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NEMA/NFPA/UL LVDC Conference

April 8, 2011

Product Standards

Ken BoyceUnderwriters Laboratories Inc.

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• DC equipment has been used in many focused applications in the past, dating back to Thomas Edison as a vocal proponent

• Product standards & codes have addressed these focused applications, with much evolution

LVDC standards development

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“Farm Lighting Plants”

• 1905 NEC contained requirements for Direct Current systems; “Low Potential” was specified as 550 Volts

Source: powerstream.com

• 1920 NEC, Rule 43B addressed “Isolated Light and Power Equipments for Less Than 50 Volts”

• This grew into Art. 720 by the 1953 NEC, which addressed circuits such as “farm lighting plants” operating at about 32V

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Today

• Much has changed since the early days of DC power distribution…

• but today we see elevated interest in DC distribution based on a variety of factors.

• This produces the need for codes & standards to adequately address them

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LVDC Systems

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Generation

• DC distributed generation sources use is expanding

• Typical sources are photovoltaic (PV); some increase in use of fuel cells

• DC power supplies & batteries used in specific equipment applications

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Photovoltaic systems

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Photovoltaic systems

• Photovoltaic systems typically generate (& distribute) DC power on premises

• Modules may or may not be “low voltage” - ~0.5V/cell

• Increasing voltage means more attention to mitigating hazards such as shock, ground faults and arcing

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Variations in PV systems

• Module outputs vary based on design, number of cells and technology

• Crystalline modules up to ~36V; Thin film modules up to ~80V

• System operating voltage varies based on number of modules, application & configuration

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PV Requirements

• Installation addressed by NEC Art. 690

• UL has developed a suite of publications to address PV equipment and related wiring/distribution devices

• UL 1703 the primary standard for PV

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PV Experiences & Learnings

• System voltages trending upward

• Special consideration for standards is needed

• Efforts underway to standardize connector & module port configurations

• Ground faults not unusual based on wiring practices

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Fuel Cells

Fuel Cells addressed by a number of standards: Source: www.slipperybrick.com

•Stationary: ANSI FC-1•Portable: ANSI FC-3•Hand-held: UL Sub 2265A•Industrial Trucks: ANSI/UL 2267

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Storage

• Storage may take many forms

• In practicality, today it’s typically accomplished through batteries

• Batteries expected to remain the primary storage technology for the near future

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Battery Standards

• Stationary: UL 1973

• Vehicle: UL 2580 (and others) – relevant for V2G & plans to repurpose auto batteries for second life

• Portable & cells – many standards including UL 1642 Lithium, UL 2054 Household, UL 2575 Battery Systems for Appliances

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Storage issues moving forward• Developing/refreshing codes and

standards as needed – e.g. V2G

• Addressing safety of evolving technology as well as concerns like relative performance

• Repurposing and other practical use issues

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Distribution

• Standards may be needed to address unique aspects of DC distribution

• New use for existing products or new requirements and products?

• PV platform includes Sub 4703, Subs 6703/6703A, Sub 2759, Sub 4248-18, and Sub 98B

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Grid issues

• Grid connectivity a primary concern addressed by UL 1741 and IEEE 1547

• Much effort dedicated to standards for smart grid use to enable more sophisticated use and distribution

• Efforts also underway to develop standards for microgrids to maximize power distribution on campuses

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Electric Vehicle Supply Equipment

• UL has been active in developing EVSE safety standards, including Sub 2594

• Addresses a critical concern for distributing DC to the point of use

• Special protective measures to mitigate user access and electric shock concerns

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Use

DC presently used in many places:

•Lighting•Information technology (IT) rooms•Photovoltaic systems

…..and many more are on the horizon

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Lighting

• Low voltage lighting systems addressed by UL 2108 and NEC Article 411

Source: www.lightsoutlighting.com

• LED Lighting addressed by UL Sub 8750 and other standards

Source: www.lightsoutlighting.com

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Suspended ceiling grid LV lighting

• Recently Listed by UL to Sub 2577

• Originally envisioned for lighting and other equipment (e.g. hot spots)

• Presently limited to use in lighting applications based on NEC Article 411 provisions

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Ceiling Grid DC System

Source: www.armstrong.com

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Movement to more DC distribution

• The ceiling grid concept showed movement to establishing an LVDC grid within a premises

• We have seen other product concepts with similar approaches

• Product standard and Code issues both come into play

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Focus on components and materialsUL working to address component requirements specific to DC issues:

•Research work on characterization of polymers to DC sources (up to 1kV) based on potential for different response to DC than AC•Components such as DC appliance couplers for data centers

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Materials

• Polymers extensively assessed for reaction to AC conditions

• Reaction to DC use may be different

• UL reviewing issues such as tests for DC tracking resistance and resistance to arcing from DC

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Couplers for DC Data Centers

•Variety of designs

•Being addressed by development of UL Sub 2695 and IEC 62695

•Ratings up to 400Vdc

Source: The Green Grid

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On the horizon

• Increasing community/local energy storage, DC generation and DC distribution within premises

• Increasing issues with infrastructure for DC distribution

• Need product standard & Codes to address key issues such as safety, interconnection, and interoperability

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Standards development

• Many organizations active in developing standards to address the phenomenon of DC distribution

• These organizations include UL, NFPA, IEEE, IEC, EMerge Alliance, Solar ABCs

• Holistic efforts needed to address key issues for the public, including safety

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Conclusion

• Products standards & codes address focused LVDC applications and new uses

• Standards development will be required to address key issues such as safety, interconnectivity, and interoperability

• Collaboration by key stakeholders is needed to generate a cohesive set of standards & codes supporting safe deployment

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Thank you

Kenneth.p.boyce@us.ul.com847.664.2318