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Klein Tools RT390 Circuit Analyzer with Large LCD, Identifies Wiring Faults, GFCI and AFCI Tester, Voltage Drop, Displays Trip Time

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Brand	Klein Tools
Power source	Battery Powered
Style	Receptacle Tester w/Voltage Drop
Colour	Orange
Item weight	0.49 Pounds
Item dimensions L x W x H	18 x 6.9 x 3.8 Centimetres
Min. Operating voltage	135 Volts (AC)
Specification met	Cat Iii 135v, Afci, Gfci, Ul, Fcc
Upper temperature rating	55 Degrees Celsius
Measurement type	Voltmeter, Ammeter, Ohmmeter, Time-based

About this item

CLEAR COLOR LCD DISPLAY: Circuit Analyzer with large color LCD provides easy-to-understand results for wiring faults, AFCI, GFCI, voltage drops, and device trip time
COMPREHENSIVE WIRING FAULT DETECTION: Detect and identify common wiring faults in standard, AFCI, and GFCI electrical outlets, ensuring thorough evaluation
DUAL WIRING FAULT DETECTION: Capable of detecting dual wiring faults, including open neutral and open ground, enhancing safety measures
AFCI AND GFCI DEVICE INSPECTION: Inspect AFCI and GFCI devices, measuring trip time and trip current for accurate functionality assessment
LOAD TESTING CAPABILITIES: Conduct 12A, 15A, and 20A load testing to measure percentage voltage drops, providing valuable insights into electrical performance

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Product details

Product Dimensions ‏ : ‎ 17.96 x 6.91 x 3.84 cm; 222.26 g
Date First Available ‏ : ‎ April 21 2023
Manufacturer ‏ : ‎ Klein Tools
ASIN ‏ : ‎ B0BT87LJRL
Item model number ‏ : ‎ RT390
Department ‏ : ‎ Unisex-Adult
�鶹�� Rank: #299,633 in Tools & Home Improvement (See Top 100 in Tools & Home Improvement)
- #467 in Circuit Testers
Customer Reviews:
164 ratings

This item: Klein Tools RT390 Circuit Analyzer with Large LCD, Identifies Wiring Faults, GFCI and AFCI Tester, Voltage Drop, Displays Trip Time

$233.63

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Product description

The Klein Tools RT390 is a Circuit Analyzer that tests the wiring conditions at an electrical outlet, displays AC line voltage, inspects AFCI and GFCI devices with time to trip device, and performs voltage drop tests at 12A, 15A and 20A current loads. Results are easy to understand with large, color LCD. The tester is designed for use with North American 120V AC 3-wire electrical outlets. For more than 160 years, Klein Tools has manufactured premium-quality, professional-grade hand tools that deliver the performance, durability and precision needed to get the job done right. Our family of engineers, workers and craftsman continue to put six generations of expertise into every tool we create by using only the highest quality materials, superior workmanship, and keeping manufacturing as close to home as we can. Klein isn't just the name of our company, it's also our family name. And since we're an American company that's family-owned and family-run, you know you can count on us to be here tomorrow. Klein Tools doesn't just make great products, we make great products that stand up to the demands of the professionals who use them every day ... Since 1857.

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About Klein Tools

As an American manufacturer of hand tools for more than 160 years, Klein Tools makes premium-quality, professional-grade tools that deliver performance, durability and precision. Our team continues to put six generations of expertise into each tool by using the highest quality materials and superior workmanship.

Klein Tools doesn't just make great products, we make great products that stand up to the demands of the professionals who use them every day … Since 1857.

Circuit Analyzer with Large LCD, Identifies Wiring Faults, GFCI and AFCI Tester, Voltage Drop, Displays Trip Time

Circuit Analyzer with large color LCD displays easy to understand results for wiring faults, AFCI, GFCI, voltage drops and time to trip devices
Detect and identify common wiring faults in standard, AFCI and GFCI electrical outlets
Detects dual (open neutral/open ground) wiring faults
Inspect AFCI and GFCI devices; includes trip time and trip current
12A, 15A, and 20A load testing to measure percentage voltage drops
Powers off automatically after 5 minutes of inactivity to conserve battery life
Detachable cord for easy storage
For use with North American 120V AC 3-wire electrical outlets

