More about terminal blocks

Terminal blocks come in different shapes and sizes and with the advancing technology,different kinds of terminals with different capabilities are developed.In the previous post we saw the clamping systems of the terminal blocks.Now that we know what the terminal block is and about its construction and why is it constructed in the way it is constructed,we can move on to its types and categories.The Terminal blocks are used for transferring the current ,so obviously they have the current ratings ,with that comes the voltage rating,then as the construction suggests the wire also needs to put in according to the cross section.

TERMINAL BLOCKS-PART 4 (CLAMPING TECHNOLOGIES)

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In the previous post we were talking about the metallic parts of the terminal blocks out of which one of them is the current bar. Up till now we have seen the insulating part and the conducting part of the terminal bock,but we forgot to think about one thing that how will we hold the wire in place (definitely not soldering !).

So how?!.

The wires need to be in complete contact with the current bar for the maximum output,now in order to do that we need something to hold the end tightly. Now this is where the third metallic part of the terminal block comes into play.It is called the conductor clamp.

Let's break this word up into two parts first conductor means that it is made up of conducting metal and the "clamp" means to hold something together tightly.So by this word only you must have understood that this is a very important part of a terminal block.Mind you clamp is not a name its a principle.They come in different shapes and sizes.Clamping is also known as termination so terminal blocks may use one of several different methods to achieve wire connection.

Let me list out some of the most used and basic clamping technologies:

1. Screw clamp-Steel.
2. Screw clamp-copper alloy.
3. Screw clamp Spring loaded.
4. Spring clamp.
5. Stud and nut clamping for cable lugs

Brief description:

• Screw clamps use a screw to tighten the wire and make an electrical connection and are the classic, industry standard termination method. This type can accommodate a very wide range of wire sizes and provides a reliable connection. 
• Spring clamps use the force of a spring to retain wire clamping. They represent a newer alternative to screw clamps and are particularly useful in applications using small wire diameters and limited working  space.
• Insulation displacement connections (IDC) push the wire between two sharp pieces of metal, allowing a connection to be made without exposing any bare wire.
• Tab connections are designed to be inserted and removed rapidly without the need for soldering. They are also known as spade or blade terminals.

Detailed Explanation:

The dimension of these current carrying parts varies in regard to the amperage/wire size and the construction of the block itself. Depending upon terminal block layout, wires can be clamped in position using screws, a combination of screws and pressure plates, wire cages or spring clamps.

 A screw is the easiest method of connection: A screw is utilized to secure the wire against the current bar. With screws and a pressure plate, the wire is constrained with a metallic plate, which fastens the wire when the screw is secured. The drawback of this method is just that whenever these terminals are subject to the vibration , there is a possibility of disconnection of wires.

Screw clamp technology

Next comes the screw clamp spring loaded clamping technology,now the only change in this is the addition of the spring under the screw clamp.This technology comes after the normal screw clamp terminals had problems working in places where vibration is more prevalent like in cement ,oil and gas etc.

Screw clamp spring loaded technology

With a wire cage, when the screw is tightened, a cage pulls upward and squeezes the conductor against the current bar. The large contact area provides exceptional contact properties. Because the screw does not have immediate contact with the conductor, wire damage is prevented.Even thin stranded wire can be connected without the use of additional Ferrules or wire pins.

 Spring clamps require a tool to open. The clamp encloses the wire to provide dynamic clamping. This extra holding action endures vibration.Spring clamps are the best of the lot.Still some people are still using the other technologies cause they cost you a wee bit more.

There are many companies that make terminal blocks such as Phoenix contact,Connectwell,Weidmuller,Mouser,DigiKey,Allen Bradley,Schneider Electric,Altechcorp etc

So that's it for this article ,in the next one we will cover the categorization of the terminal blocks.

Till next time!!

Bye!

TERMINAL BLOCKS -PART 3(CURRENT BAR)

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In the previous post we learned about the insulated part of the terminal block/strip.Now its time to learn about the metallic parts of the terminal block.Basically in the last post we decided on the insulation of the terminal block,now for the ease of connection each wire needs to be connected separately and marked separately so that the engineer can properly identify it and he does not waste time in searching for the right connection.

You'll say that "In control cabinets space saving is our major concern!".That is definitely correct , but the width of the terminal blocks nowadays of taken very seriously.I can assure you that space saving would not be of your concern.Now getting back on the topic , we will be discussing about the current bar.

Before going into technicalities let's first try to understand why the current bar is used .Continuing from our previous post we have decided what kind of insulation housing our terminal block needs to have,now there are two ends in a terminal block from where the wire ends are terminated.Now those wires are terminated on the extreme ends of the terminal block and the body of the terminal block is non conducting so we need a conductor in between for the transfer of the current.So some conducting metal strip,could be used.Now a question arises that one of the problems that led to the invention of the terminal blocks was corrosion,so if we use metallic parts again wouldn't that lead to corrosion .

Before talking about corrosion let's talk about what kind of metal can be used for the current bar.Iron,Steel,copper,silver etc are some that come to the mind.All of them have their own set of advantages and disadvantages.Like silver is the best , but cost is too much high etc.So we go for copper (but even copper can get corroded??),so copper alloys are used in the making of the current bar.

