Electricity You Can Safely Touch!? - Introducing Class 4 (CL4) Power Systems
August 15, 2022
Could Class 4 power systems replace Power over Ethernet (PoE), or more ambitiously, all alternating current (AC) electrical systems? Class 4 power (CL4) systems enable the distribution of direct current (DC) power at higher-voltages, and are safer than traditional AC electrical systems.
In this article we'll briefly cover what the electrical code is and the different levels to it. Then, we'll dive into how Class 4 systems fit into all this, and why they're so special. If you're already familiar with the electrical code, feel free to skip ahead.
You may be aware that there are currently four different categories that a power system or circuit can fall into in the National Electrical Code (NEC).
They could fall under the category of "Wiring Methods" in the Canadian Electrical Code (CEC)
Class 2 (ex. Power over Ethernet)
Class 3 (only in the NEC, not in the CEC)
But a new class rating (Class 4) has been introduced in Article 726 of the most recent edition of the National Electrical Code (NEC), which came out in early 2023. This new class rating is assigned to circuits that can send up to 450V DC, constantly monitor for faults, and shut power off almost instantaneously if any occur. In this way, Class 4 power systems have virtually zero risk for electrical shock or fire!
In this article we'll break down further differences between Class 4 circuits, the rest of the ratings for power systems, and what makes Class 4 so revolutionary.
A Brief Summary of Class Ratings in the Electrical Code
Most of the electrical loads in your building are inherently dangerous to wire because they have no intelligent way to actively prevent the risk of electrical shock or fire. This, in itself, is a little concerning seeing as electricity (especially AC power) can be dangerous, especially since us adults are unsupervised almost all the time, and very few of us understand how the electrical systems in our homes and buildings work.
Electrical systems in our buildings typically fall under a section in the Canadian Electrical Code (CEC) called “Wiring Methods'' (Section 12 of the CEC and OESC). The CEC states that the provisions in this section of the code book "apply to all wiring installations operating at 750 Volts or less, as well as to installations operating at voltages in excess of 750 Volts, except as modified by the requirements of Section 36". As you can imagine, this definition covers many circuits. Additionally, systems that fall under regulations relating to Wiring Methods also require a breaker panel or fuse box. Here's a screenshot from the codebook for your reference that defines what falls under wiring methods:
Circuits that do not fall under wiring methods, would typically be given a class rating, and any class rated power systems in a building do not require a breaker panel because they have built-in intelligence to prevent faults or safety risks to the user. The intelligence in Class 1, 2, and 3 rated power systems are rudimentary power limiting systems. These circuits are currently classified by the electrical codes in their respective countries, and a user or inspector can find out the class of a circuit by locating its power supply. In America, these circuits are classified as either Class 1, Class 2 or Class 3 by the National Electrical Code (NEC). The Canadian Electrical Code (CEC) (in Canada, of course) only classifies these circuits as either Class 1 or Class 2. Both the CEC and the NEC are reviewed and revised once every three years; the newest edition of the NEC came out in early 2023, and the next CEC will come out in 2024. What are these codes used for? Well, if you were an electrician in America, for example, and wanted to look up the proper installation, insulation, and grounding requirements and regulations for a circuit classified as either Class 1, 2 or 3, you would look in Article 725 of the NEC.
As mentioned previously, the 2023 edition of the NEC released a new Class rating: the Class 4 power system. The new class rating was added to acknowledge, and standardize, fault-managed power systems, which have been developing over the past few years. It's a big deal that the NEC released a new class rating because the last class rating to be added to the NEC was Class 3 in 1978, so this is the first time in over 45 years that a new class of power has been added to the code book. Being fault-managed, means that its intelligence is more developed than the other class ratings, which are just power-limited. Class 4 power system, of course, deliver Class 4 power, and a handful of suppliers have already developed names for their form of Class 4 power, including: Packet Energy Transfer (PET), Pulsed Power, and Digital Current™ (Cence Power's term for it).