FEATURES

Circuit Analyzer identifies common GFCI and AFCI wiring faults

Large color LCD shows trip time and trip current

Displays AC voltage and voltage drop percentages

	AFCI /GFCI Outlet Tester	GFCI Receptacle Tester with LCD	Advanced Circuit Tracer Kit	Digital Circuit Breaker Finder with GFCI Outlet Tester	Dual Range NCVT with Receptacle Tester Electrical Test Kit	Dual Range NCVT and AC/DC Voltage Tester Electrical Test Kit
	Buying Options	Buying Options		Buying Options	Buying Options
Customer Reviews	13,611	10,037	1,183	22,197	3,479	1,073
Mfg. No.	RT310	RT250	ET450	ET310	NCVT2PKIT	NCVT3PKIT
Description	AFCI /GFCI Outlet Tester	GFCI Receptacle Tester with LCD	Advanced Circuit Tracer Kit	Digital Circuit Breaker Finder with GFCI Outlet Tester	Dual Range NCVT with Receptacle Tester Electrical Test Kit	Dual Range NCVT and AC/DC Voltage Tester Electrical Test Kit

	Premium Dual-Range NCVT and GFCI Receptacle Tester Electrical Test Kit	AC/DC Voltage and GFCI Receptacle Outlet Test Kit	Digital Multimeter, Manual-Ranging, 600V	Digital Multimeter, TRMS Auto-Ranging, 600V, Temp	Slim Digital Multimeter, TRMS Auto-Ranging, 600V, Temp	Digital Multimeter, TRMS Auto-Ranging, 1000V, Temp, Low Impedance
			Buying Options	Buying Options	Buying Options
Customer Reviews	1,621	301	1,799	308	207	206
Mfg. No.	RT250KIT	ET45VP	MM325	MM420	MM450	MM720
Description	Premium Dual-Range NCVT and GFCI Receptacle Tester Electrical Test Kit	AC/DC Voltage and GFCI Receptacle Outlet Test Kit	Digital Multimeter, Manual-Ranging, 600V	Digital Multimeter, TRMS Auto-Ranging, 600V, Temp	Slim Digital Multimeter, TRMS Auto-Ranging, 600V, Temp	Digital Multimeter, TRMS Auto-Ranging, 1000V, Temp, Low Impedance

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Customer reviews

164 global ratings

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Leigh Hardy
A unique tool. Expensive
Reviewed in Canada on December 30, 2024
Verified Purchase

Works well. Expensive for what it does.
If I ever need to replace it.... I would look for a cheaper option.

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One person found this helpful

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�鶹�� Customer
Great product
Reviewed in Canada on March 31, 2024
Verified Purchase
Love the fact it does voltage drop test

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One person found this helpful

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Scott McClelland
Very Nice Tool
Reviewed in Canada on October 4, 2024
Verified Purchase
Easy to use and works very well. As an electrical contractor, I find this tool invaluable for assessing GFCI & AFCI function. The circuit load test feature is also a very convenient and valuable tool.
Quite a good price for the work that it is capable of accomplishing, in my opinion. Next level of development could be the ability to log and archive test results.

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2 people found this helpful

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Eduardo Javier Renteria
Muy bueno pero las baterías que trae son basura
Reviewed in Mexico on August 4, 2024
Verified Purchase

Lo único vamos del producto es que las baterías se dañan muy rápido, hablo que una semana después de ponerlas se vaciaron :( así que recomiendo quitarlas cada que no lo usen o ponerle desde el principio unas de buena calidad

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CPSS
Easy to see problems
Reviewed in the United States on June 1, 2025
Verified Purchase
Works great, just what I need for troubleshooting

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Nutmegger
Really good, could have been perfect
Reviewed in the United States on May 5, 2024
Verified Purchase
The good: It is the only tester available in the US at the time of my writing this that can test every AFCI receptacle and breaker. Some testers on Youtube reported that it fails to trip the "purple" Homeline dual-function GFCI/AFCI breakers on shorter cable runs (really puzzing there), but I didn't encounter that.
Tests everything reliably, including voltage drop.
A couple of irritations:
The female end of the "pigtail" plug tends to slide out of the device, sometimes ever so slightly, looking like it's plugged in, but it's not. This can create a dangerous sense of security making you think that receptacle is not powered. Also, it has a "hold" function that keeps showing the voltage for about 10 seconds after the receptacle lost power or the device was unplugged from the receptacle. It can be useful, but there should be a way to turn it off. I couldn't find how.

