Solar Panel Safety

Solar panels have one property that makes them different from almost every other electrical component in a building: there is no off switch. A panel produces voltage whenever light falls on it. You cannot de-energize it, only cover it.

That single fact drives most of what follows.

An array is always live

A panel in daylight is generating. Even under heavy cloud, at dusk, or lit by a worklight, it produces reduced but real voltage. Open-circuit voltage, the voltage present when nothing is drawing current, is at its highest with no load connected, which is precisely the condition you create when you disconnect something to work on it.

Voltage adds in series. A single panel might produce 20 to 40 volts open-circuit. Six wired in series produce well over 100 volts DC, and larger strings go considerably higher. That is firmly in the range that can kill.

Practical consequences:

• Cover panels with opaque material before working on array wiring. Cardboard or a tarp works; a thin cloth may not.
• Assume every conductor is live unless you have measured it yourself, at that moment.
• Work in pairs on anything above about 60 volts DC, so someone can disconnect and call for help.

DC arcs behave differently from AC arcs

This is the part people underestimate.

Alternating current passes through zero volts twice per cycle, 100 or 120 times a second. Any arc that forms has a natural opportunity to extinguish at each of those crossings, which is what makes ordinary AC switches feasible.

Direct current never crosses zero. Once a DC arc establishes, nothing interrupts it naturally. It sustains itself, burns extremely hot, and can continue until the circuit is physically broken or the conductors are consumed.

This is why:

• Switches and breakers must be DC-rated. An AC-rated device used on a DC circuit may not be able to break the arc it creates, and can fail while appearing to be “off.” Its voltage rating must also cover the string’s cold open-circuit voltage.
• Loose connections are a fire risk, not just an efficiency problem. A high-resistance joint under load can develop into a sustained arc.
• Never disconnect a live DC circuit under load. Break the load first, then the circuit.

Connectors

Modern arrays use purpose-built photovoltaic connectors, MC4 being the common standard. Some rules that are routinely ignored:

• Do not mix brands. Connectors that physically mate are not necessarily compatible, because differing tolerances and materials produce joints that overheat. Same manufacturer on both halves.
• Crimp with the correct tool. Pliers do not produce a gas-tight crimp, and a bad crimp is a future hot spot.
• Seat them fully. A properly mated connector clicks and cannot be pulled apart by hand.
• Do not use them as switches. They are not rated to break current under load and will arc.

Roof work

For most people building an off-grid or backup system, the largest genuine risk is not electrical at all. It is the fall.

Falls from roofs cause more serious injuries in solar installation than electricity does, by a wide margin. If you are working at height, that is where your caution belongs: proper anchorage, a harness, appropriate footwear, and not working alone.

Panels are also awkward to handle: large, rigid, and effective sails in wind. A gust while carrying a panel on a roof is a realistic and serious hazard. Do not move panels in wind.

Ground mounts and other physical risks

Ground-mounted arrays remove the fall hazard and introduce others: the structure must resist wind uplift, which is substantial on a large flat surface, and frames must be properly grounded.

Glass breakage matters more than people expect. A broken panel may still be generating, and now has exposed conductive material and sharp edges. Cover it, then deal with it.

Panels also get hot. A dark surface in full sun reaches temperatures that will burn on contact.

Grounding and bonding

Array frames and mounting structures need to be bonded and grounded properly. This does two things: it gives fault current a defined path so protective devices operate, and it reduces shock hazard from a frame that has become energized through insulation failure.

Grounding requirements are specific, code-driven, and vary by jurisdiction and system type. Our wiring content follows the NEC (NFPA 70). This is an area where getting it approximately right is not good enough, and where an inspection requirement usually exists for a reason.

Before you start work

• Cover the panels.
• Confirm the DC disconnect is open, and verify with a meter rather than trusting the label.
• Measure before touching. Every time.
• Use insulated tools and remove metal jewellery.
• Have someone with you for anything above roughly 60 volts DC or above ground level.

Scope

This page covers hazards and general practice, not code compliance. Permanently installed photovoltaic systems are subject to real electrical code requirements (NEC Article 690 in the United States), and most jurisdictions require permits and inspection for anything attached to a building or connected to its wiring.

If your system will interact with utility service in any way, the requirements are stricter still, and that is a job for a licensed installer rather than a weekend.