But does the electrical code matter to the rest of us?
As we learn about how to supply electricity to our building systems and devices efficiently, it’s good to know what electrical loads are more risky to work with, and what power limitations exist on the circuits we’re using, or if there are any limitations at all. After all, we use electricity every day, so it’s good to know what types of circuits exist in our buildings and homes.
Additionally, technologies are becoming increasingly intelligent and plug-and-play, so learning about some basic electrical terminology will help you understand how electrical systems in your building work and how they’re evolving. For example, when we connect new light fixtures, they have always needed to be hard-wired in. But now, with the invention of Weight Supporting Ceiling Receptacles (WSCR), fixtures can be connected with a WSCR and an attachment fitting (like in the image below). This transforms installation methods that have been somewhat dangerous in the past, into easy plug-and-play experiences.
Knowing about technologies like this could help save time and money by making electrical projects easier, safer, and more future proof.
Circuits Identified by Class Vs. Traditional Wiring Methods
Essentially, circuits that require traditional wiring methods can provide more power to loads, but are more dangerous to work with than circuits with class ratings, this is because they don't have built-in power limitations. Additionally, they require a breaker panel or fuse box. On the other hand, circuits that would be classified as either Class 1, 2, or 3 in the NEC have built-in power limiters and don't require a fuse box or breaker panel. This makes them safer to work with, but also means that they don’t provide sufficient power to many electrical loads, making them mainly useful in low-voltage or low-power situations.
The Latest Innovation in Electrical Technology: Introducing Class 4 Power (CL4)
The technology involved in electrical systems hasn’t evolved much since Nikola Tesla won the war of the currents back in the late 1800s. So what if we told you there’s a new technology that can replace many circuits that use traditional wiring methods? ISE magazine provides a simple explanation of what defines a Class 4 power system: "Simply put, where traditional powering relied on lower voltage and power limits for safety, newer systems can rely on intelligent power sources to control the safety of otherwise hazardous voltages and currents." The intelligence involved in these systems is considered "digital" because an onboard computer monitors the power cables 1000s of times a second for defined safety parameters, stopping power flow if any type of fault is detected. Digital monitoring technologies are already being used to provide safety in things like:
It can provide voltages just as high as traditionally wired circuits (up to 450V DC)
Limits power flow by intelligently monitoring for faults
They can be as safe to work with as circuits classified as Class 1, 2, or 3, without the use of breaker panels or fuse boxes (because of their built-in fault management)
They can often make use of low-voltage wiring practices
Many Class 4 systems have made it safe to touch a live wire if their fault-management systems are up to par
This is an exciting advancement in electrical technology not only for electricians or electrical engineers, but for building designers, and technology enthusiasts as well. According to the NEC, Class 4 (CL4) systems are characterized by monitoring a circuit for faults and controlling the power transmitted to ensure the energy and power delivered into any fault is limited, but there’s much more to them than that.
The Biggest Benefit to Class 4 Power Systems: the Proliferation of DC Power Distribution
Class 4 power systems have many benefits in contrast to past circuits with built-in fault management, including that they use less copper or wiring, have higher voltage limits, and are inherently intelligent. Their disadvantage is mainly that their power sourcing equipment is significantly more complex. This disadvantage means that in many scenarios, it's overkill to use a Class 4 circuit. Despite this disadvantage, the advantages have led to the proposal of using Class 4 systems in place of traditional wiring in certain cases. This is a big deal since no other class rated circuits have been able to safely fulfill the voltage requirements of circuits that fall under the category of "wiring methods" in the NEC. If Class 4 power systems can replace traditional wiring (which traditionally distributes AC power), a huge benefit to this will be that it will enable the proliferation of DC power distribution throughout the building industry. In turn, this will bring more buildings closer to operating at net-zero.
