Reversing Switch – Types and Uses | A Quick Guide for Welders


A Reversing Switch is also known as a ‘Polarity reversing switch’ has four terminals that can be connected in pairs in two different directions to reverse the direction of the flow of current. There are different types of polarity reversing switches that are used for different applications.

One of the most common applications of this switch is seen in electric trains where the voltage is reversed that causes a change in the direction of the train to move in the opposite direction. It is made using a double pole double throw switch. Let us take an example where we take two wires.

  • Let wire A be positive and wire B be negative or wire A negative and wire B positive.
  • Let us take two more wires C and D for output to carry the desired power and here wire C is always positive while wire D is negative.
  • Now you feed power as input to the relay coil using a high reverse voltage diode.
  • The ‘TWO’ contact change is made in such a way that A switches to C and B switch to D when the inactive and A to D and B to C when it is in the active state.
  • This has caused an effect of reversing input polarity according to our requirements and conditions applied.
  • In an AC main supply, a bridge rectifier is used to reverse the polarity which constitutes a four rectifier diode.
The term ‘polarity’ is defined as the connection of the electrode to the terminals of a power source. It is mostly used when we use a DC power source. This is because, in an AC power supply, the polarity changes every half cycle on its own.

So, when the electrode is connected to the positive terminal while the workpiece is connected to the negative terminal, then it is termed as ‘Reverse Polarity’ or ‘Direct Current Electrode Positive’ (DCEP).


Generally, when there is damage in a massive power plant boiler, repairing it can last for months or even years and this can be maintained by using a strict timeline and follow guidelines. Let us now talk about an incident that took place at NAES Power Contractors in Cranberry, Pennsylvania.

They had an issue and had to run repairs on the inner tubing of the plant. This caused a replacement of 50 to 100 people who work on contracts in the boiler plant wall panels. These workers had two shifts 6 days a week.

It is based on the size and difficulty to reach each boiler part in the plant that makes the job tedious and time-consuming. The welders had to first climb a 24 x 24 hole and then crawl further into the pipeline area for them to be repaired.

No matter how hard it is to reach and work at a particular place in the boiler plant, the finishing and repair works must be on-point and of high-quality standards. This company generally deals with and repairs a lot of SA213 T11 material, which is a 1 ¼ chrome-built boiler tube that could have thicknesses to about 1 ½ inch.

They perform ‘Gas Tungsten Arc Welding’ (GTAW) which requires an arc electrode and a lot of shielding gas to facilitate the welding process. They also use ‘Shielding Metal Arc Welding’ (SMAW) in some cases.

Nowadays with the improvement in the variety and functionality of reverse polarity switches like the ‘XMT350 Field Pro’ that was manufactured by the ‘Miller Electrical Mfg. LLC’ which saves a ton of time for this welder as it has a single switch that can easily reverse the polarity.

  • Moreover, it changes the polarity instantly without any spots or marks leftover at the working spot.
  • The welders were able to do 10-14 welds per shift without any insane errors and the productivity just boosted up which was 5-6 welds per shift.
  • It estimated to 2 hours of work-time saved by the welders.
  • The welders need not leave the boiler plant to change the polarity and change the swap leads too.
  • The cable management was minimal and easy to undergo maintenance.
  • The major advantage of this equipment is the prevention of any accidental changes in the parameters and conditions of the ongoing process in the boiler by any other worker.
  • It saves a huge amount of time which in turn saves money because time equals money.
  • The major advantage that a worker/ contractor has been that he/she does not easily trip, slip, or fall while going outside the boiler plant to change the polarity or the parameters of the process.
  • Saving up to 10-20 minutes for a particular process for a welder can add up to several hours saved per day that one uses to change the polarity or other parameters.
Reverse Polarity
Reversing Switch

This is the image of the Miller ‘XMT 350 Field Pro’ polarity reversing switch unit.