PoE for Industrial Automation: Power, Data and Control over a Single Cable Solution Brief

Executive overview

It has been 20 years since the first Power over Ethernet (PoE) standard was ratified by IEEE. Called IEEE 802.3af, this first standard provides up to 15.4W of DC power per port. With this standardization, PoE quickly gained popularity, as it allowed a reduction in infrastructure costs, simpler installation, improved flexibility, and increased reliability. It also allowed organizations to better optimize power consumption by being able to use the network to control power to connected devices. The first implementations had narrow applicability, and IEEE has introduced newer standards over the years, with the latest, IEEE 802.3bt Type 4, also called 4-pair PoE (4PPoE) or PoE++, able to supply up to 90W per port.

After its initial deployment in enterprises, PoE is now becoming popular in the industrial sector, where devices frequently require higher wattage and better control, and where sustainability issues are front and center.

To take full advantage of PoE, and to facilitate its rollout on a large scale, organizations must properly plan its deployment, considering the right power sources, proper cabling, and network design. They also need to be able to monitor, manage, and troubleshoot promptly to help ensure uninterrupted operations.

This paper explains the basics of PoE, explores how the industrial sector can benefit from PoE technology, and describes the PoE capabilities that Cisco^® industrial switches offer and the tools available for proper design, monitoring, and deployment.

What is PoE?

PoE works by injecting low-voltage Direct Current (DC) power onto an Ethernet cable, alongside the data signals. This power is then extracted at the receiving end by compatible PoE-enabled devices, which can use power supplied through the Ethernet cable to operate without requiring a separate power source.

In PoE nomenclature, Power Sourcing Equipment (PSE) is used to refer to the entity that injects power into the Ethernet cable, and Powered Device (PD) refers to the device that consumes power. Typically, the PSE is an Ethernet switch, but it can also be special power injectors that are distinct from the switch. In this document, we will assume that the PSE is an Ethernet switch.

An Ethernet cable contains multiple copper conductors. These conductors are twisted together to reduce interference from external sources. The most common type of Ethernet cable, known as twisted pair cable, consists of four pairs of twisted copper wires. The early PoE standard, IEEE 802.3af, uses two of the four pairs to deliver power, while the data transmission occurs over the remaining two pairs. Later standards use all four twisted pairs in an Ethernet cable for power transmission and can provide significantly higher power levels compared to previous PoE standards.

Benefits of PoE

The benefits of PoE include simplified installation and deployment, as it eliminates the need for additional power outlets near devices. It also allows for easier scalability and flexibility in network infrastructure design, as devices can easily be added or relocated without the need to worry about power outlets. Additionally, PoE provides centralized power management and can enhance reliability and continuity of power delivery by providing backup power options for the source.

Sustainability

PoE can reduce costs and increase sustainability in several ways.

●      PoE eliminates the need to run extra copper cabling and steel conduits to each device.

●      PoE delivered through network equipment allows for easy monitoring and control of power consumption. Power can be shut off or reduced to nonessential devices when they are not in use.

●      AC-DC conversion losses, that could add up to 20%, can be avoided by using PoE to power devices that natively run on DC.

●      PoE delivered through ruggedized networking equipment helps reduce overall cooling costs.

Safety

PoE can also help make industrial operations safer. These include:

●      PoE operates at lower voltage, typically 48V, which is considered safe for handling by individuals, whereas traditional power cables can carry higher voltages, increasing the risk of electric shock or electrical hazards if not handled properly.

●      PoE reduces the risk of short circuits, exposed wires, or accidental contact with high-voltage wires that can occur when running separate power cables.

●      PoE devices are designed to provide overload protection, which defends against excessive power consumption and potential damage to devices or cables.

●      PoE switches and devices have built-in safeguards that monitor power usage and can shut down or limit power delivery if an overload is detected, protecting the connected equipment, and reducing the risk of overheating or fire.

●      PoE technology adheres to safety standards and procedures, ensuring that PoE-enabled devices, cables, and PSE meet specific safety regulations. Compliance with these standards helps ensure that PoE installations are safe and reliable.

PoE standards

IEEE has defined several PoE standards since the first standard, IEEE 802.3af, was ratified in June 2003. Table 1 shows the current IEEE standards and the maximum power they are rated for. Note that for 30W or higher, a 4-pair Ethernet cable is required, since all pairs are necessary to deliver the power.

Table 1.        IEEE standards defining PoE

Before the IEEE standards came into force, Cisco developed its own PoE standards. However, we shall not be discussing those in this document, as Cisco’s current portfolio of switches support the IEEE standards.

Figure 1 illustrates the PoE standards and the typical devices that can be powered through each.

Typical PoE-powered devices

Power availability at powered devices

While the standards specify the nominal power delivered from the PSE, the actual power available at the PD may be less because of losses in transmission. Typically, in enterprise environments these losses are between 10% and 15%, For example, the net available power might be only 51W at the device when connected to a source capable of delivering 60W. These losses may be magnified in industrial environments, as discussed below. The power availability consideration must be part of the industrial network design.

Table 2.        Maximum power available for powered devices

PoE in industrial environments

The advantages of PoE in enterprises are even more relevant to industrial use cases. In industrial environments, PoE brings more reliability and helps reduce downtime. It can also reduce the need to run high-voltage power cables, which increases operations safety.

However, it can be more challenging to provide PoE in harsh environments. Some of the unique requirements of industrial deployments are listed in Table 3.

Table 3.        Industrial PoE deployment considerations

Cisco Industrial Ethernet portfolio

For over 20 years, Cisco has offered a comprehensive portfolio of industrial switches, routers, and wireless devices. Purpose-built for industrial use, these devices provide seamless communications for every industrial sector. Cisco industrial switches are resilient to minimize downtime, support communications protocols between control systems and machinery with minimum delay, and protect operations with visibility, data encryption, and network segmentation. The reader is directed to the data sheet for each switch for the exact specifications for the switch (see Table 4).