Read more
Jeff C.
Great for checking receptacles for more than just correct wiring
Reviewed in the United States on June 2, 2025
Verified Purchase
I got the Klein RT390 mainly to look at voltage drop; I have one GFCI outlet and no GFCI or AFCI breakers. Given that, I probably didn’t stress the analyzer as much as some of the other reviewers did. I’m also not a practicing electrician, so I haven’t given the unit heavy use. My rating is based on using it only a few times, and it’s something I probably won’t be repeating on a daily basis—so I cannot really comment on reliability.

The RT390 greatly simplifies measuring voltage drop by giving results at three different loads—12 A, 15 A, and 20 A—with the press of a button. The results are displayed for five minutes, even if the cable is disconnected, so it’s easy to take the analyzer to a computer to record the results; I put them into a spreadsheet that does some additional calculations, like estimating the length of the circuit under test.

Detachable Cable
The detachable cable is handy; anything with an IEC C13 connector can also be used. The 1’ cable supplied can be a bit short for some applications; I got 2′ and 3′ 14 AWG cables for some harder-to-reach locations; you probably could go a bit longer without serious problems. I also got a NEMA 5-15P to IEC C13 adapter (https://www.amazon.com/dp/B0CT7HB42J) for direct plug in and an Ideal 61-183 SureTest® alligator clip adapter (https://www.amazon.com/dp/B000R99RFI) for connections other than receptacles.

A Sturdier Case
It’s nice that Klein provide a case, but unlike most Fluke cases, the case isn’t padded and isn’t very protective—I would not want to drop it. The RT390 costs as much as many multimeters, so it’s worth protecting. To address this, I got a Jinmei EVA hard case (https://www.amazon.com/dp/B0C24N9Z5W).

Testing Ungrounded Devices
As has been noted by some others, the analyzer will not perform any tests with “incorrect” wiring, so out of the box, it cannot be used on ungrounded receptacles or lamp sockets. But it’s simple to work around this if a good ground is available. I have a grounding wire that plugs into a grounded receptacle. I’ve used it to properly ground an antistatic mat; many of the better antistatic mats include such an adapter. I made mine from an old extension cord, but it could easily be made with green wire and a plug. I only extended the grounding conductor. I retained the neutral blade on the plug to keep the plug from spinning in the receptacle; I cut off the line blade and taped over it to minimize any chance of something unpleasant happening. If you make an adapter from scratch, connect only a green wire, and there should be no problem

Finding the Source of a Voltage Drop
As supplied, the RT390 is mainly intended for testing receptacles. If a test result shows an unacceptable voltage drop, the logical approach is to test points closer and closer to the supply. But if the available test points nearest the supply are light fixtures, switches, or junction boxes, plugging into a receptacle isn’t an option.

Testing a Light Fixture
The analyzer cable is inserted into a 3-wire to 2-wire plug adapter inserted into a socket adapter, and the grounding wire is connected to the grounding tab on the plug adapter. It’s a bit trickier if there aren’t any grounded receptacles handy, but a grounding wire can be connected to some other reasonable ground is available. I didn’t need to do this, so I can’t comment on what constitutes a “reasonable” ground.

Do be aware that while a socket adapter (https://www.amazon.com/dp/B0CDRFPD9G) accepts a 3-wire plug, it does not provide a protective ground because there is no ground in the socket to which it can connect.

A Problem I’d Never Have Thought to Investigate
Doing a test on a light fixture above a kitchen sink was revelatory. With my grounding hack connected, the RT390 happily … refused to do the test because the line and neutral were reversed. A check with a DMM confirmed that the socket threads were energized—and apparently have been for 70 years (I guess this stuff wasn’t taken too seriously in the era of 2-wire nonpolarized plugs). Arguably not the world’s worst safety hazard, but if one were to screw in a bulb with the socket energized and manage to touch the threads, it might not be fun. Especially if water had been splashed on the floor. After the fixture was correctly wired, the analyzer was glad to complete the test. I’d probably never have thought to test the fixture for correct wiring, though I’d have preferred the analyzer to apprise me of the reversed line and neutral at the same time it complained of the open ground.

Testing a Switch or Other Connection Point
If the neutral is accessible, connection can be made to switch terminals or splices, but it requires some improvised wiring. For a switch, you may need to disconnect the line from the switch terminal; for a splice, you’ll probably need to remove the wire nut (or the insulator or tape from a crimped ferrule). Connection to the RT390 can be made with something like the Ideal SureTest® alligator clip adapter. When connecting something like this to a switch or to light-fixture wiring, it’s imperative to take the utmost care to avoid a short circuit or even connections so close as to allow arcing.

