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Disclaimer

Please note that this instructable involves working with high voltage mains and a mistake can be fatal. It should only be attempted by persons qualified to work with 415 Volt electrical mains.

This instructable is about how to build a manual three phase changer switch. It helps fight the common problem of Phase Cut in a three phase connection having single phase loads. (load is distributed over the three phases.) In residential connections fed with a 3 phase electrical supply, it some times happens that one of the phases gets blown out at the distribution transformer (due to uneven distribution of loads on the feeder or other reasons). There is also a problem of loose/ bad connection at the outdoor cable joint. In such cases, the loads connected to that phase in your home can be temporarily connected to one of the other two working phases. This change over serves this purpose. (Note: You should switch off other non-essential loads during this period, to avoid over loading the cables/ distribution transformer.)

It consists of three (single phase) change over switches, each connected to one of the three phases. The single phase loads are distributed over the three outgoing phase connections. Indication lamps are used to indicate which phase is on or off. There is additionally a voltmeter to measure the voltage.

The switches are wired as shown in the wiring diagram.

Step 1: Tools and Material

Following materials were used:

1. 1 cm and 5mm thick mdf board
2. 63 Amp, 4 Pole Changeover Switch (on-load type) - 3 (Its L&T make, model number was not mentioned anywhere.)
3. 63 Amp rated, 3 terminal Connectors - 2
4. 0-230 V Digital Voltmeter - 1
5. A toggle switch (for switching on/ off the voltmeter) - 1
5. Phase Indicator Lamps (R,Y,B) - 3
6. 7/20 Copper Wire - A few meters
7. Some length of Flexible Wire

Most of the components were purchased from local market. The Digital Voltmeter was sourced from Aliexpress.

Basic wood cutting tools like jig saw, drill machine etc. were used. Screw Driver, Pliers, Wire Cutter and Electrical Tape.

Step 2: The Frame

Using a few pieces of 1 cm thick mdf and 5mm thick mdf, create a frame for the change over switch. It will house all the components.

Mark the locations of changeover switches and other components and drill/ cut the board at required places.

Step 3: Fix the Components

I test fixed the components before assembling the frame, to check for proper spacing etc and to ensure that there is no mounting issue.

Then I built the frame. I fixed the change over switches, digital voltmeter, toggle switch, indicator lamps and terminal blocks. I also added small plastic spacers at the bottom and fixing brackets at the top. (this arrangement is specific to the location where this change over will be fixed. )

Step 4: Wiring Connections

Once all the fixing is done, we need to do the wiring. Refer the given wiring diagram.

Once the wiring is done, I thoroughly tested it with a continuity tester and test lamp. (Basic electrical testing rules apply.)

If the change over is being installed in an existing household installation, as in my case, you will need to do a few changes in the existing load wiring as well. Earlier, the three phases terminated on the 63 Amp load isolator and from there were distributed amongst loads. (using multiple miniature circuit breakers). Now since the change over is entering the picture, the outgoing of mains isolator would now terminate on incoming of changeover switch. The outgoing from the change over switch will then go to the MCBs.

Additionally, I checked what was connected to each MCB and then distributed the load in an equal manner amongst the three phases (approximately). (This was a precautionary exercise.) I then created three MCB groups, one for each phase. Then I labelled each outgoing MCB (load side) wire as to what load was it serving.

Last picture shows the final the device installed and working.

Cheers!

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