December 6, 2022 – Enclosed drives are estimated to represent between 45-55% of the total drives market worldwide. While NEMA 1 (IP21) drives constitute the majority, others include NEMA 12 (IP54), NEMA 4 (IP65) and NEMA 3R (IP27) versions. Many are for new installations, but many others are used in retrofit installations ranging from across-the-line start to VFD (variable-frequency drive) control.

NEMA 1 and UL Type 1 are the enclosure ratings according to NEMA 250 and UL 50/50E standards, respectively, for the indoor use of an electrical equipment—in our case, enclosed adjustable-speed drives.

NEMA 250 is an ANSI standard used for self-declaration of enclosure Type ratings e.g. NEMA 1. UL 50/50E are UL and CSA harmonized ANSI standards. However, unlike NEMA enclosure ratings according to NEMA 250, testing and certification by UL (or similar certification agency) is required to mark electrical equipment with an enclosure rating of, say, UL Type 1 (according to UL 50/50E).

To ensure electrical and fire safety, UL-listed electrical equipment intended to be used indoors requires a minimum enclosure rating of UL Type 1 to comply with listing requirements and ensure acceptability by the authority having jurisdiction (AHJ), according to the CE Code or local applicable electrical codes and regulations.

The NEMA rating is self-certifying, which means the rating hinges upon the manufacturer’s compliance with published standards for enclosure protection.

By contrast, for “UL Type 1” listings, rigorous certification/compliance testing must be conducted against a rigid protocol of protection testing by the third party, whether for indoor or outdoor application.

In short, this is why the NEMA enclosure rating does not equate to the apparently similar UL enclosure rating, whereas products with the UL rating do, in fact, meet or exceed all relevant requirements of the NEMA specification for use in North American industrial and building markets.

The testing is performed not only to UL enclosure standards (UL 50/50E), but also the new standard UL 61800-5-1, which recently replaced UL 508C for variable frequency drives with respect to electrical, thermal and energy safety considerations.

Such drives are typically found on centrifugal pumps, radial/axial fans, compressors, screw pumps, hydraulic pumps, dosing pumps, and all manner of conveying equipment—plus hoists and cranes, printing presses, and so much more—in both continuous and discontinuous motion applications.

Commercial building applications for UL-listed drives and enclosures are also numerous, ranging from high-rise motor control centres (MCCs) to plenums for HVAC and lighting control.

Why is an enclosure/kit required for open drives?

For an open-type (IP20) drive, protection must be provided against direct or indirect contact of hazardous parts—as well as electrical, thermal and energy hazards in use—to ensure product and personnel safety, and avoid property damage from a potential fire hazard. Manufacturers routinely provide either a standard approved enclosure or an adapter kit for the attachment of conduit, connectors and other hardware.

In retrofit applications, there is typically no space in an existing enclosure for the additional hardware required. This additional hardware depends on the end application requirements, and could include control components such as terminal blocks, relays, DC power supplies, PLC, etc. This is especially germane when, as part of the retrofit, traditional electromechanical controls are being replaced with VFDs, where something must be mounted external to the enclosure or MCC. In such cases, a new rating distinction must be considered essential.

Whether the enclosure is stationary or portable (as might be found in a process industry location, such as oil field operations), it is often necessary to mount the drive separately (from the other controls, power supply, PLC) in a new machine or mobile electrical power unit. This facilitates easier maintenance but, in such cases, the additional protection level of the UL Type 1 standard becomes critical.

Kits are provided to comply with relevant electrical codes and regulations for the installation and wiring of IP20 open-type drives. These UL enclosure/kit ratings (UL Type 1, 12, 3R, etc.) guide the construction and performance in accordance with UL 50/50E + End Product Standard.

The certification process requires that the design be thoroughly evaluated and additionally tested by a third party. When a kit is deemed to be UL Type 1, it provides users the following:

• Design per UL 50 and UL 50E, plus UL 61800-5-1 for drives.
• Comprehensive independent third-party testing.
• UL Listed “Open/IP20” drive and UL Type 1 Kit compliance.

What to look out for in available kits

Most of the enclosure kits currently available in the market are rated “NEMA Type 1 or NEMA 1” only and are not “UL Type 1,” meaning they do not comply with UL/NEC specifications. It is suggested that checking the drives supplier is advisable to determine the UL listings applicable on their kits and NEC compliant installation.

Also, some kits available on the market are tested and listed according to the old UL standard for drives, namely UL508C; however, they are not rated according to the latest and current drive standard UL 61800-5-1. For future installations, specifiers and contractors should look to assure that the components they are installing will meet these new standards and allow for better compliance to the new testing requirements and regulations.

Why is there a new drive standard UL 61800-5-1?

The new standard calls out more stringent construction and performance (testing) requirements as compared to UL 508C, which have been imposed by the UL to ensure a higher level of product safety.

Short-circuit (SC) tests are now done at standardized amperages (5, 10, 18, 42 kA, etc.) as well as high fault currents (65 kA, 100 kA, etc.) on all output terminals—including DC terminals available to the customer (not just motor terminals).

Various breakdown-of-component tests by simulating component failures within the drive are also conducted to standard, as well as high fault currents to assure these enclosures meet the higher product safety requirements.

Not synonymous

For the maximum protection of property, equipment and personnel, it is highly advisable to consider the differences between the NEMA 1 and UL Type 1 enclosures for low-voltage electric drives. These ratings are not synonymous, and the independent lab testing done by a third-party to UL standards has substantial merit when sourcing products for a variety of new construction, new equipment and retrofit upgrades—both indoor and outdoor, stationary and mobile.

A senior member of IEEE, Nikunj Shah is responsible for the development and certification of low-voltage drive products, as well as product management for Sinamics G120X drives. He is actively involved in the development and maintenance of various national and international standards, and represents Siemens in various standards technical panels, as well as many IEC and NEMA technical committees. He holds a Master’s Degree in Electrical and Computer Engineering, and has over 20 years of experience in the design, development and certification of converters and drives, and in their application.

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