It’s possible to make an alligator-clip adapter; an internet search should find some examples. If doing so, you should be very careful, especially with alligator clips that aren’t fully insulated like those on the SureTest® adapter. It’s a risk I wasn’t willing to risk.

A Low-Cost Alternative
You can do a surprisingly good job with an inexpensive power meter (such as a P3 Kill A Watt; I have the P4400) and something like a hair dryer, but it can be a bit tedious, and there’s limited choice of loads. Unlike a Kill A Watt, though, the RT390 doesn’t show the actual current; I’m not sure the nominal loads are adjusted for voltage drop. I’m not sure it really matters, though. Results with the RT390 track pretty closely with those with the Kill A Watt and hair dryer. Since the hair dryer is a real load, this suggests that the RT390 is performing a good test.

Conclusion
There are other testers—like the Extech CT270 (https://www.amazon.com/dp/B0058ELNFY)—that provide more information for a lot more money. And there are others that cost far more than that; some—like models from Ideal and Amprobe—appear to have been discontinued. For someone who’s not an electrician, even the RT390 is arguably massive overkill. Many simple testers will check for correct receptacle wiring; every home should have one. But it is nice to know if you have excessive voltage drop, especially in an older building. And especially if you strongly suspect that you have some marginal wiring. The RT390 makes that testing a breeze.

Read more

Jeff C.

Great for checking receptacles for more than just correct wiring

Reviewed in the United States on June 2, 2025
I got the Klein RT390 mainly to look at voltage drop; I have one GFCI outlet and no GFCI or AFCI breakers. Given that, I probably didn’t stress the analyzer as much as some of the other reviewers did. I’m also not a practicing electrician, so I haven’t given the unit heavy use. My rating is based on using it only a few times, and it’s something I probably won’t be repeating on a daily basis—so I cannot really comment on reliability.

The RT390 greatly simplifies measuring voltage drop by giving results at three different loads—12 A, 15 A, and 20 A—with the press of a button. The results are displayed for five minutes, even if the cable is disconnected, so it’s easy to take the analyzer to a computer to record the results; I put them into a spreadsheet that does some additional calculations, like estimating the length of the circuit under test.

Detachable Cable
The detachable cable is handy; anything with an IEC C13 connector can also be used. The 1’ cable supplied can be a bit short for some applications; I got 2′ and 3′ 14 AWG cables for some harder-to-reach locations; you probably could go a bit longer without serious problems. I also got a NEMA 5-15P to IEC C13 adapter (https://www.amazon.com/dp/B0CT7HB42J) for direct plug in and an Ideal 61-183 SureTest® alligator clip adapter (https://www.amazon.com/dp/B000R99RFI) for connections other than receptacles.

A Sturdier Case
It’s nice that Klein provide a case, but unlike most Fluke cases, the case isn’t padded and isn’t very protective—I would not want to drop it. The RT390 costs as much as many multimeters, so it’s worth protecting. To address this, I got a Jinmei EVA hard case (https://www.amazon.com/dp/B0C24N9Z5W).

Testing Ungrounded Devices
As has been noted by some others, the analyzer will not perform any tests with “incorrect” wiring, so out of the box, it cannot be used on ungrounded receptacles or lamp sockets. But it’s simple to work around this if a good ground is available. I have a grounding wire that plugs into a grounded receptacle. I’ve used it to properly ground an antistatic mat; many of the better antistatic mats include such an adapter. I made mine from an old extension cord, but it could easily be made with green wire and a plug. I only extended the grounding conductor. I retained the neutral blade on the plug to keep the plug from spinning in the receptacle; I cut off the line blade and taped over it to minimize any chance of something unpleasant happening. If you make an adapter from scratch, connect only a green wire, and there should be no problem

Finding the Source of a Voltage Drop
As supplied, the RT390 is mainly intended for testing receptacles. If a test result shows an unacceptable voltage drop, the logical approach is to test points closer and closer to the supply. But if the available test points nearest the supply are light fixtures, switches, or junction boxes, plugging into a receptacle isn’t an option.

