Klein Tools RT390 Circuit Analyzer is a handheld circuit analyzer built for electricians, maintenance techs, inspectors, and serious DIY users who need more than a basic three-light outlet tester. This is a circuit analyzer designed for testing wiring faults, checking AFCI and GFCI devices, displaying line voltage, and measuring voltage drop on North American 120V AC 3-wire outlets. Model Number: RT390.

What separates this unit from a simple outlet checker is the screen and the depth of information it gives you. The large color LCD shows easy-to-understand results for common wiring faults, dual-open wiring faults, AFCI and GFCI status, voltage readings, and time-to-trip information. That matters when you are trying to diagnose a problem quickly without translating flashing lights or memorizing fault charts.

The RT390 also performs load testing at 12A, 15A, and 20A to measure percentage voltage drop. In practical terms, that means you can see how a circuit behaves under a meaningful load instead of only checking open-circuit voltage. For troubleshooting nuisance trips, weak branch circuits, and questionable outlet performance, that added data is what saves time.

Klein built this tester for actual field use. The housing uses ABS plastic with an overmold for better grip and added durability, and it is rated for 6.6 feet (2 m) drop protection. The detachable cord helps with storage, keeps the tester easier to pack, and gives you a little more flexibility when working around furniture, panels, or finished spaces.

Battery management is straightforward. The analyzer runs on three AAA alkaline batteries and powers off automatically after 5 minutes of inactivity to conserve battery life. That is a small feature, but if you carry a tester daily, it helps keep the tool ready instead of finding dead batteries when you need it.

From a safety standpoint, the unit is rated CAT III 135V and is intended for indoor use on North American 120V AC 3-wire electrical outlets. Consistent terminology matters here: this is not a general-purpose multimeter and it is not a non-contact tester. It is a specialty outlet and circuit analyzer made specifically for receptacle-based diagnostic work.

If your work involves service calls, residential troubleshooting, remodel punch work, facility maintenance, or verification of AFCI and GFCI protection, this tool makes sense. If all you need is a quick pass/fail outlet check, it may be more tester than you need. But if you want line voltage, fault identification, load-based voltage drop testing, and device trip data in one tool, the RT390 earns its spot in the bag.

Why the Klein Tools RT390 Circuit Analyzer earns a spot in the service bag

This is the kind of tester that makes sense for anyone who needs real outlet diagnostics, not just a quick yes-or-no check.

• Who it's for: Electricians, maintenance crews, inspectors, and serious troubleshooters working on 120V AC 3-wire receptacle circuits.
• Why it stands out: It combines clear LCD fault readouts, AFCI and GFCI testing, and load-based voltage drop measurement in one dedicated tool.
• Worth knowing: It is purpose-built for North American 120V AC outlets, so buy it for outlet diagnostics and branch-circuit testing, not as a replacement for a full multimeter.

• Does it test both AFCI and GFCI devices? Yes. The RT390 inspects AFCI and GFCI devices and provides trip time and trip current information.
• What outlets is it designed to work with? It is designed for North American 120V AC 3-wire electrical outlets.
• Can it measure voltage drop under load? Yes. It performs load testing at 12A, 15A, and 20A to measure percentage voltage drop.
• What kind of batteries does it use? It uses three AAA alkaline batteries and includes an automatic shutoff feature after 5 minutes of inactivity.