Early in the field of electrical development and distribution, three superstars in technology and trade—Nikola Tesla, George Westinghouse, and Thomas Edison—were locked in a battle for supremacy on whether AC or DC should be the prevailing current. While each camp had a strong argument about which electrical current was safer, in reality, regarding electrical shock or the subsequent propagation of flame, each type of the aforementioned electrical currents must be treated with care.
New technologies of pulsed DC current generation are currently being explored with claims of increased safety for users, along with the potential for lessening installation practices and the need for municipal electrical inspections. One of the new power technologies offered recently is the exciting field of Class 4 fault-managed power systems (FMPS), which will impact the lighting field by potentially unlocking the previous limitations imposed on Class 2 circuits. The 2023 edition of NFPA 70, the National Electrical Code, now has a new Article 726, addressing Class 4 FMPS produced by various manufacturers.
So, what is so unique about Class 4 FMPS, and why should we become knowledgeable of the intricacies of this new technology? Let’s take a birds-eye view of this new and promising technology that Tesla, Westinghouse, and Edison could have never dreamed up.
To better explain Class 4 FMPS, we need to review the limitations of a Class 2 power system. Class 2 power supplies are limited by either impedance or having a fuse or resettable circuit breaker that does not allow the short-circuit current to exceed 8 amperes after one minute. Most Class 2 lighting systems, therefore, are limited to 100 volt-amperes and less than 42.4 volts peak, 30 volts RMS, or 60 volts DC. Furthermore, the distance from the power supply to the lighting product is limited by the secondary wire gauge used.
“The magic occurs in the claim that any shock hazard fault will shut down the circuit as the transmitter and receiver are in constant communication with each other”
Class 4 systems, which use a pulsed or digital DC current, are allowed to be a maximum of 450 volts, and due to the circuit use special Class 4 cables that can be run thousands of feet. A Class 4 system typically comprises a transmitter that is connected to line voltage then interconnected with special power/communication cable to the Class 4 receiver, which may or may not be wired to the lighting product or other Power over Ethernet or information technology product.
Underwriters Laboratories (UL) has a published UL 1400-1: UL LLC Outline of Investigation for Fault-Managed Power Systems – Part 1: Safety Requirements and UL 1400-2: UL LLC Outline of Investigation for Fault-Managed Power Systems – Part 2: Requirements for Cables. It should be noted that the UL Outline of Investigation is not an ANSI standard, which means that the requirements may be upgraded and/or revised at a later date.
So, where is the magic in a Class 4 system? The magic occurs in the claim that any shock hazard fault will shut down the circuit as the transmitter and receiver are in constant communication with each other. The test signal is reported to be sent back and forth (typically, 500 times per second) through the cable such that a fault will be detected and open the circuit within milliseconds.
Class 4 technology looks extremely promising as manufacturers’ literature lays out the benefits and features such as:
Its ease of installation, as the product is installed similarly to IT installation practices now used.
Enhanced safety, as the circuitry detects potential fault conditions at which point the power will be reduced quickly to prevent an electrical shock.
Under fault conditions, the reduced power will lessen the chance of propagation of flame to start a fire.
The Class 2 limitations of power can be surpassed due to the redundancy of the safety circuit, which has a fast response time to lessen power.
Using the Class 4 cabling allows for longer runs of cable without compromising performance.
Municipalities may wave installation inspections decreasing installation time.
Class 4 systems can be easily integrated into energy-savings initiatives, reducing energy consumption for sustainable building designs.
As with any new technology field, experience will be pivotal to ascertain if the claims made are valid and protect users from harm. Class 4 systems are currently intended to be used in sports stadiums and arenas, office buildings, airports and passenger terminals, manufacturing facilities, wireless access points, routers and servers, and smart displays/digital signage.
A “Safety” column update will follow with further information in the future as field experience is gained with the Class 4 systems. Additionally, local municipalities may opt to require appropriate electrical inspections until actual installations prove otherwise.
The development and implementation of Class 4 power is exciting, and many of the shortcomings using Class 2 power are mitigated. There will be arguments for and against using this new technology just like when Tesla and Westinghouse supported AC power, while Edison backed DC power. As history tells us, both AC and DC have their place; Class 4 should prove to be an asset as we seek to conserve energy.
Finally, congratulations to both the National Fire Prevention Association Code Making Panel and UL for reacting expeditiously so that the new technology can move forward without delays due to a lack of requirements.
Jerry Plank, LC, is the CEO/founder of Wilger Testing, an accredited third-party laboratory testing for product safety and performance.
