Klein Rt 250

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The Klein RT250 is a plug-in GFCI receptacle tester with a backlit LCD. It checks a three-wire, 120-volt North American outlet for common wiring faults and shows how long a GFCI device takes to trip. If you searched for “klein rt 250”, you probably want to know how to run the test, what the display tells you, and what the tester cannot confirm. This guide explains those points using Klein’s product page, a distributor listing and an independent review.

Quick answer

• The RT250 plugs into a 3-wire, 120-volt North American receptacle and shows wiring conditions on a backlit LCD.
• It shows the trip time of a GFCI device, which Klein lists as a standard function.
• Klein rates it CAT II 135V and lists it for use on 3-wire North American 120-volt outlets only.
• It runs on two AAA batteries, which Klein includes, and it has an auto-hold feature.

What the RT250 checks

Klein’s product page says the RT250 identifies common wiring faults. It also describes a patent-pending open neutral and open ground detection feature. The LCD shows the voltage at the outlet, and the tester uses green and red LED indicators to show conditions. In the review we opened, green is treated as normal and red as a problem to investigate. That is a useful habit: a single glance tells you whether to keep going or stop and look closer.

The tester is aimed at standard household receptacles. Klein lists the product as GFCI-capable and as not AFCI, so it does not test arc-fault breakers. If you need to check an AFCI function, you need a different tool or a qualified technician. The RT250 is a receptacle tester, not a whole-panel diagnostic.

Running the GFCI trip-time test

The trip-time feature is the main reason people buy this model. Klein’s listing says the LCD shows the time required to trip a GFCI device. The distributor listing and the review repeat the same function. The sources describe the reading as the time the GFCI takes to trip during the check, which is what you use to confirm the protection responds.

Because a GFCI test interrupts power, plan the check. Tell anyone using the connected equipment that the outlet will cut out. Keep the test to the device you intend to check. Do not repeat the trip test many times in a row on one device, because that is not a recommended way to age-test a GFCI.

Reading the wiring results

After you plug in, the tester displays the voltage and any wiring condition it finds. Klein’s listing names common faults such as open ground, open neutral and reversed polarity. The review we opened describes the same kinds of conditions. When the tester flags a fault, the right step is to stop and have the wiring checked by a qualified electrician. The tester identifies a condition. It does not repair it.

The auto-hold feature keeps the reading on screen after you pull the tester from a hard-to-reach outlet. That is useful when the outlet sits behind furniture or low on a wall. Klein lists auto-hold as one of the tester’s features, and the review we opened calls it helpful for outlets that are hard to see.

Where the tester fits in a check

A receptacle tester is most useful as the first step in a short checklist. Plug it in, read the voltage and the wiring condition, and then decide whether the outlet needs a closer look. If the outlet looks fine, the tester gives you a quick confidence check that the power and grounding are where they should be. If it flags a condition, you have a clear reason to call in an electrician instead of guessing. The RT250 does not replace a GFCI test button on the device itself, and it does not replace a full inspection of a home’s wiring. It gives you a fast, repeatable answer for a single outlet.

Ratings, batteries and limits

Klein’s specifications list a rated voltage of 135 volts AC and a safety rating of CAT II 135V. The product page says it is for use on 3-wire North American 120-volt receptacles only. Do not use it on 240-volt outlets, on non-North American outlets or on any circuit outside its stated use. The CAT II rating describes the environment the tool is built for. It does not make work on live wiring safe, and you should not open a receptacle to test its terminals unless you are trained to do so.

The RT250 takes two AAA batteries, and Klein includes them. The product page lists the drop protection as 2 meters, or 6.6 feet. The dimensions are 4.5 inches long, 2 inches wide and 1.1 inches high, and the weight is 4.8 ounces, or 136 grams.

What the sources do not cover

The Klein page and the distributor listing do not state an accuracy figure for the voltage display. They also do not state an accuracy figure for the trip-time reading. We could not confirm how closely the reading matches a reference instrument. Treat the trip time as a field check of whether a GFCI responds, not as a calibrated measurement.

The Klein page and the distributor listing do not describe an audible alarm, so the result depends on the LCD and LEDs. If you work in a noisy place, make sure you can see the display before you act on a result.

How we chose

This article covers only the Klein RT250. We began with Klein’s product page, because the manufacturer’s listing gives the test functions, the rating and the batteries most directly. We then opened a distributor listing that repeats those specifications, and an independent review for the usage notes. We did not use marketplace star ratings, because this article is about how to run the test and read the results.

What we could not verify

• The sources we opened do not give an accuracy figure for the voltage or trip-time display.
• The open neutral and open ground detection is described by Klein as patent-pending. We did not find independent testing of that claim.
• The sources do not say how the tester performs on a GFCI with a non-standard trip curve.
• The pages do not say whether the RT250 is discontinued. The Klein page shows no discontinued notice.
• The review we opened does not list durability data, and we did not find reliability figures for this model.

FAQ

What does the klein rt 250 test?

It checks a 3-wire North American 120-volt receptacle for common wiring faults, shows the voltage on an LCD and displays the trip time of a GFCI device.

Can it test AFCI breakers?

No. Klein lists the RT250 as GFCI but not AFCI.

Does the RT250 work on 240-volt outlets?

No. Klein lists it for 3-wire, North American 120-volt receptacles only.

What power does it use?

Two AAA batteries. Klein includes them with the tester.

What does the green and red light mean?

The review we opened reads green as normal and red as a problem condition. Use the LCD text to confirm which fault the tester has found.

Does the tester fix a wiring fault?

No. It identifies a condition, and a qualified electrician should investigate and correct it.

Bottom line

The Klein RT250 is a practical GFCI receptacle tester for 120-volt North American outlets. Use it for the wiring check and the trip-time reading, read the LCD before you act, and bring in a qualified electrician for any fault it flags. It does not replace a full electrical inspection.

Related reading on this site: outlet and GFCI testers compared and how to check a GFCI outlet.

Sources

• Klein Tools, GFCI Receptacle Tester with LCD, RT250: https://www.kleintools.com/product/RT250 (opened 2026-10-29)
• Global Test Supply, Klein Tools RT250 GFCI Receptacle Tester with LCD: https://www.globaltestsupply.com/product/klein-tools-rt250-gfci-receptacle-tester-with-lcd (opened 2026-10-29)
• AtoZ Reviews, Klein Tools RT250 GFCI Outlet Tester Review: https://atozreviews.com/2025/05/19/klein-tools-rt250-gfci-outlet-tester-review/ (opened 2026-10-29)