill bit or a pry bar that reaches the conductors under string voltage can start a DC arc in your hand.
• Unstrapping it moves the connectors. Many runs carry plug-together DC connectors in junction boxes or under the array. Pulling a run sideways to fit a gutter or a lineset can separate one under load.
• "Temporarily" is the problem. A run moved out of the way and refastened by a non-solar trade has no inspection behind it.

If the run is in your way, it is the solar contractor's run to move. See related: How to Work on a Roof That Carries Solar Panels for planning that around your job.

Worked example: the gutter under the array

A gutter crew is replacing 40 ft of gutter on the south eave. The array sits two courses up from the eave, so the bottom row of modules is about 3 ft above the gutter line. A conduit leaves the array's east end, runs down the roof, over the eave and down the wall to an inverter in the garage.

Read the label first. At the meter, the crew lead finds version B: rapid shutdown, conductors in the array remain energized in sunlight. So this is a 2017-or-later system with controls on the wiring leaving the array and not on the modules.

Work out what the switch changes. With the rapid shutdown switch turned off:

• The conduit on the wall is outside the array boundary (more than 1 ft from the array). It should be at 30 V or less within 30 seconds.
• The bottom row of modules, their leads and any connectors under them are inside the boundary and stay at string voltage in daylight.
• The gutter line is 3 ft from the bottom row, which puts the gutter work outside the boundary. The 1 ft margin ends 2 ft above the gutter.

What that means for the crew. Working the gutter itself puts them no closer than 3 ft to the array. Reaching up to clear leaves from under the bottom row is reaching into the boundary, toward wiring the switch did not touch, so nobody does it. The conduit crossing the eave sits exactly where the new gutter hangers go; the crew does not fasten a hanger through it, beside it or under its strap, and it does not get lifted to slide the gutter under. They leave a gap in the hanger spacing at the crossing and call the solar contractor about adding support there.

Who turns the switch. The crew does not turn the rapid shutdown switch off to "make it safe". Off, it stops production and the customer's monitoring may report a fault; and for this crew it changes nothing they are allowed to touch anyway. Their protection is distance and leaving the run alone.

What would change the call.

• Version A label, or microinverters under each module. The module outputs drop to a controlled level too, but the cells are still live. The hands-off rule for anything under the array stays exactly the same.
• No label at all. Assume a pre-2014 system: the conduit on the wall is at full string voltage in daylight whatever the switch does. The crew works the gutter, gives that run the same clearance as a live service drop, and calls the solar contractor before anything near it moves.
• Bottom row within 1 ft of the gutter. Now the gutter itself is inside the boundary, and this is no longer a gutter job the crew can do alone. It needs the solar contractor on site, or modules removed first.

The failure mode. The common one is not a shock on day one. It is a hanger screw driven through the conduit's strap and grazing the raceway, or a run pried out of its strap and set back loose. It passes for months, then a connector works apart in the wind and arcs under the array.

What to say when you call

Tell the solar contractor, or the customer to pass on: which label you found and its exact words, where the run you need to work near is, how far it sits from the array, and what your job needs (a gutter hanger at that spot, a lineset route, a wall to paint behind the run). "Version B label, conduit crosses the eave 6 ft from the east corner, we need a hanger there" gets a plan. "There's solar in the way" gets a callback. See related: Describing a Problem in Another Trade's Own Words.

If a module is cracked, a run is loose, or a connector is hanging, do not touch it. Photograph it from where you stand and hand it off; see related: How to Hand Off a Problem You Found in Another Trade's System.

References

• NFPA 70, National Electrical Code, Article 690 (690.7, 690.12, 690.31, 690.56), in the edition your jurisdiction has adopted; rapid shutdown requirements differ between the 2014 and 2017 editions
• See related: Solar PV Basics for Trade Service Reference
• See related: Homes with Solar, Batteries or Generators Already Installed
• See related: How to Work on a Roof That Carries Solar Panels
• See related: The Five Questions to Ask About a System That Is Not Yours