Terminal Blocks: Types and Selection Guide

What are Terminal Blocks?

Terminal blocks can be precisely defined as modular, insulated blocks that securely connect or terminate two or more wires. A series of terminal blocks in a long strip, together form a single unit of the most basic type of terminal blocks as shown in  Figure 1. The most basic application of terminal blocks involves connecting electrical wires directly to the ground, or to outlets and switches.

The wire contacting elements of the terminal blocks are usually made of moulded copper alloy, which has an expansion coefficient similar to that of the wiring material, to make sure there are no events of disconnection caused due to loosening of connections caused by different rates of expansion.

These expansion coefficients play a major role in safe and reliable connections of terminal blocks especially in Dubai, United Arab Emirates (UAE). Countries like the UAE have a desert climate, leading to extremely hot summers, added with the humidity of the Persian Gulf.  This is a highly corrosive environment, and terminal blocks can aid in reducing corrosion – but only up to a certain extent.

There are many types of terminal blocks used for different applications, often found connected in different combinations within control panel cabinets and enclosures, mounted on DIN rails as shown in Figure 2. You can find a few types of Terminal blocks in the terminal block section under the accessories category, at the Go Switchgear store.

A few advantages that terminal blocks provide are:

• Saving Space within cabinets and panels.
• Increase Safety – pr­­­­­­oviding safe and reliable connections and designs that prevent electrical shock to the operators.
•  Easy Installations – Current generation of terminal blocks can be clipped on and off a DIN rail very easily. You can also find these features on all the Elmex Terminal blocks available at the Go Switchgear Online webshop for Switchgear in Dubai, UAE.

There are many types of terminal blocks available in the UAE, based on their applications.

Based on Structure:

Single-level or single feed -through terminal blocks.

This is the most basic type of terminal block where there is one input contact and one output contact, both these have an internal connection that helps in connecting the wires together.

You can find the ELMEX single-level terminal blocks here.

Double level Terminal blocks or double-decker terminal blocks

They help in creating a bridge of connections between two levels, making the connections more flexible. These blocks can help in simplifying series and parallel connection, and simultaneously saving space.

Triple Level Terminals Blocks or Triple Decker Terminal Blocks

They are similar to double level terminal blocks but have an extra level which adds to the flexibility and can be bridged in the same manner as double level terminal blocks.

Types of Terminal Blocks based on Application and Device Type

• Earth Terminal Blocks (Checkout ET series by Elmex Controls Pvt Ltd.)
• Disconnecting Terminal Blocks
• Fuse Holders or Fuse Terminal blocks
• Power Distribution blocks
• Sensor/Actuator Blocks
• Thermocouple blocks.
• I/O blocks

How to Select the right Terminal Blocks?

Step 1: Select the right type of Terminal Block based on structure/application.

This step involves selecting the terminal block based on requirement — ­double level, single level, spring clamp, brass clamp or screw clamp and based on application— earthing, disconnections, and fuse holders,

STEP 2: Determine electrical specifications.

This is based on external and internal factors such as wire size, voltage rating and current rating. Wire sizes can be determined by their amperage ratings. The type of conductor (Solid or stranded) has to be considered in this step.

STEP 3: Accessories

Once the type of terminal block based on its applications and housing (Shallow or deep housing) is selected then supplementary additions such as end brackets, block covers, angle support brackets, blank marking tags and internal jumpers can be used based on the electrical design and requirements.

STEP 4: Rail length calculations

Factors that determine total DIN rail length to be used:

• the total density per foot of all the different types of terminal block and their respective quantities
• Half an inch for each rail end in order to accommodate the required rail mounting screws.
• 0.0008” or 0.2 mm additional tolerance per terminal.
• The width of the end covers, the end brackets, and any separators.

The designer or installer must always check with the local guidelines and certifications for using the right Terminal blocks. In the case of UAE:  DEWA, SEWA, AADC and ADDC are a few local and national certification and governing bodies to consult in order to verify brands and installation guidelines, not only for terminal locks but all your switchgear equipment.

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