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Electric Phase or Line Tester – Construction & Working of Mains Tester

Phase or Line or Electric Mains Tester – How it Works?

What is Phase or Mains Tester?

Phase, electric mains or line tester is a basic tool which is used to test and identify Phase / Live/ Hot or Positive (+) wire / conductor in electrical installation also known as voltage or current detector.

Phase or Line Tester is also called Neon Screw Driver or Test Pin.

Good to Know: Phase, Line, Hot, Live and Positive are the same terms used for single item.

Construction of Phase or Line Tester

Following are the main parts of a typical Phase or Line Tester.

Internal Parts of a Phase Line-Tester
Internal Parts of a Phase Line-Tester

1). Metallic Rod and Mouth

It is a cylindrical metal rod. The flat end (mouth) is used as a screw driver or touch electrical conductors/wires to find phase or live wires and the other end is connected to the resistance, neon bulb, element and metallic cap screw respectively. The flat end of cylindrical metal rod is also covered with transparent insulated plastic for insulation proposes except mouth.

2). Body and Insulation

All these components (Resistance, Neon bulb, Element or metallic spring, and Metallic Cap screw) are covered in a transparent insulated body which made of plastic. The flat end of cylindrical metal rod is also covered with transparent insulated plastic for insulation proposes except mouth.

3). Resistor

Resistor is an element which opposes the flow of current through it. In a phase or line tester, resistor is connected between cylindrical metal rod and Neon bulb to prevent high current and reduces it to a safe value to protect the neon bulb. Without a resistor, high current may damage the neon bulb. Moreover it  may be dangerous to use this tool without resistor.

4). Neon Bulb

Neon bulb is connected between resistance and element (metallic spring). It is used as phase indicator bulb. When a small current flows through it, the neon bulb starts to glow. Due to neon bulb, a phase or line tester is also called a Neon Screw driver.

5). Element (Metallic Spring)

Element (metallic spring) is used to make connection between neon bulb and metallic cap screw.

6). Metallic Cap Screw and Clip

Metallic cap screw is used for to tight all the components inside the phase tester slot. In addition, metallic cap screw is connected with spring (element) and spring (element) is connected with neon bulb then. Moreover clip is used for holding the phase tester in pocket.

How does an Electric Phase or Line Tester work Construction Working of Mains Tester
Construction Working of Mains Tester

Working of a Phase or Line Tester

When we touch mouth (flat end of the metallic rod) of phase or line tester with naked Live / hot wire whereas one of our finger touch the metallic cap screw or clip of Phase/Line Tester, then circuit is completed and current start to flow in metallic rod, Hence the neon bulb inside mains tester glows.

Metallic rod is connected to the resistor which reduces high current to a safe value. The reduced current passes through Neon bulb which is connected to (metallic spring). Metallic spring is connected with metallic cap screw which is in contact of our fingers. A very small current passes through our body to earth and complete the circuit. When circuit is completed, current starts to flow and the filament of neon bulb starts glowing. This indicates that the touched wire with Phase / Line Tester mouth is Phase / Line / Hot.

If we perform the same action as mentioned above, and Neon bulb does not glow, it means that is a Neutral (-) Wire/Conductor or there is no mains supply in the phase wire or phase wire is broken in the middle.

Using Phase Tester as Line Indicator
Using Phase Tester as Line Indicator

Safety Precautions

  • Never try to work on electricity without proper guidance and care.
  • Work on electricity only in presence of those persons who has good knowledge and practical work to deal with electricity.
  • Don’t touches the open wire/Conductor even tester shows absence of phase or hot supply.
  • Use Line Tester only with 100V-500V.
  • Don’t use Phase or Line Tester with High voltages.
  • Don’t hit on the handle of Line tester otherwise, Neon bulb or element may damage.
  • Doing your own electrical work is dangerous as well as illegal in some areas.Contact the licensed electrician or the power supply company before practicing any change in electrical wiring connection.
  • Electricity is our enemy, if you give it a chance to kill you, Remember, they will never miss it. Please read all caution and instruction while doing this tutorial in practical.
  • The author will not be liable for any losses, injuries, or damages from the display or use of this information or if you try any circuit in wrong format. So please! Be careful because it’s all about electricity and electricity is too dangerous.

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  1. It is a cylindrical metal rod. The flat end (mouth) is used as a screw driver or touch electrical conductors/wires to find phase or live wires and the other end is connected to the resistance.

  2. am so much excited after reading your blog. Your blog is very much innovative and much helpful for any industry as well as for person.High Voltage Testing

  3. Dear sirs.I read one of u r article about Line tester with nice details.Easily we can understand how it works, what r all its inside parts etc in a simple&legible way. Tnx for it..Now I request u to kindly send one WIRING DIAGRAM of a ROTARY swtch of 4 ;points suitable for a Philips Mixie grinder motor wires of 3 speed with one incher switch&Overload connection&line indicator etc.After changing the line indicator bulb I am confused of fixing the power&motor winding wires in the rotary switch.my mixie is Philips 230Volts A.c -600 watts3 speed rotary switch ith incher switch&line indicator.Kindly send me correct wiring diagram for switch&motor wires&powerchord etc by my email given above..tnx chandran(Retd Engineer)28-1-15one yellow wire.one green wire.one black wire are seen from motor to rotary switch….

      1. One of my small tablefan PRIYA without capacitor&Oscillations run nicely but getting heated soon though working.How to prevent getting heated the fan for running continuously without getting heated220V an single phase induction motor only with 5 leafs of plastic just like”WILSSON” etc Delhi make.Plz advice soon by my email as I am a regular reader in email of u r articles. Thanks (ACN)14-10-16

  4. we rgetting useful day to day electrical technology information in a simple&lucid manner by email.Tnanks (acn)

  5. what if we have no contact with earth, or we are standing on a very good insulating material?
    will the glow get reduced when testing low voltage??
    What is the maximum voltage that this type of tester can detect?

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