In support of this, Smart Buildings Technology mentions that, according to Luis Suau (chief business officer with Sinclair Digital, LLC),
"it’s now more about the improved efficiency, sustainability, and safety achieved by replacing AC power with DC power throughout the building".
Additionally, Sinclair points out that after switching to DC power distribution throughout their building (thanks to Power over Ethernet and other DC power distribution systems),Sinclair Hotel uses 39% less power.
What are the Differences Between Each Existing Class?
Before we dive deeper into Class 4 power systems, it’s essential that we break down the primary differences between Class 1, 2, and 3 circuits in the NEC. We’ll also cover any differences between circuit classifications in the NEC and the CEC. Understanding these class ratings better will help to clarify how Class 4 circuits differ from them. These differences are often dependent on various situations, so this guide is no replacement for the code books in your own country, but we hope these tables will help you understand general differences between classes, when certain class ratings would be applied, and what the purpose of this whole electrical rating system is.
Table 1.1: National Electrical Code NEC
This table differentiates between circuits rated by the NEC as either Class 1, 2, or 3. Many of these same rules apply to the CEC as well, and if you want to see some of the specific primary differences between the NEC and the CEC, you can jump to Table 2.
Things you should know before reading this table:
Power Limited: Limiting the output-side of the circuit to 30 volts and 1000 Volt-Amps (VAs)
Remote-Control and Signal Circuits: Limited to 600 Volts
Class 1: Power Limited
Class 1: Remote-Control and Signal Circuits
Class 1: In General
Equipped with overcurrent protection that will limit the amount of current on the circuit in the event of an overload, short or ground fault condition.
The current limiter present on a power source of a power limited circuit, is an Overcurrent Protection Device (OCPD).
Class 1 power-limited circuits are allowed to have higher power ratings than Class 2 or 3 circuits. Not restricted to specific uses.
If the interruption or failure of equipment on conductors involved in a remote control circuitry, or Class 2 or 3 circuitry, imposes a direct fire or life hazard, then these circuits are classified as Class 1 only.
Restricted to remote control operations.
Very common in commercial and industrial settings.
Must meet a lot of the same wiring requirements as power and light circuits.
2 levels of protection (insulation of conductors and a means of connection to the Earth protective conductor (Earth wire)).
If the rating plate does not have a double box then assume Class 1.
Class 1 circuits can occupy the same cable, enclosure, or raceway without regard to whether the individual Class 1 circuits are AC or DC, provided all the Class 1 conductors are insulated for the maximum voltage of any conductor in the cable, enclosure, or raceway.
Class 1 circuits can be 600 Volts or less, but are usually 120 Volts due to the preferences of OSHA inspectors.
The NEC defines a Class 2 circuit as the portion of a wiring system between the load side of a Class 2 power source and the connected equipment.
Class 2 circuits should only be connected to a power supply with a load side that has a rating of less than 100VA and a voltage of up to 30 volts.
Class 2 circuits have at least 2 layers of insulation: basic insulation and a plastic case on device.
Class 2 systems can reduce insulation requirements, wire size, installtion materials and more; implementing it can therefore reduce the cost of wiring and improve the flexibility of a system.
Requires dry, indoor use.
Only for non-hazardous locations.
Circuits must be grounded.
Two or more Class 2 circuits are permitted within the same cable, enclosure, or raceway.
Considered safe from a fire initiation standpoint and provides acceptable protection from electric shock.
The output of equipment supplying Class 3 circuits is known as Separated Extra-Low Voltage (SELV) because its voltage mustn't exceed 50 V AC (normally between 24-12 V).
If the voltage demand is higher than 30 V, but equals less than 100 VA, a Class 3 circuit is used.
Considered safe only from a fire initiation standpoint, not from electric shock. This means Class 3 cables are required to have a higher voltage rating (at least 300 Volts).
The output voltage can reach values up to 100V DC on a 100VA power level.
The separation between the windings in transformers present in Class 3 equipment is the equivalent of double insulation; safety in Class 3 circuits comes from the isolation in transformers.
