Phoenix Contact FL SWITCH 1108 Wiring (24V DC, DIN-Rail)

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1. Understanding the Industrial Necessity of the FL SWITCH 1108

The integrity of a control system hinges on robust communication infrastructure. In industrial environments, where conditions are harsh and downtime is costly, the choice of networking hardware is critical. The PHOENIX CONTACT FL SWITCH 1108 is widely deployed for its straightforward, plug-and-play nature coupled with industrial-grade resilience. As an unmanaged Gigabit switch with 8 ports, it provides essential high-speed data transfer capacity without requiring complex configuration, making it a staple for connecting PLCs, HMIs, I/O modules, and industrial PCs within a control cabinet or production line segment.

This guide focuses solely on the physical installation and electrical wiring—the core tasks an automation technician performs on-site—to ensure the switch operates reliably in its demanding environment. Incorrect installation, particularly wiring for power and grounding, is the leading cause of field failures, making this technical knowledge indispensable.

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2. Physical Installation: Secure Mounting on the DIN Rail

Proper mounting is the foundational step for maximizing the thermal performance and mechanical stability of the switch. The FL SWITCH 1108 is designed for DIN rail mounting (TH 35).

2.1. Choosing the Optimal Mounting Location

The switch should be positioned to minimize cable length and maximize airflow.

• Thermal Management Consideration: Since the FL SWITCH 1108 is passively cooled, it relies on convection. In a control cabinet, technicians must ensure that no heat-generating components (like large power supplies, transformers, or high-power drives) are mounted directly below the switch. A minimum clearance of 20-30 mm above and below the unit is a common best practice to facilitate vertical airflow, even if the manual suggests less.
• Vibration and Shock Isolation: For environments with high vibration (e.g., near heavy machinery or stamping presses), the mounting rail must be firmly secured to the cabinet backplate. A technician should verify that the DIN rail clip mechanism is fully engaged and locked to prevent the switch from rattling, which can stress the power terminals and Ethernet ports over time.

2.2. The DIN Rail Attachment and Detachment Procedure

The mounting process is typically tool-free and involves two primary steps:

• Attachment: Hook the upper lip of the switch’s mounting bracket over the top edge of the DIN rail. Pivot the bottom of the switch toward the rail until the internal spring-loaded or locking mechanism clicks into place. A clear, audible click is the engineer's sign that the mechanical installation is secure.
• Detachment: Locate the release lever or tab, usually at the bottom or top of the housing. Using a standard flat-head screwdriver, a technician should firmly pull or depress the lever to disengage the lock, allowing the bottom of the switch to swing out. Applying too much force without releasing the lock can damage the plastic housing or the rail itself.

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3. Critical Power Supply Wiring (DC 24 V)

The stability of the industrial network is intrinsically tied to the quality of the 24 V DC power supply wiring. The FL SWITCH 1108 uses a plug-in terminal block for power connection.

3.1. Power Terminal Configuration and Wire Sizing

The power terminal block typically features two pairs of connection points: $V_{1}^{+}$ and $V_{1}^{-}$, and $V_{2}^{+}$ and $V_{2}^{-}$. The dual terminals allow for redundant power wiring, or more commonly in simpler installations, provide convenient points for loop-through power to another adjacent device on the DIN rail.

Parameter	Standard Specification	Technician's Best Practice Guidance
Input Voltage	12 V DC to 48 V DC (Nominal 24 V DC)	Strictly adhere to 24 V DC ($\pm 10\%$) from a dedicated, industrial-grade power supply (e.g., TRIO POWER series) to prevent voltage instability.
Wire Cross Section	0.2 mm$^2$ to 2.5 mm$^2$ (AWG 24 to 14)	Use a minimum of 1.5 mm$^2$ (AWG 16) stranded wire. While the switch current draw is low, the larger cross-section minimizes voltage drop and provides mechanical ruggedness at the terminal block.
Stripping Length	Approximately 8 mm	Use a ferrule (wire end sleeve) for all stranded wires to prevent fraying and ensure a gas-tight, vibration-resistant connection. The ferrule should fit fully inside the terminal opening.

3.2. Implementing Redundant Power (Optional but Recommended)

In critical applications, connecting the switch to two independent 24 V DC power sources is recommended, even for an unmanaged switch. This is achieved by connecting Source A to $V_{1}^{+} / V_{1}^{-}$ and Source B to $V_{2}^{+} / V_{2}^{-}$.

