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June 27, 2023
Maybe you've heard of Class 4 power systems when the NEC added a rating for them in early 2023, but then you thought to yourself: "That sounds just like Power over Ethernet! What's the difference?" The two definitely have their similarities, but let's pit the two of them against each other.
This article compares two options for distributing DC (direct current) power throughout a building, as well as two options for transmitting and receiving data to-and-from connected loads (i.e. lighting brightness or color temperature). The first option for doing so is Power over Ethernet (PoE), and the second option that we'll cover in this article is called a Class 4 power (CL4) system. Class 4 power systems are a new addition to the National Electrical Code, or NEC for short, and are also called Fault-Managed Power (FMP) systems.
We know that the energy efficiency of a commercial building matters. Not only does having a more efficient building reduce operating costs but, the more buildings that prioritize energy efficiency, the smaller our carbon footprint becomes as a society. In fact, buildings are estimated to be responsible for about 40% of primary energy use in the US, 72% of electricity consumption, and 39% of carbon emissions.
So what’s one of the most impactful things that can be done to make buildings more energy efficient? Well, first, the type of electricity being distributed throughout a building needs to be considered. There are two types of electricity: alternating current (AC) and direct current (DC). Currently, AC power is being delivered to our buildings from power lines. However, DC consumption makes up about 74% of the total energy load in buildings that have EV charging stations, and HVAC equipment with DC motors. This means that DC electrical loads in buildings with AC power distribution are not getting the type of electricity they require, and so they have to convert the AC power they get into the DC power they need. This is often an inefficient process, wasting about 20% of power consumed by a load.
Delivering DC power to DC electrical loads (such as LED lights) can therefore cut back on energy wasted by AC to DC conversions. To do this, one would use a DC power distribution system. Class 2 rated power systems, such as Power over Ethernet (PoE), have been popular as low-voltage DC power distribution systems in buildings. But, more recently, it looks like they are getting some competition from higher voltage DC systems. The 2023 version of the NEC introduced a rating for another type of DC power distribution system in Article 726: the Class 4 power system (or Fault-Managed Power system). UL has also recently released an outline of investigation (soon to be a standard) for Class 4 systems under UL 1400-1, and UL 1400-2. Class 4 power systems are similar to Power over Ethernet, but differ in some major ways. In this article, we’ll break down these differences.
All digital devices (that require semiconductors or batteries) require DC electricity, and our world is increasingly becoming more digital. So, consequently, the demand for DC power is increasing. These DC electrical systems and devices are also evolving. For example, battery storage systems for solar power, level 3 electric vehicle (EV) fast charging, variable frequency drive (VFD) HVAC systems, smart hubs and more, are all being developed, and used more often. As these DC devices and systems develop, they act as the tailwinds for the proliferation of DC power distribution. This is a major reason why it’s so appropriate that the NEC introduced a rating that promotes a new type of DC distribution system (the Class 4 rating). More and more of our building systems and devices are going DC, and it’s time for the electrical systems in our buildings to align with this change.
Power grids have distributed AC power since the Westinghouse Company won the War of the Currents in the late 19th century with the help of Nikola Tesla. The problem is, things have changed since then. Now, since a growing number of our systems and devices require DC power as opposed to AC, the War of the Currents has, in a way, been reignited. Implementing a DC power distribution system, or a DC microgrid, in a building are both good ways to supply electrical loads with the DC power they need, so they don’t have to waste energy with AC to DC conversions.
Brock Glasgo, a Cincinnati-based data scientist and engineer, put it best: “Eliminating unnecessary DC-AC and AC-DC conversions by distributing DC power would not only simplify our building-level power supply but would also save energy”.
So what are the options to distribute DC power in practice? First, let’s have a look at a DC power distribution system that’s been around for a couple decades: Power over Ethernet (PoE).
