EDITOR ’ S CHOICE TERMINAL BLOCKS
OEM
Choosing the correct terminal blocks for your requirements
WHY ARE TERMINAL BLOCKS IMPORTANT ?
Terminal blocks , also called terminal strips , are the backbone of automation and electrical control systems . These devices secure two or more wires together and are enclosed in insulated housing . There is a clamping component and a conducting strip . Terminal blocks come in a variety of sizes , specifications and colours .
Terminal blocks increase safety by grounding , isolating and protecting the other components in the electrical cabinet . They provide test points , adding functionality and safety to the circuit . They are finger-safe connections that prevent electric shock .
Using the correct terminal blocks for your application from the start protects expensive electronics and measuring devices . It provides your business with essential insurance against dangerous electrical situations , shutting down of production lines , and losses in manufacturing , productivity and customer confidence .
STRUCTURED TYPES OF TERMINAL BLOCKS
There are three structured types of terminal blocks :
• single-feed terminal blocks providing a wire-to-wire connection , connecting two wires together safely
• double-level terminal blocks stacking another level of connection terminal on the first one
• triple-level terminal blocks with three levels of contacts stacked on top of one another .
Multi-level blocks allow a number of connections to be made in the same block and can save space , simplify wiring and increase current capacity .
COLOUR CODING OF TERMINAL BLOCKS
This can get rid of the need for additional labelling . It can indicate to the end user :
• high current or voltage
• AC or DC input and output
• signal distribution wires or power distribution wires
• grounding and earthing .
CONSIDERATIONS IN CHOOSING THE RIGHT TERMINAL BLOCK FOR YOUR APPLICATION
Key considerations are type of connection , specification requirements , compatible accessories and rail length .
DETERMINE WHICH TYPE OF CONNECTION SUITS YOUR REQUIREMENTS
Different wire termination connections are used in different applications . They include push-in , screw-in , spring cage , insulation displacement and lugs .
Will there be vibration ( such as in shipping ) or long usage in the field ? If you choose a screw connection , you may have to write a torque specification and re-check the connection regularly . Push-in and spring cage connections do not need this .
Will there be high currents ? This could cause a spring cage connection to heat and cool regularly , weakening so that the wire is no longer safely anchored . In this case the spring should be steel reinforced .
Will the connection have repeated use ? How many times will it be required to operate and still make a reliable connection ? Insulation displacement connections cannot be continually disconnected and reconnected without cutting and shortening the wire , which wears out the blades . Push-in and spring cage connections have a limited actuation life as well .
DETERMINE SPECIFICATION REQUIREMENTS – SPACE
You should choose a terminal block and DIN rail that will fit well in the space you have , with enough clearance above and below for the terminals , accessories and the bend radius of the wires being connected .
Always make sure you have met the proper agency approvals for safety and end user location .
DETERMINE SPECIFICATION REQUIREMENTS – ELECTRICALLY
Consider the maximum voltage , current rating and the wire sizes used in your system .
The wire size can be calculated through the current rating . Wire size ( solid or stranded ) also depends upon the type of conductor being used .
The contact material of your terminal block and wires of dissimilar metals can corrode , and aluminium on copper will loosen if not properly treated . For a signal reading like a thermocouple , the metal of the terminal block has to match the metal of the wire in order to ensure an accurate measurement .
Review the physical environment as well as temperature ratings .
Consider maintenance requirements after installation . The actuation points to remove and re-attach wires should be easy to see and easily accessible .
WE ’ RE READY TO ASSIST YOU Invest some time in choosing the correct terminal block to ensure they are robust , efficient and perform well .
To choose compatible accessories to match your DIN rail requirements , click
here to find out more . We will also show you how to calculate DIN rail length .
As always , the Panel team at OEM Automatic is available to assist with your requirements and specifications . panel @ oem . co . uk | 0116 284 9900
22 PECM Issue 51