• Decision Flow: If the application has a high cost of downtime (e.g., continuous process manufacturing), a dual-redundant power source should be used. If the switch is only connecting non-critical HMI panels, a single, reliable power source with adequate surge protection is acceptable.

3.3. Polarity Verification and Connection

Before applying power, the technician must use a digital multimeter (DMM) to verify the polarity of the cable leads from the power supply. Reversing polarity will not necessarily damage the switch immediately due to internal protection circuits, but it can lead to intermittent failure and is a serious wiring error. Positive ($+$) leads must connect to $V^{+}$ terminals, and Negative/Ground ($-$) leads to $V^{-}$ terminals.

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4. Essential Grounding and Shielding Techniques

Proper grounding (earthing) is arguably the most critical step in industrial installation, especially for network devices, as it manages electrical noise (Electromagnetic Compatibility - EMC) and ensures safety.

4.1. Functional Grounding via the DIN Rail

The FL SWITCH 1108 typically uses the DIN rail itself as the primary path for functional grounding (PE - Protective Earth).

• Grounding Checklist: A technician must verify the following:
  • The DIN rail is conductive and not painted or coated where it contacts the backplate.
  • The DIN rail is connected to the cabinet's main grounding busbar via a low-impedance conductor (braided cable or thick wire).
  • The grounding connection is tightened to the manufacturer's specified torque. Loose ground connections are a major source of noise coupling into the network.

4.2. Managing Ethernet Cable Shielding (Screening)

The industrial environment is rich in electromagnetic noise from variable frequency drives (VFDs), contactors, and motors. This noise is coupled through the Ethernet cable shield.

• Technician's Practical Guide to Shielding:
  • Always use Shielded Twisted Pair (S/FTP or F/UTP) cable in the control cabinet. Unshielded (UTP) is insufficient in close proximity to power electronics.
  • Connect the cable shield at both ends (switch port and connected device port) using industrial-grade RJ45 connectors with metal housings that ensure 360-degree connection to the cable braid.
  • Cable Routing Rule: If a control cabinet panel has both high-voltage power cables (e.g., 400 V AC) and low-voltage network cables (e.g., Ethernet), the cables must not run parallel to one another. If they must cross, they should do so at a 90-degree angle to minimize inductive coupling. This decision-making process is critical to avoiding intermittent communication errors that are difficult to diagnose later.

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5. Network Connectivity: RJ45 Port Wiring and Cable Selection

The FL SWITCH 1108's ports are the interface to the rest of the automation system. Correct cable choice and termination are paramount for achieving the promised Gigabit performance.

5.1. Cable Category Selection and Field Termination

The switch operates at Gigabit speed (1000 Mbps).

• Cable Choice Flowchart:
  • Required Speed is Gigabit: Use a minimum of Category 5e (Cat 5e) cable, although Category 6 (Cat 6) is preferred for better headroom against crosstalk and noise.
  • Required Distance is less than 90 meters (295 feet): Cat 6 is preferred.
  • Required Distance is near the 100-meter limit OR the environment is extremely noisy: Use a Cat 6A (Augmented) cable to ensure signal integrity.
• Termination Standard: All Ethernet cable connections to the switch must follow the T568B standard (Orange/White, Orange, Green/White, Blue, Blue/White, Green, Brown/White, Brown) for color coding, as this is the prevalent standard in industrial automation in most regions. Incorrect pairing (T568A or mixed) will not allow the Gigabit signal to properly negotiate.

5.2. Understanding Auto-Negotiation and Auto-Crossover (Autosensing)

As an unmanaged switch, the FL SWITCH 1108 simplifies connection by supporting:

• Auto-Negotiation: The switch automatically determines the optimal connection speed and duplex mode (10/100/1000 Mbps, Half/Full Duplex) with the connected device.
• Auto-Crossover (Auto-MDI/MDIX): The switch automatically detects the pin configuration of the connected device. This is a massive time-saver for field technicians, meaning there is no need to worry about using specific straight-through or crossover cables; any standard straight-through Cat 5e/6 cable will work for connecting PC-to-Switch or PLC-to-Switch.