Now that we have decided about what kind of metals we are gonna use.Let's see even copper alloys can succumb to the harsh environment.So we need an additional contingency plan to counteract corrosion effect.That naturally would be plating.

Now if plating ,then of what kind?,Which metal shall we use?,does that particular metal have any disadvantages?,will it protect the terminal block in all kinds of atmospheres? are some of the questions that pop into our mind.

Electrolytic copper or copper alloy current bar is usually coated with tin with a nickel undercoat.Now the nickel undercoat is due to the fact that if tin directly comes in contact with copper , then it reacts with it and zinc migration*effect takes place which is undesirable.

*In zinc migration the reaction produces zinc and this zinc gathers at one place thus neutralizing the effect of plating.

So ,basically the current carrying bar must have such a form that the conductor has a strong contact area in the connection point. Current bars are made out of brass / electrolytic cooper. Coating of tin/lead oxide, nickel while ensuring surface protection guarantees very low contact resistance.Low contact resistance is really a must property in the current bar as we always want maximum output.The thickness of the current bar varies according to its current carrying capacity i.e the more the capacity more thick the current bar.The Current bar is one of the two metallic parts in a terminal block.We'll take the other part in the next post.

There are many companies that make terminal blocks such as Phoenix contact,Connectwell,Weidmuller,Mouser,DigiKey,Allen Bradley,Schneider Electric,Altechcorp etc

Till the next time!

Keep asking why?!

Bye...

TERMINAL BLOCKS-PART 2(INSULATION HOUSING)

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Let's learn something about Automation and control.
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Electrical terminal blocks are used in connection with switchboards,control circuits for switching apparatus and similar electrical circuits.Particularly in the electronic and the automation equipment field,the demand is arising for terminal blocks.The topic of terminal blocks is unknown to the most of electrical engineering students (cause the topic in itself is very small).Learning about terminal blocks has been a terrific experience for me.It has opened new avenues of learning practices which is unthinkable.

Now, the topic for today is further insight on terminal blocks.They occupy quite a lot of space in a control cabinet.Our goal or objective is to minimize the space utilization,but at the same time we need the best results.Let me tell you a short story about Sam.Sam was an employee of a electrical company,which made control cabinets ,now this was the time where there were no terminal blocks.So in order to terminate the circuits , soldering was used .Sam was getting  a lot of complaints from his customers,about difficulties they had in the maintenance work and also during troubleshooting.Other problems were the effect of atmosphere on the exposed metallic components.These were some of the many problems that were faced by the customers and these were quite serious problems.So Sam started looking for a way to fix this.
He had to fix three problems

1. Corrosion.
2. Ease of connection.
3. Quick identification during troubleshooting and maintenance. 

So, now that he had listed all his problems,he started looking for possible solutions to his problems.First of all his problems was corrosion ,so he needed to cover the exposed ends of his wires (which were connected to the other wires,termination points to be specific).Also,the covering should not have a conducting property(otherwise all this would be of no use at all).So after researching various insulating materials he zeroed in on the plastics as they are fully suited and cost effective.Also he needs the plastic to have a good tensile strength,it should be able to withstand higher temperatures (as control cabinets are basically in a closed condition and there are a lot of wires coming in and out and there is a lot of heat).Also the plastic should have good impact resistance,resistance to fuels,acids and oxidizing agents(anything can happen)!.Two kinds of plastics were zeroed in 

1)Thermoplastic.

2)Thermosetting.

• A thermoplastic is a material, usually a plastic polymer, which becomes soft when heated and hard when cooled. Thermoplastic materials can be cooled and heated several times without any change in their chemistry or mechanical properties (seems quite ideal,hun!).

So,here in this group he decided Poly amide 6.6 was the perfect fit.It had all the "good" properties you would expect from a insulating material that is to be used in control equipment.Mainly it could withstand temperature up to 105 degree Celsius. Also,its electric properties like resistance to surface discharge with CTI*>600(this is according to IEC-60112).Now the surface discharge is a very important property the insulating material should not have a electric breakdown.

*CTI is known as Comparative Tracking Index which is used as a measure for measuring electrical breakdown.

Now the polyamide 6.6 can help you only upto a certain temperature limit,in big industries the temperatures go even beyond that(every material has its limits).So Sam thought "which kind of plastic can go even further in terms of its characteristics or properties?".Thermosetting plastics were the solution.Let's first understand what thermosetting plastics are. 

• Thermoset, or thermosetting, plastics are synthetic materials that strengthen during being heated, but cannot be successfully remolded or reheated after their initial heat-forming. This is in contrast to thermoplastics, which soften when heated and harden and strengthen after cooling. They are liquid or malleable at low temperatures, but which change irreversibly to become hard at high temperatures.

Melamine was chosen from the group of thermosetting plastics (generally known as aminoplasts).It has excellent resistance to deformation (at real high temperatures           Polyamide 6.6 suffers from deformation),particular hardness and a very good surface brilliance.It does not ignite and gets converted into char form in case of a fire.It is also abrasion and chemical resistant and waterproof.