Power over Ethernet is a type of DC power distribution system that provides both power and data along a single cable. The most recent version of PoE is PoE Type 4, which came out in 2018, and typically provides about 90W (at a nominal 48V DC) of power per cable. Perhaps you’ve considered implementing PoE if you own a commercial or industrial building, as its control, safety, and efficiency features are enticing. But, PoE is expensive, and doesn’t offer nearly as much power as AC electricity. This makes it often impractical, and hard to justify. Unfortunately, there have been few other notable DC power distribution systems until, of course, the introduction of Article 726 in the 2023 edition of the NEC (Class 4 Power).
If you are familiar with the National Electrical Code (the NEC), you are probably aware that there are four different categories that a power system or circuit can fall into. They can either be categorized under “Wiring Methods” in the codebook, or be rated as Class 1, 2, or 3. But a new power system rating, Class 4, has been introduced in the 2023 edition of the NEC. This is the first time in over 45 years that a new class of power has been added to the code book (Class 3 was added in 1978).
Class 4 systems are exciting because they distribute DC electricity, as well as combine the efficiency and safety of PoE, with the power and distance capabilities of AC systems.
The Class 4 rating is applied to circuits that:
The Predefined Fault Conditions that a Class 4 Power System Would Monitor for Include:
Although each Class 4 power system would use its own technology to fulfill these requirements, certain Class 4 systems could achieve these results with integrated sensors, and intelligent software.
Since Class 4 systems are a pretty new concept, and they are similar to PoE in some major ways, it can be difficult to understand the difference between the two of them at first. Here’s a quick summary.
PoE is considered a Class 2 system in the NEC because of three major reasons:
Similarly, Class 4 systems are also considered safe from an electrical shock and fire initiation standpoint, but they are not power-limited. Instead, they are “fault-managed”. Another major difference between PoE and Class 4 systems is that PoE systems provide both power and data through a single cable, while Class 4 systems don’t necessarily do both. If Class 4 systems do involve data transfer, it could be executed via different methods, which we’ll discuss in the next section.
It’s also notable that PoE has been around for decades, and so there are many more companies that offer it, than those that offer Class 4 systems. It’s also notable that PoE has been around for decades, and so there are many more companies that offer it, than those that offer Class 4 systems. After Cisco developed PoE in 2000, more companies followed suit. Let’s break down the differences between PoE and Class 4 in more detail.
The typical maximum distance for the transmission of data and power with Power over Ethernet is 100 meters, or 328 feet. If the PoE powered device (PD, for short) is further than 100 meters, media PoE converters, switches or extenders can be used to extend the data over 100 meters, but power is still pretty much limited to 100m on standard gauges of Ethernet cables. But, the need for these increases the capital cost of installing PoE.
Class 4 systems are not a network data transmission system in the same way that PoE is. Class 4 systems typically transmit power over a cable, but have no specifications for data transmission. So Class 4 systems can send data via any means, such as over a wireless mesh network. Side note, the need for PoE systems to send both power and Ethernet data over one cable means PoE systems only work with CAT series cables. These are more expensive than typical certified 2 conductor cables (which are used in traditional low voltage systems), and so they are an extra consideration when weighing the cost of PoE.
As for applications, PoE can only be used with PoE enabled devices. Certain devices that have been developed for use with PoE systems include PoE enabled lighting, VoIP phones, Wi-Fi routers, security cameras, and even some computers. PoE is also limited by the amount of power it can supply to loads; It can only provide about 90W (or 48V DC) per cable, so it only really works in low power applications.
Conversely, power loads do not need to be specifically Class 4 enabled to work with a Class 4 electrical system. This is because Class 4 systems have power receivers that convert Class 4 power back to a required voltage (based on the application). Additionally, similarly to PoE, Class 4 systems typically only require low-voltage wiring practices, usually making mechanical protection for cables unnecessary (and bringing the cost of installation down). Despite being able to make use of low-voltage wiring practices, Class 4 systems can still safely provide up to 450 Volts DC. We’ll cover how Class 4 achieves this in our next section (about safety features).
