Electrical Panel Connectivity

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Terminal blocks & connectors electrical and control panels to the outside world.

Much of the focus of electrical and control panel designers is on selecting, arranging, and protecting internal components. After all, locating power and automation equipment in the field, close to the loads and devices they serve, is the main purpose.

However, it is also important to properly select, design, and install components to make associated electrical connections. Even though wireless is becoming popular for certain types of communications, it is often still necessary to connect electrical wires using terminal blocks or other connectors.

Whether for commercial or industrial use, these panels and the associated connections can be in harsh environments, with extremes of temperature, liquids, chemicals, vibration, and more. To ensure that the electrical interfaces between panels and field wiring perform reliably for the long haul, panel designers need to consider the best connectivity options. Terminal blocks, connectors and interface modules are the basics worthy of attention.

Classic connectivity: Terminal blocks

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Figure 1. Push-in design terminal blocks are available in many configurations with a variety of connection technologies that reduce wiring labor compared with traditional screw terminals.

Terminal blocks have long been the standard way for landing field wires—both individual conductors and multi conductor cables—into a panel. But that does not mean there has been a lack of innovation for this termination style. The major terminal block connection technologies (shown in figure 1) are:

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Screw terminal. This traditional technology uses screws, with or without pressure plates, to terminate wires directly or via a crimp lug. A wiring cage can compress on bare wire or a ferrule, or a ring or fork lug can be connected to the wire and inserted under the screw. Users must torque the connection properly to ensure a long-lasting, positive connection. To prevent the wires from loosening over time, some manufacturers have designed the structure to lock the screws in place and be maintenance-free. The screw terminal method is universal, recognized globally, and can handle the widest range of wire sizes.

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Spring clamp. This technology uses spring force on the conductor to provide maximum contact reliability, even in high-vibration environments. A tool, usually a screwdriver, is needed to push open the terminal points as the wire or ferrule is inserted, but completing a termination is faster and easier than it is with a screw terminal. This type of connection is beneficial to use in high-vibration environments such as railway and marine applications.

Users must also consider what functional arrangements are needed. These could include:

·Feed through, the most common and simple type of terminal block. It is single level and provides one wire-to-wire connection. Some types have multiple connections for one-to-two or two-to-two connectivity.

·Multilevel, which is like the feed-through style, but with two, three, or more isolated levels stacked together for substantial space savings.

·Grounding, where the terminals are electrically connected to the DIN rail or panel on which the terminal is mounted. This provides a ground connection, without having to purchase and install a separate ground wire.

·Disconnect, which is like the feed-through style but incorporates a knife switch to easily open (disconnect) the circuit without removing wires.

·Fused, which is like the disconnect style, but the switch houses a fuse for downstream circuit over current protection. It may also include an

LED blown fuse indicator for troubleshooting convenience.

·Sensor/actuator, which is like the multilevel style but may also include a grounding connection. This is especially suitable for common multi conductor cable wiring that is often used for connections with sensors and actuators.