PoE support

Several of the Cisco Industrial Ethernet switches are designed to provide PoE to connected devices. There is variation in the supported standard, the number of ports available for PoE, and the total available power budget. Table 4 summarizes the switch characteristics.

Table 4.        Cisco Industrial Ethernet switch models and PoE support

Power supplies

DIN-rail PSUs provide DIN-rail switches power for switching functions as well as for PoE. You must use the power supply rated for the PoE power you need from the switch. Table 5 lists the available DIN-rail PSUs, IP67-rated PSUs, and rack-mount PSUs and their support for PoE.

Table 5.        Industrial power supply units and PoE support

Choosing the right power supply for your powered devices

Your selection of the power supply unit determines the PoE power budget for powered devices. Make sure you budget for your current and planned PDs. Calculate the total power you will need by adding the maximum power requirement for each PD with the power required for the functioning of the PSE itself.

For example, let’s assume our PSE is Cisco IE- 3300-8T2X with the IEM-3300-8P expansion module. In this case, the power required by the switch and expansion module, as documented in the Catalyst IE3300 Rugged Series data sheet, is 28+14=42W. Now assume, that we want to connect 4 PDs that draw 30W each and 2 PDs that draw 7W each. Then the total power budget required will be 4*30+2*7=134W. Therefore, the minimum draw from the power supply will be 42+134=176W. In this example, we will need at least the PWR-IE240W-PCAC-L model PSU. You may also use the Cisco Power Calculator, a tool that helps you calculate power supply requirements for a specific Power over Ethernet (PoE) configuration.

Note that you may also need to account for performance characteristics of power supplies in extreme environments. Please refer to power supply datasheets for more information.

Deployment considerations for large-scale PoE

Large-scale PoE deployment can present several challenges. Some of these include:

●      Power budget limitations: In large-scale deployments, where numerous devices are connected to the same network switch, the available power budget may become a constraint. This can impact the number and types of devices that can be connected and may require careful planning and management.

●      Distance limitations: In large-scale deployments, where devices are spread across a wide area, ensuring that each device receives sufficient power may require additional network infrastructure, such as intermediate switches or power injectors.

●      Power management and monitoring: Managing and monitoring power consumption in large-scale PoE deployments can be challenging. It is important to ensure that each device is receiving adequate power and to be able to identify any power-related issues or failures quickly to avoid unplanned downtimes.

●      Heat dissipation and cooling: In large-scale deployments, where numerous devices are concentrated in a confined space, managing heat dissipation, and ensuring proper cooling become crucial to prevent overheating and device failures.

●      Network design and scalability: Designing a network that can support many PoE devices requires careful consideration of the network architecture, capacity, and scalability. It may involve deploying multiple switches, dividing the network into logical segments, and ensuring proper network performance and reliability.

●      Power backup and redundancy: In critical applications, it is important to have backup power solutions to ensure continuous operation in the event of a power outage. Implementing power backup systems, such as uninterruptible power supplies, and designing redundant power paths become important considerations in large-scale PoE deployments.

●      Compatibility between PSE and PD: Before power transmission can start, PSE and PD must communicate to determine the PD's power requirements. This negotiation determines if the two are compatible and if the PD can safely receive the power it requires. A successful negotiation prevents the PD from receiving too much or too little power, which could damage the device or cause it to malfunction.

●      Power hazard prevention measures: Best practices to prevent electrical accidents must be followed. These practices include: regularly inspecting electrical cords, avoiding electric circuit overloads, using surge protectors with built-in circuit breakers, proper grounding to reduce the risk of electrical faults. These practices can help prevent damage to both PSE and PD.

Although, Cisco industrial switches clearly fulfill a lot of these requirements, you also need a central reporting and monitoring mechanism, without which you would need to poll each PoE-enabled switch, which can be time consuming and error prone.

Cisco Catalyst Center (formerly Cisco DNA Center) is a network management solution that provides real-time analytics for networks. In addition to other features, it provides a PoE Analytics dashboard. This dashboard provides information on all PoE equipment in the network, including each switch's power budget, power usage, and remaining available power. Figure 2 shows the dashboard and the insights it can provide on PoE deployments.

Cisco Catalyst Center PoE Analytics dashboard

PoE analytics in Cisco Catalyst Center can be enabled by setting up workflow for PoE telemetry, which consists of configuring NETCONF on Catalyst IE switches as well as telemetry settings for PoE telemetry in Cisco Catalyst Center. Details on the minimum versions required and how to set this up can be found in the Cisco DNA Assurance User Guide, which can be found at the Cisco Catalyst Center End-User Guides page.

The PoE Analytics dashboard in Cisco Catalyst Center provides analytical information that can help you plan and monitor your PoE deployment and usage, as explained in Table 6.

Table 6.        Cisco Catalyst Center PoE Analytics dashboard

More details and troubleshooting information can be found in Cisco Catalyst Center’s Assurance screens using Device 360. For more information on this, please refer to the Cisco Catalyst Center documentation.

Closing

Overall, PoE is useful in industrial environments due to its simplicity, flexibility, cost savings, remote management capabilities, reliability, and safety features. But deploying it at scale requires proper planning, selection of appropriate equipment, and adherence to industry standards.

Check out the Cisco industrial switching portfolio, which offers a variety of PoE options suitable for deployment outdoors and in harsh environments. To quickly identify the right Cisco switch for your needs, use our switch selector.

For specific questions, please schedule a free, no obligation, consult with a Cisco industrial switching expert.