Thus, a couple things make Class 4 power systems applicable to a wider range of applications:
It’s pretty unlikely to get shocked by a PoE system. If an electrical system is providing anything less than 60 Volts DC, it’s considered a Safety Extra Low Voltage (SELV) system. Also the power sourcing equipment (PSE) in PoE systems are intelligent, and must make a “handshake” with the powered device (PD) before any power can be delivered. So, if there’s any interruption between the PSE, and the PD, like a cut in the wire, power will not be delivered.
Class 4 systems are also considered safe, but their safety features come from the intelligence built into them (not from power limitations). In a Class 4 system, an onboard computer continuously monitors power cables between a Class 4 “transmitter” and “receiver” for defined safety parameters. It stops the flow of power if any of the defined faults (listed above) are detected. Then there’s an additional monitoring system that’s constantly checking to make sure the safety monitoring is still in operation. This differentiates Class 4 systems from the other class ratings defined by the NEC because, in Class 4 systems, safety is not ensured by power limiting devices, or external devices (such as fuses or breakers), but rather safety is managed based on the detection of faults by the Class 4 power source (also called a Class 4 transmitter).
Transmitters, you say? Receivers? Onboard computers? Sounds fancy. Does this mean Class 4 systems cost more than PoE?
Not necessarily. Although PoE has been hailed for being able to cut cabling costs in half because it transfers both power and data through one cable (instead of two), it can still be much more expensive for applications that require more than 100W. The power limitation of PoE systems means that bundles of cable are often necessary to deliver enough power to loads. As we discussed above, these cables aren’t cheap. For a PoE system, heavy gauges of CAT series cables must be used, which are more expensive than typical electrical cables, bringing the cabling cost for PoE systems up significantly. This can often negate the money saved from transferring both power and data through one cable. This is just one of the reasons we wouldn’t consider PoE systems cheap, especially for LED lighting applications. PoE systems can also be expensive because they often require additional equipment and network overhead, such as converters, switches, or extenders.
On the other hand, the market for Class 4 systems is only just emerging. So it’s hard to tell what the cost of these systems are. It really depends on individual companies, and how they price their Class 4 systems. Because Class 4 systems are typically higher power v.s. PoE, their cost in $/watt should theoretically be much lower.
One company that already offers Class 4 power systems is Cence Power.
We hope you’ve enjoyed this comparison of PoE and Class 4 power systems. Next, we’ll discuss one, big benefit that applies to both of these systems: their ability to distribute DC power.
We live in a world where investing in green technologies is not only good for the environment, but also the economy. And, with buildings making up such a large portion of our carbon footprint, it’s time to consider how we can make new and existing buildings more efficient with their power consumption.
Brad Koerner said it best at the Smart Building Conference (2020): “we need a revolution in just basic electricity before a lot of our smart building technologies will actually be implemented”.
So, although implementing smart building technology is a big step toward making buildings more green, building owners and managers would be remiss to continue to allow AC electricity to power devices that require DC electricity, such as many smart devices. LED lighting, all our digital devices, and an increasing number of HVAC systems, require DC electricity. In fact, according to the USGBC, DC consumption currently makes up about 74% of total energy loads in buildings that have EV charging stations, and HVAC equipment with DC motors. If these loads are getting AC power, 5 - 20% of electricity generated to power them could be wasted every time they’re turned on. In the past (unless we wanted to implement Power over Ethernet), this was a problem we had to live with. But now, with the influx of Class 4 power systems entering the market, it’s time to consider aligning electrical systems with the electrical needs of modern buildings, and implement DC power distribution.
Check out Cence Power's Class 4 Power System here: Cence HVDC
We improve the value of commercial and multifamily buildings with an intelligent DC power distribution system that's pain-free to install. It combines the benefits of low-voltage wiring practices with voltage capabilities of up to 450 Volts DC.