5.3. Port Status Indicators (LEDs) for Troubleshooting

The status LEDs are the primary diagnostic tool for an unmanaged switch. A technician relies on the LED behavior to confirm a successful installation:

LED Status	Indication	Technician's Diagnostic Action
Link/Activity (Green - Steady)	Successful physical layer connection.	Confirms cable integrity and proper termination. Installation complete for that port.
Link/Activity (Green - Flashing)	Data activity (traffic flow).	Confirms the connected device is communicating.
Link/Activity (Off)	No physical connection or power issue.	Check the cable at both ends. Verify the connected device is powered on.
Speed (Amber/Yellow)	Connection is at 10/100 Mbps (Fast Ethernet).	If Gigabit (1000 Mbps) is expected, check the cable quality or the connected device’s setting (e.g., an older HMI may only support 100 Mbps).

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6. Installation Environment Check: Beyond the Control Cabinet

While the primary installation occurs in a protected control cabinet, the FL SWITCH 1108’s performance can be impacted by its external environment, particularly for copper cables running to external field devices.

6.1. Environmental Specifications and Conditioning

Industrial switches are designed for extended temperature ranges. The FL SWITCH 1108 series typically operates reliably between $-10^\circ \text{C}$ to $+60^\circ \text{C}$.

• Field Experience Scenario: If a technician installs the switch in a cabinet that is poorly insulated and exposed to direct sunlight in a hot climate, the internal temperature can exceed $60^\circ \text{C}$. The consequence is not immediate failure but a sharp increase in Bit Error Rate (BER), which manifests as intermittent, hard-to-diagnose communication glitches or complete network drops during peak heat hours. The correct remedy is to install cabinet cooling (fan or air conditioner) or relocate the cabinet.

6.2. Managing Electrical Fast Transients (EFT) and Surges

Industrial installations are prone to high-energy transients (voltage spikes) caused by inductive load switching (motors, solenoids).

• Protection Decision Matrix:
  • Condition: Switch is in a remote cabinet, far from the main panel, with long cable runs. Action: Install a separate surge protective device (SPD) on the 24 V DC input line and network line for the switch.
  • Condition: Switch is in the main panel with short, shielded cable runs. Action: Rely on the switch's internal protection, but ensure the power supply (e.g., PHOENIX CONTACT TRIO POWER) has robust transient protection features.
  • Technician Insight: A common mistake is to overlook lightning-induced surges. If outdoor cable runs are unavoidable, industrial-grade surge arresters for data lines are mandatory at the point where the cable enters the building or control cabinet.

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7. Deep Dive: Power Loop-Through and System Scalability

A key feature of the FL SWITCH 1108’s power terminal block is the ability to easily "loop-through" power, allowing the engineer to daisy-chain the 24 V DC supply to adjacent devices like I/O slices, interface relays, or other small switches without having to run a separate main power cable for each device.

7.1. Calculation for Power Loop-Through Capacity

When utilizing the dual $V^{+}$ and $V^{-}$ terminals for loop-through, the technician must treat the total current draw of all downstream devices as a single load on the main power supply wire feeding the switch.

• The Golden Rule: The total current for all devices connected via the loop-through terminals must not exceed the maximum permissible current capacity of the smallest component in the chain—specifically, the terminal block of the FL SWITCH 1108 and the cross-sectional area of the wire used.
• Example Decision: If the switch draws 0.2 A and three downstream devices each draw 0.5 A, the total current is $0.2 + 3 \times 0.5 = 1.7$ A. If the terminal block is rated for 6 A and the wire used is rated for 10 A, the loop-through is mechanically and electrically safe. If the wire was undersized (e.g., only rated for 1.5 A), a separate power feed would be required for the downstream devices to prevent overheating.

7.2. Structural Design for Future Expansion

When initially installing the FL SWITCH 1108, the system integrator should reserve a minimum of two unused ports.

• Future-Proofing Rationale: In automation systems, new field devices, temporary diagnostic laptops, or additional sensors are often added during commissioning or later upgrades. By reserving two ports and ensuring the total available power budget from the power supply is at least 25% higher than the calculated running load (Switch + all connected devices), the technician can facilitate rapid and seamless expansion without having to re-engineer the cabinet power and network layout. This prevents future emergency installations that bypass proper wiring practices.

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Note to Readers: This guide offers technical field advice based on common industrial practices. Always consult the official PHOENIX CONTACT documentation and local electrical codes prior to performing any wiring or installation work.

The author assumes no liability for any loss, damage, or malfunction resulting from the use or application of this information. Use is strictly at the reader's own risk.