Table 1.2: National Electrical Code NEC Applications
Class 1: In General
Any portable applicances without a Class rating should be treated as a Class 1 appliance
When the failure of a circuit component can create a significant hazard, such as an explosion or fire, a Class 1 circuit must be used (instead of a Class 2 or 3 circuit)
Motor controllers (which operate mechanical processes)
Power over Ethernet (PoE)
Home theatre and sound systems
Table 2: Primary Differences Between the NEC and CEC
The CEC has established two categories for Class 1 circuits:
Extra-Low-Voltage Power Circuits:
Rated output of not more than 30 V and 1000 VA, conforms to the limitations of a Class 2 circuit.
Remote-Control and Signal Circuits:
Limited to 600 Volts, controlled via a relay
Class 2 Circuits:
Maximum voltage and power rating of a Class 2 circuit: 150 V and 100 VA.
The maximum voltage of a Class 2 circuit that can be supplied by a primary battery is 30 V.
There is a current limit that depends on the voltage in Class 2 circuits.
For Class 2 circuits with a voltage of 0 - 20 Volts overcurrent protection should not exceed 5 A.
For Class 2 circuits with a voltage over 20 V but not exceeding 30 V overcurrent protection rating in amperes not exceeding 100 VA divided by the open circuit voltage. In this case, primary batteries that under short-circuit will not supply a current exceeding 5 A after 1 min.
For Class 2 circuits with a voltage over 20 V but not exceeding 60 V overcurrent protection rating not exceeding 100 VA divided by the open circuit voltage.
Class 1 in General
If the rating plate does not have a double box then assume Class 1.
There are specific rules for when a Class 1 circuit would have overcurrent protection, and how much overcurrent protection it would have.
Same as NEC.
Same as NEC.
Where do Class 4 Circuits Come In?
So far we've defined the primary differences between the established class ratings, and reviewed what the major differences are between rating systems in Canada and America. The purpose of this next section will be to go over the main differences between these established class ratings, and the proposed Class 4 rating. Note that, for the purpose of this section, we’ll compare Class 4 power systems to the class rating system present in the NEC, and won't be covering specific differences between the NEC and the Canadian Electrical Code (CEC).
Class 4 circuits differ from the other Class rated circuits in 4 ways:
They can handle higher voltages than Classes 1 - 3
They're built differently
They limit power based on fault conditions rather than by a defined voltage limit
Required safety precautions
1. They can handle higher voltages than Class 1 - 3
Keep in mind that this table assumes that the power source is inherently limited (so overcurrent protection such as breaker panels and fuse boxes are not required).
Class 1: Power Limited
Depends on voltage
Depends on voltage
Class 1: Remote-Control and Signalling Circuits
Depends on voltage
150 V maximum
Depends on voltage
60 V - 100 V
150 Amps maximum
450 V line to line and 225 V line to ground
See "Takeaways" for more detail on this
Takeaways From The Above Table
Additional comments on voltages and implications of data in the table.
Class 4 power systems mainly use DC power. DC power is only made up of active power, which is why watts are used to measure power instead of Volt-Amps (apparent power). Class 2 power systems also mainly use DC power.
Should be able to limit 100W of current in Class 4 power systems in the span of 5 seconds after any fault condition.
Current is limited by the cable (the gauge or the thickness of copper that’s used in the wire). Because Class 4 systems (mainly) use entirely DC electricity, and DC electricity is entirely active power, less wire and copper is necessary in Class 4 systems in comparison to AC systems of the same current or voltage. You can read more about this in our article about the benefits of DC power in buildings.
Class 4 power systems are very similar to Class 2 power systems (the class assigned to PoE power systems), the main difference between them is that Class 4 systems can carry high voltages. So why would you use a Class 2 system when you could use a Class 4 system? Class 2 systems still have their purpose in low-voltage applications because they are typically much more simple to implement than Class 4 systems. Essentially, using Class 4 for a low-voltage, Class 2 application, would be overkill. It would be worth it to replace a Class 2 system with a Class 4 system in applications where there's an advantage to reducing copper, wiring, or increasing the voltage. Think of it this way: Class 4 is an advanced version of Class 2 power with added safety features.
