Safety Switches & Disconnects

Switching 600 Vdc

When photovoltaic panels convert the sun’s energy into electricity, the power generated is direct current (DC). Typically, the systems are designed with DC system voltages in the 400–600V range. This is much higher voltage than typically found in building systems. The higher voltage, when combined with the lack of a current sine wave with zero crossings, creates a number of challenges in wiring, particularly when switching circuits on and off.

DC circuits consist of two wires—a positive and a negative. In most PV systems, one of these wires is grounded (like a neutral in an AC system). Which of the two wires is grounded is specified by the solar panel manufacturer. The more common application is a negative ground, and the location of this bond is usually found at the inverter. Per the National Electrical CodeT (NECT) Section 690.5(A), only the current-carrying ungrounded conductor should be switched. Thus, in a negative-grounded system, only the positive wire is switched.

Unlike AC systems that possess a current sine wave with zero crossings, the interruption of higher voltage DC circuits requires an increased air gap to safely and quickly interrupt and break the arc. The increased gap is accomplished by wiring multiple poles of a single switch in series for safe arc interruption. All switch manufacturers require the use of multiple poles at 600 Vdc to maintain the ULT listing. For this reason, a switch should only be used to switch one circuit. The UL listing of these products does not permit multiple circuits to be switched by one switch. Eaton’s new offering of PV switches have multiple poles factory-wired, and they are approved for NEC Article 690 applications right from the box. Other manufacturers require the contractor to add jumpers to a two- or three-pole switch, add a neutral, and add labels to meet this requirement. For fusible switches, the new Eaton PV switch requires only one fuse per switch—saving the customer at least one fuse on each switch.

Eaton’s solar disconnect

Eaton Corporation is proud to offer a new line of solar disconnects that provide the best solution for switching solar PV circuits. This exciting new offering is the first UL 98 listed switch that is labeled as “suitable for NEC Article 690 photovoltaic applications per UL 1741 requirements.

Features include:

• Marked as suitable for NEC 690 PV applications up to 600 Vdc
• UL 98 listed
• All switches are single-pole and suitable for switching one circuit
• Clear polycarbonate deadfront to guard against accidental contact with live parts
• NEC 690.17–compliant labeling warning that the switch terminals may be energized in the open position
• NEC 690.14.(C) 2 required “PV System Disconnect” label included
• Isolated ground terminals (neutral) for grounded conductors
• Ground lug for equipment grounding conductor
• NEMAT 3R, 12 and 4X stainless enclosures
• Fusible and non-fusible configurations—Class R fuse clips standard
• Fuse clips are located on the center pole to ensure that both fuse clips are de-energized—meets NEC Article 690.16, which requires isolation of the fuse from all potential supply sources
• Available for Flex Center modifications (windows, pilot lights, 316 grade stainless, and so on)