Testing a Light Fixture
The analyzer cable is inserted into a 3-wire to 2-wire plug adapter inserted into a socket adapter, and the grounding wire is connected to the grounding tab on the plug adapter. It’s a bit trickier if there aren’t any grounded receptacles handy, but a grounding wire can be connected to some other reasonable ground is available. I didn’t need to do this, so I can’t comment on what constitutes a “reasonable” ground.

Do be aware that while a socket adapter (https://www.amazon.com/dp/B0CDRFPD9G) accepts a 3-wire plug, it does not provide a protective ground because there is no ground in the socket to which it can connect.

A Problem I’d Never Have Thought to Investigate
Doing a test on a light fixture above a kitchen sink was revelatory. With my grounding hack connected, the RT390 happily … refused to do the test because the line and neutral were reversed. A check with a DMM confirmed that the socket threads were energized—and apparently have been for 70 years (I guess this stuff wasn’t taken too seriously in the era of 2-wire nonpolarized plugs). Arguably not the world’s worst safety hazard, but if one were to screw in a bulb with the socket energized and manage to touch the threads, it might not be fun. Especially if water had been splashed on the floor. After the fixture was correctly wired, the analyzer was glad to complete the test. I’d probably never have thought to test the fixture for correct wiring, though I’d have preferred the analyzer to apprise me of the reversed line and neutral at the same time it complained of the open ground.

Testing a Switch or Other Connection Point
If the neutral is accessible, connection can be made to switch terminals or splices, but it requires some improvised wiring. For a switch, you may need to disconnect the line from the switch terminal; for a splice, you’ll probably need to remove the wire nut (or the insulator or tape from a crimped ferrule). Connection to the RT390 can be made with something like the Ideal SureTest® alligator clip adapter. When connecting something like this to a switch or to light-fixture wiring, it’s imperative to take the utmost care to avoid a short circuit or even connections so close as to allow arcing.

It’s possible to make an alligator-clip adapter; an internet search should find some examples. If doing so, you should be very careful, especially with alligator clips that aren’t fully insulated like those on the SureTest® adapter. It’s a risk I wasn’t willing to risk.

A Low-Cost Alternative
You can do a surprisingly good job with an inexpensive power meter (such as a P3 Kill A Watt; I have the P4400) and something like a hair dryer, but it can be a bit tedious, and there’s limited choice of loads. Unlike a Kill A Watt, though, the RT390 doesn’t show the actual current; I’m not sure the nominal loads are adjusted for voltage drop. I’m not sure it really matters, though. Results with the RT390 track pretty closely with those with the Kill A Watt and hair dryer. Since the hair dryer is a real load, this suggests that the RT390 is performing a good test.

Conclusion
There are other testers—like the Extech CT270 (https://www.amazon.com/dp/B0058ELNFY)—that provide more information for a lot more money. And there are others that cost far more than that; some—like models from Ideal and Amprobe—appear to have been discontinued. For someone who’s not an electrician, even the RT390 is arguably massive overkill. Many simple testers will check for correct receptacle wiring; every home should have one. But it is nice to know if you have excessive voltage drop, especially in an older building. And especially if you strongly suspect that you have some marginal wiring. The RT390 makes that testing a breeze.

Images in this review

Snickerdoodle
Won’t test non grounded outlets WITHOUT my setup.
Reviewed in the United States on March 15, 2025
Verified Purchase
Bought this to do load testing on old non grounded outlets. Won’t work by itself. I made a male to make ground plug(see picture). Just need a grounded outlet somewhere, use extension cord and plug into bottom side of same outlet. Worked fine, can also use this setup to test gfci and afci. The adapter should only extend the ground lead so as NOT to be a suicide cord. Test the grounded outlet first to verify its wire correctly ( not hot ground reverse ). This is just a temporary setup to supply the ground that the tester is looking for BEFORE running its test. I am not an electrician. If uncertain or not familiar with electricity leave it alone.

Read more

Snickerdoodle

Won’t test non grounded outlets WITHOUT my setup.

Reviewed in the United States on March 15, 2025
Bought this to do load testing on old non grounded outlets. Won’t work by itself. I made a male to make ground plug(see picture). Just need a grounded outlet somewhere, use extension cord and plug into bottom side of same outlet. Worked fine, can also use this setup to test gfci and afci. The adapter should only extend the ground lead so as NOT to be a suicide cord. Test the grounded outlet first to verify its wire correctly ( not hot ground reverse ). This is just a temporary setup to supply the ground that the tester is looking for BEFORE running its test. I am not an electrician. If uncertain or not familiar with electricity leave it alone.

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