See the table below for more information from the NEC about Class 2 and Class 3 DC powered circuits:
In point-to-point configurations, Class 4 power systems often consist of a Class 4 power transmitter and a Class 4 power receiver connected by a cabling system. On the other hand, the established class rated circuits (circuits rated Class 1 - 3) are defined by the NEC as circuits that constitute the portion of the wiring system between the load side of the overcurrent protection device (OCPD) or the power-limited supply and all connected equipment.
Here are a couple definitions that will help you understand how a Class 4 circuit is built to connect a power transmitter and receiver in a point-to-point configuration:
Power Transmitter: In the Cence Class 4 power system (Cence HVDC), for example, a power transmitter receives power from an AC power supply, converts it to DC power, and has intelligence built in to monitor for things such as fault conditions (often with a microcontroller).
Power Receiver: In general terms, the definition for a receiver involved in electrical devices is a device that, "accepts signals, such as radio waves, and converts them (frequently with amplification) into useful forms. Examples are telephone receivers, which transform electrical impulses into audio signals, and radio or television receivers, which accept electromagnetic waves and convert them into sound or television pictures".
In the Cence Class 4 power system, specifically, a receiver is a device that connects to the Class 4 transmitter to provide confirmation that a safe physical connection has been established. Then the receiver communicates with the transmitter to let it know that it's now safe to send power. The receiver can also have the ability to convert from Class 4 to Class 2 power at its output (which essentially means that it can lower voltage levels). In this way the receiver in Class 4 power systems acts as an interface between a Class 4 power system and a Class 2 power system.
3. They limit power based on fault conditions rather than by a defined voltage limit
Circuits given a class rating of Class 1, 2, or 3 have mainly one thing in common: they all have power limiters. Class 1 power limited circuits, for example, use a built-in overcurrent protection device (OCPD) to limit current flow. According to Safeopedia, the most common OCPDs are fuses, circuit breakers, and overcurrent relays. Class 4 circuits, on the other hand, are characterized by incorporated, intelligent technology that does two things:
Monitors the circuit for faults
Controls the power transmitted to ensure the energy and power delivered into any fault is limited
Essentially Class 4 power systems monitor energized circuits for faults, and control the power transmitted to ensure that, if there’s a fault, a very limited amount of power or energy is delivered to it.
Additionally, Class 4 systems differ from Class 1, Class 2, and Class 3 systems because Class 1, 2, and 3 systems have a defined power limit based on their cable or connected load. On the other hand, Class 4 systems are limited with respect to risk of shock and fire between the Class 4 transmitter and Class 4 receiver. This allows them to deliver much higher levels of power and voltage to loads, even without a breaker, fuse box, ground wire, or significant insulation. There is, however, still a power limitation on Class 4 circuits; they are supplied by a power source (transmitter) that has a peak voltage output of not more than 450V DC line to line, or 225 Volts DC line to ground.
Aside from this power limitation, the transmitter used in Class 4 power systems only limits current flow based on predetermined fault conditions. The transmitter gathers and decodes information about a circuit in real-time, and interrupts its power flow when any of these fault conditions occur:
An abnormal condition such as abnormal voltage, current, waveform, or load condition is identified in the system
A short circuit
Human skin contact on energized parts
A ground-fault condition
An overcurrent condition
Intentional shorting of the line at the receiving or transmitting end to force de-energization for purposes of maintenance or repair
Because Class 4 systems interrupt power flow so quickly when a fault occurs, they have the equivalent level of protection from electric shock as Class 2 circuits.
