TERMINAL BLOCKS-PART 2(INSULATION HOUSING)

Hello everyone!,

Let's learn something about Automation and control.
Check out my site: www.electricalmaniacs.blogspot.com

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