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Will a 110v pen tester pick up or test a 220v socket? It doesn't sound or light up near the 220 socket. I want to make sure it works before I replace it.

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    You're talking about a non-contact type voltage dtector, right? – ThreePhaseEel Jun 13 at 17:34
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Test Before and After

Always before and after using these detectors, try them on a known working live circuit. Plug in a light or so to confirm the circuit.

For the voltage range, check the manual or labeling. Usually applying a 220V/240V to a 120V tester should pose no problems, but at voltages above about 500V (not your case) there will be safety issues.

There are two kinds of "pens", both are safe.

Contact Tester

The first one, an older design, is a passive tester with a single metal tip to make contact with the wire being test. It often serves a dual purpose as a detector & screwdriver. When making electrical contact with the live wire, a closed circuit is formed through the user. If a strong enough voltage is present (perhaps 90V to 1000V) a weak and safe current will flow through its built in ballast resistor and a little built-in neon light, thus energizing the light, and flowing back through the ground.

The light is energized by the live wire being tested, and no batteries are needed. The operational range is limited, usually the specified voltage and not less. There is no electronic amplification circuitry inside.

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Non Contact Voltage Tester

The second one, a non-contact voltage tester, serves practically the same purpose but it is far more sensitive.

It needs no electrical contact with a conductor to sense a live circuit, and so it can detect a live wire through the wire's insulation.

Its tip is insulated (plastic) and contains an antenna for picking up weak electromagnetic fields at the mains AC frequency. It can operate on a wider range, say 12V or 50V up to 1000V. It has electronic amplification circuitry inside, and requires a battery to operate.

This type of voltage tester is different from non-contact clamp-on probes for sensing and measuring currents flowing through a wire. The non contact voltage tester does not require a current to flow to detect whether a wire is live.

If this is your kind of tester, it should work on a wide range of voltages, including 120V and 240V, and AC mains frequencies, including 50Hz and 60Hz.

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Receptacle Tester

Both types of above pens only work on the live. They do not detect the presence of a neutral or ground wire. For this you need a receptacle tester.

When they might not work

The first one, the metal tip tester works with a resistive or capacitive path to ground. It will work for instance through thin rubber shoes, but when standing on a wooden ladder there's likely not enough capacitive coupling between the user and the ground to allow the small current needed to light-up the bulb.

A ground path that is too weak or moisture inside the pen may cause a malfunction.

The second one, the active tester with an antenna, does not require a closed circuit through ground and operates even if the user is on an insulating ladder (fibreglass, wooden) or otherwise well insulated from ground.

But a broken tip may disconnect the antenna, water ingress may damage the electronics, and a failing battery of course also prevents operation.

Often the tip of the pen is a flat head so it can also serve as a screw-driver and provide a warning if the screw (and its connected wiring) is live.

The best way to check the function of the pen tester is to try it out on a known live circuit. If the light glows (screwdriver) or the tester beeps (non-contact), it works. If it doesn't and you are sure the circuit is live, because you have something plugged in, it is failing.

These pens will usually fail safely, meaning that a malfunction of the light or other internals will not expose the user to dangerous currents. As a general rule, keep them dry and protect them from mechanical cracking and chemical corrosion.

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    Was a story a few days ago about a recall for some Klein voltage testers. Seems like the button sticks/does not work on some and gives no voltage reading when there is voltage. Not sure if I could post it on here. – crip659 Jun 13 at 22:13
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    I agree with, test-check-test (osha requirement) I use a fluke brand but have used Kline and many other brands over the years and I test before and after to make sure the the non contact tester is working. Pushing a non contact into the receptacle should show a live circuit. I test even with my fluke that flashes every second or so when it’s on. I have no connection to fluke other than owing there products high priced but they last some even after going swimming (not recommended). – Ed Beal Jun 14 at 15:00
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    @EdBeal yes before and after, I edited. Also included the important point you make on water: non-contact may not operate and give false negative, contact tester may expose dangerous voltage/current. I think all this is way more than the OP asked for, but it's hopefully a useful read for others. – P2000 Jun 14 at 17:38
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    I agree + My test method may not meet the requirements to the letter of the law but a quick rub will generate enough static to set it off if there is no other source around, I use the contact type on telecom not a physical safety issue but I also don’t want to damage the equipment so I use both. – Ed Beal Jun 14 at 18:02

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