What Is a Test Pen? Types and Selection Criteria

A test pen is a screwdriver-shaped test tool whose handle lamp shows whether voltage is present when the tip touches a conductor; it does not measure the voltage.

A test pen (voltage tester screwdriver) is a screwdriver-shaped test tool that shows with a lamp in its handle whether voltage is present when its tip touches a conductor. It is used to find the phase terminal in sockets, switches and terminal blocks, or to see which points of a vehicle's wiring battery voltage reaches. A test pen is not a measuring instrument: it does not show the value of the voltage and does not prove on its own that voltage is absent.

Types

• Electrical (mains) test pen: The classic neon-lamp type. The user touches the metal cap at the back end of the handle; a small current passes through the pen and the body to earth and lights the lamp. It is made for mains installations.
• Automotive test pen: Lights its lamp from the vehicle's battery voltage. Its lead is connected to the vehicle chassis to complete the circuit. It is not used at mains voltage.
• Electronic and non-contact detectors: Although pen-shaped, they are a separate group, listed under Voltage and Continuity Testers.

Selection criteria

1. Installation: Choose the electrical type for mains and the automotive type for vehicles; one does not replace the other.
2. Voltage range: The operating range printed on the pen must cover the installation to be tested.
3. Tip type: The pen also turns small screws. Choose a flat tip for terminal screws and a Phillips tip for cross-head screws.
4. Length: 135 mm suits pocket carry; 190 mm reaches deeper terminals and further into a panel.

Common mistakes

• Taking an unlit lamp as "no voltage": Insulating shoes, a ladder or gloves, a finger not touching the metal cap, or a faulty lamp can keep the lamp dark even when voltage is present.
• Ignoring a lamp that lights on neutral: In a sound installation the lamp does not light on the neutral terminal. If it does, the neutral may be broken or the wiring mixed up; check with a measurement before touching the circuit.
• Making the pen the only verification tool: Before working on a circuit, the absence of voltage is verified with a two-pole voltage tester. The tester is tried on a known live source before and after the check.
• Using a pen with a cracked body: A pen whose body or lamp window is damaged does not keep its insulation; replace it.

Standard

Requirements for two-pole low-voltage testers are set out in IEC 61243-3. A single-pole test pen is not covered by this standard.

Test pens in the catalog

The Test Pens category lists 6 active products (October 2026):

To read the value of a voltage, see Digital Multimeters.

Frequently asked questions

Does a test pen prove that there is no voltage?

No. An unlit lamp can be caused by the user standing on an insulating surface or by a faulty lamp. The absence of voltage is verified with a two-pole voltage tester.

Why does a test pen light on the neutral line?

It does not in a sound installation. If the lamp lights on neutral, the neutral conductor may be broken, phase and neutral may be swapped, or the line may have a leakage.

Can an electrical test pen be used on a vehicle?

No. The neon lamp does not light at the low voltage of a vehicle's wiring. For vehicles, use an automotive test pen connected to the chassis.

Should I choose 135 mm or 190 mm?

135 mm is enough for sockets and switches. Choose 190 mm when you need to reach deep terminals inside a panel.