Melamine is usually preferred in severe environmental conditions and is preferred for circuit breaker panels,refineries,chemical plants,potentially explosive installations and any other high risk environments in general.

Due to all those advantages there is also a high price to pay,much more than polyamide terminals but it usually depends on the customer.

//Just something in between"what if both the polyamide 6.6 and melamine are of same color?"The melamine is a little harder than the polyamide,also it is kind of brittle(i.e it can break into pieces,if you throw it just don't do it!!),tap on both the surfaces and you will find polyamide emits a much deeper sound than the melamine.Also Melamine is heavier than polyamide.//

• Ceramic is an exceptionally rugged material that can be utilized in extremely high temperatures approaching 250 degrees Celsius. Ceramic blocks can also operate in industrial plants with excessive dust deposits and abnormally corrosive atmospheres

Ceramic is also an option for the insulation.It is not used much now a days,but there are certain places where you don't have a choice.It is the most heaviest of the lot.

Insulation materials must be non-flammable and self extinguishing.For this there are various classes in which polyamide 6.6 terminals can be divided into:

1. V0 class:The specimens may not burn with flaming combustion for more than 10 seconds after the application of the flame. The specimens may not have glowing combustion that persists for more than 30 seconds after the second removal of the test flame.
2. V1 class: The specimens may not burn with flaming combustion for more than 30 seconds after either application of the test flame.The specimens may not have glowing combustion that persists for more than 60 seconds after the second removal of the test flame.
3. V2 class:The specimens may not burn with flaming combustion for more than 30 seconds after either application of the test flame.The specimens may not have glowing combustion that persists for more than 60 seconds after the second removal of the test flame.

These classifications are given by Underwriter Laboratories.The description given here is in brief,but enough to understand the three classifications.

This is the story about how Sam got rid of his problems by deciding on the type of Insulation housing.Thus we come to point our first part of the terminal block "The Insulation Housing".

Next we will take the metallic parts of the terminal blocks.

Till then see ya!!

Keep asking why!

Bye...

There are many companies that make terminal blocks such as Phoenix contact,Connectwell,Weidmuller,Mouser,DigiKey,Allen Bradley,Schneider Electric,Altechcorp,Wago etc

Terminal Blocks-Small,but important...

Since the starting, we have always been trying to simplify our lives (in doing so making it more than complicated for us electrical engineers!). By this I mean , the rise of AUTOMATION in the industries.

Now, what is the meaning of AUTOMATION.?

"The creation and application of technology to monitor and control the production and delivery of products and services.”

//Umm... looks like you are interested,if yes then check this out:

If y'all haven't read the previous post click on the links below:

1)https://electricalmaniacs.blogspot.in/2017/09/electrical-control-panels- interesting.html
2)https://electricalmaniacs.blogspot.in/2017/09/detailed-study-of-electrical-control.html//

So, according to this automation is something that makes human involvement lower to an extent(makes life easier,hun!).If you venture a few years back then you will see that the percentage of workers working in a factory was much more than what it is now.Previous mechanical control is now replaced by electrical and electronics control.The control panels are how we control the machines working in a factory.Control panels are the combination of a lot of parts(both electrical and electronic) cramped in a box(cause we are always optimizing everything!).

If you have a little idea about panels and have seen them,then you would know that in the primitive control panels,for termination the wires used to be soldered together(which was too much messy and dangerous).Also there are a lot of small to big components ,out of which a lot of big and small wires are coming in or going out.So, the point is it becomes very difficult to differentiate.Also if there is a problem then you have to desolder and the repeat the process again (get's tiresome).

Enter the terminal blocks...

Introduction:

• What are they?

Terminal blocks function as convenient connection points for electrical wires while avoiding the need for wires to be spliced together.As seen earlier control panels consists of a huge bunch of wires,and so to make our life easier terminal blocks are used for wire termination in the control panels.With the technology rapidly advancing day by day,different types of terminal blocks were developed.

• Where are they used?

Anywhere and everywhere ,where automation is used.Automation consists of control panels and control panels consist of terminal blocks.So , basically we are talking about almost every industry the market has to offer.

Specialized functions include:

Shunt points for test voltage or current,commutation or inversion,disconnection,grounding etc.

• So,what advantages do they offer?

• Easy and hassle free installation.
• Easy recognition.
• Easy and complete interchange capability.
• Addition of new elements if necessary.
• Higher system safety.
• And many more..(but these are the most basic ones).

• What do they look like?

At the most basic level a terminal block is a strip of molded plastic fitted with metal plates and screws. Each connection point (terminal) features a metal plate and two parallel screws which conduct electricity and secure the wires in place.

Let's see a picture

Fig:One of the most basic designs of terminal blocks(screw type)

History:

In 1982, Phoenix Electric Company invented a modular terminal blocks of the world's first, and then laid the prototype of the modern terminal blocks.Now, there are many companies like Weidmuller,ABB,Eaton,Wago etc.

In our next post we will discuss more details about terminal blocks.

Till then BYE!!

Stay Cool!

Keep asking why?!!