4. Required Safety Precautions
The safety precautions that exist in circuits rated Class 1 - 3 have two things in common: they all have built-in overcurrent protection devices (OCPDs), and their safety requirements are very layered and complex. If you want to know about the power limitations that OCPD devices apply in each case, you can see them in the table above. Aside from this, the safety requirements applied to each class rating differs with respect to other factors. These factors may include, but are not limited to:
Different rules regarding whether or not circuits can share cables and under what conditions this can occur
Minimum conductor sizes
For example, Class 1 circuits require 2 levels of protection: insulation of the conductor (such as a copper wire) and a means of connection to the Earth's protective conductor (Earth wire). On the other hand, Class 2 circuits require at least 2 layers of insulation: basic insulation and a plastic case on devices. Additionally, Class 2 circuits are considered safe from a fire initiation standpoint and provide acceptable protection from electric shock, whereas Class 3 circuits are only considered safe from a fire initiation standpoint, not from electrical shock.
The safety requirements for Class 4 systems are quite different (based on what we know so far from the proposal). For one thing, Class 4 power systems do not involve a built-in overcurrent protection device (OCPD). Instead, they monitor for faults in real-time, and shut off power when a fault occurs.
This is the full list of safety requirements for a Class 4 circuit:
Non-interchangeability: Receptacles, cord connectors, and attachment plugs used on Class 4 distribution systems shall be constructed so that they are not interchangeable with other receptacles, cord connectors, and attachment plugs.
Guarding: Any junctions and mating connectors shall be constructed and installed to guard against inadvertent contact with live parts by persons.
Voltage Limitations: Output of not more than 450V DC line to line, or 225 Volts DC line to ground.
Power Shutoff in the Case of a Fault: The transmitter shall interrupt an energized circuit within the limits of section 726.121(A) in the NEC when any of the fault conditions occur (which are defined by the transmitter). Power is shut off within 5 seconds of a fault occurring.
An abnormal condition such as abnormal voltage, current, waveform, or load condition is identified in the system
Short circuit occurs
Human skin contact with energized parts
Ground-fault condition exists
Overcurrent condition exists
Malfunction of the monitoring or control system
Intentional shorting of the line at the receiving or transmitting end to force deenergization for purposes of maintenance or repair occurs
As you can see, there are many benefits to Class 4 power systems. However, these are the main takeaways:
Class 4 systems can safely deliver higher voltages than other class rated circuits
They can deliver these higher voltages safely thanks to their built-in intelligence (digital monitoring and fault management)
Class 4 power system could proliferate the use of DC power throughout buildings
The most recent edition of the NEC (released in February 2023), contained the addition of Article 726. Article 726 defines a Class 4 rating, which can be applied to power systems with fault management, and other credentials. Thus, Class 4 power systems are also known as fault-managed power systems. Power over Ethernet (rated as Class 2) used to be the new and exciting technology, but it has its limitations, and Class 4 power systems can provide the same benefits as PoE, but with the capacity to provide higher voltages (up to 450V DC) than PoE systems (up to 60V DC, or 100W). We know that, even though PoE has its limitations, the market for it continues to grow due to its many advantages. In fact, PoE is anticipated to grow from $113.8 million in 2021 to $614.9 million by the end of 2030. If this is the case, imagine how popular Class 4 power systems will be once they proliferate the market (seeing as they can distribute higher voltage levels than PoE with the same benefits).
Eventually, Class 4 power systems can even replace the need for some circuits that fall under Wiring Methods in the Canadian Electrical Code (CEC), which will make working with electrical systems in our buildings safer, and sometimes maybe even replace the need to hire an electrician. In buildings where Class 4 circuits replace traditional Wiring Methods, breaker panels and fuse boxes won't be necessary, so it would be interesting to see the implications of this in action.
Erin is the Creative Director at Cence Power. She has a New Media degree from the University of Toronto and 5 years of experience in the communications field. She has also done digital content creation for dozens of clients through her own business called Story Unlocked. Erin loves technology, especially when it makes the world a better place.
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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.