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What is the purpose of the Main Switch?

The Main Switch is the one part of a control panel which has a large impact on progressing a project, and applies or disconnects the power of the control panel.

We’ve already covered some of the important aspects of a control panel, but some might say that what we’re going to cover today is the most important of all. The electrical Main Switch is the one part of a control panel which has a large impact on progressing a project. Learn more about the purpose of the Main Switch below.

When we look at the panel from the outside, one of the first things we see is something labeled the Main Switch sometimes called an isolator.

What it does essentially is applying or disconnecting the control panel from the power source.

The control panel we have here is powered by a 3 phase supply, which is rated at 415 Volt AC.

This, in turn, can be used within the panel to power single-phase devices, or 230 Volt AC by using 1 phase of the 3 phase supply.

We can also use transformers to convert AC voltage to DC voltage to power our 24 Volt and 12 Volt devices we briefly covered in the Control Panel overview video.

So the main switch applies or disconnects the 3 phase power that we have in the control panel.

3 phase labeling system

We usually designate the 3 phases with the following labeling system; 

L1, L2, and L3 are the 3 phases of the supply.

N is the neutral wire. The neutral wires’ purpose is to provide a path back to electrical ground to complete the circuit.

When we put the main switch in the  position, it indicates that the isolator is in the OFF position; and it will disconnect the power flow to the control panel.

When we put the main switch in the 1 position, it indicates that the isolator is in the ON position; and it will enable the power to flow to the control panel.

On the back of the door, this switch has wires connected to the terminals on the switch. You see the identifiers on the cable L1, L2, L3, and N.

These are connected to the main power coming into the cabinet labeled L1, L2, L3, and N also.

3 phase power distribution

The other side of the switch connects to the distribution unit. One of the phases goes to power the power supplies; one phase goes to the input for the 24 Volt DC power supply, and for the 12 Volt DC power supply.

The input to these two power supplies can be 100-240 Volt AC. The power supplies transform the AC signal into a DC voltage output, 24 volts, and 12 volts. This DC power can then be used for devices in the control panel, or for devices out in the field too!

Since we are using 1 phase of our 3 phase supply, our input to these two power supplies is around 230 Volt AC.

The rest of the 3 phase power goes into terminal block and can be used to power the devices that work with 3 phase power.

So the single-phase power, powers the supplies and we connect the 3 phase power to the terminals; So that we can use them with devices that work with a 3 phase supply.

When we install the control panel in the field, the 3 phase supply will be connected to the top of these terminals. Then through the trunking, they are going to be connected to the top of the main switch.

Through the other end of this switch, the terminal blocks are going to be connected to the terminal block.

One phase power the power supplies and then all of the 3 phases also will be connected to the terminal block; So that we can use them to power the devices that work with the 3 phase supply.

We have the 3 phase supply connected on the bottom and the devices can be connected to the top of the terminal blocks.

If we put the main switch to the 0, the incoming 3 phase supply power will be disconnected, and that shuts down the whole control panel, including all of the devices that work with 24 Volt DC and 12 Volt DC, and also the devices that work with 3 phase power.

Summary

So to sum it all up, here is what we learned in this article:

– When we look at the panel from the outside, one of the first things we see is something labeled a “Main Switch” sometimes called an isolator.

– The main switch applies or disconnects the 3 phase power that we have in the control panel.

– We usually designate that 3 phases with the following labeling system; L1, L2, and L3 are the 3 phases of the supply. “N” is the neutral wire. The neutral wires’ purpose is to provide a path back to electrical ground to complete the circuit.

– The output of the main switch connects to the distribution unit. From there one of the phases goes to power the power supplies, and also goes into terminal block.

– The input to power supplies can be 100-240 Volt AC. These power supplies transform the AC signal into a DC voltage output, 24 volts one case, and 12 volts on the other. This DC power can then be used for devices in the control panel, or for devices out in the field too!

– The 3 phase power that goes into terminal block can be used to power the devices that work with 3 phase power.

– When we put the main switch to the ‘0’ position, the incoming 3 phase supply power will be disconnected, and that shuts down the whole control panel, including all of the devices that work with DC power, and also the devices that work with 3 phase power.

That’s it for this article! We are starting to get into a bit more detail about the inner workings of the control panel now, and thanks for staying with us so far! If you’ve understood everything we’ve covered so far, you are now well on the way to having a great understanding of how a control panel works, add to that now the main switch function, and why we use them, you’ll soon be powering on your future!

This article was brought to you by RealPars in partnership with Pro-control in the Netherlands.

They are experts at control system design and industrial automation. They have a team of world-class automation engineers and have been designing and implementing industrial control systems in different industries for many years.

If you want to get in contact with them, you can check out their website at pro-control.nl.

Got a friend, client, or colleague who could use some of this information? Please share this article.

The RealPars Team

By Shahpour Shapournia

By Shahpour Shapournia

CEO, RealPars

Posted on Nov 25, 2019

By Shahpour Shapournia

CEO, RealPars

Posted on Nov 25, 2019

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