High voltage DC does not forgive design shortcuts. Arcs sustain longer, heat rises faster, and switching duty must be engineered, not assumed. UL 98B and UL 98C exist to remove ambiguity. This guide explains the difference, when to use each, and how to select DC disconnects that meet NEC and IEC requirements for modern PV and energy storage projects.
The Role of DC Disconnects in PV and ESS
DC disconnects provide a visible and reliable means to isolate arrays, battery strings, and power conversion stages. They protect personnel during installation and maintenance and enable compliant commissioning and service.
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Typical locations
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PV string and combiner boxes
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DC isolators at inverters and PCS cabinets
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Battery racks and containerized ESS systems
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DC distribution in data centers and telecom
UL 98B vs UL 98C in Plain Language
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UL 98B covers disconnect switches for high voltage DC in energy storage systems. Typical in ESS battery racks, DC distribution, and hybrid power cabinets.
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UL 98C covers disconnect switches for photovoltaic DC circuits up to 1500 VDC. Typical in PV combiner, re-combiner, and inverter input isolation.
Both demand verified DC load break performance, arc control, and thermal stability at rated current and voltage.
How NEC Ties In
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NEC 690 requires PV system disconnects that are suitable for DC and located for safe service.
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NEC 706 covers ESS, including disconnecting means for battery subsystems and PCS.
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Coordinate with local AHJ on placement, visibility, and lockable off requirements.
Selection Criteria That Matter
Voltage class
600, 1000, and 1500 VDC are common PV and ESS levels. Verify the switch rating and duty at your system voltage.
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Load and duty
Confirm the DC breaking capacity at operating current with expected switching frequency.
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Poles and polarity
Match poles to series strings and grounding scheme. Many PV and ESS designs use 2 or 4 poles.
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Thermal performance
Low contact resistance and adequate heat dissipation are essential for continuous DC load.
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Arc management
Look for double break contact designs, magnetics, or arc chutes engineered for DC.
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Accessories and safety
Padlockable handles, door interlocks, and auxiliary contacts for status feedback and EMS integration.
Environmental and Mechanical Considerations
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NEMA 3R, 4, 4X or IP65, IP66 based on outdoor or coastal exposure
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UV and corrosion resistance on rooftops and containers
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Vibration tolerance for mobile or rail-adjacent sites
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Wide temperature range for desert or cold climate deployments
Common Architecture Examples
PV array to inverter input
UL 98C disconnect at the inverter DC input or at the combiner output. Select poles to match array configuration.
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Containerized ESS rack
UL 98B disconnect on each rack output and a system level isolation point near the PCS. Coordinate with NEC 706 and system EMS.
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Hybrid microgrid
Combination of UL 98B and UL 98C where PV and ESS share a DC bus. Consider AC or DC changeover where redundancy or maintenance bypass is required.
Checklist for Submittals and AHJ Review
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Cut sheets with UL 98B or UL 98C clearly shown
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Voltage and current ratings at the design point
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SCCR coordination data
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Environmental rating and handle type
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Installation drawings showing location and visibility
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Lockable off and interlock details
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Optional visible blade or indication if requested by AHJ
Where Telergon Fits
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UL 98C DC disconnects up to 1500 VDC for PV isolation at combiners and inverter inputs
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UL 98B DC disconnects for ESS racks and DC distribution
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Compact DC disconnects for containerized systems and rooftop space constraints
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NEMA 4X and IP66 handles for outdoor and coastal installs
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Accessories for auxiliary signaling and locked off maintenance
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FAQs
Is a UL 98C device acceptable in ESS?
Use UL 98B for battery and ESS circuits. Use UL 98C for PV circuits. For shared DC buses, match the device to its exact circuit function.
How many poles do I need for a floating array?
Most floating arrays use 2-pole switching. Grounded arrays and certain fault strategies may require 4-pole. Confirm with your protection scheme.
Do I need visible blade indication?
AHJs vary. Visible indication or verified open position improves safety and inspection speed. Telergon offers options to meet either approach.
Talk to Telergon USA about UL 98B and UL 98C selections, drawings, and submittals, or request a quote.