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

One has the option of a number of GFCI testers of which the Klein RT 310 and 350, the Fluke Pro 120+ are generally the best. But there's a new king in town. The RT390 is expensive and bulky, but it absolutely demands to be in the kit of any home inspector, safety inspector, electrician, or any homeowner who plans to do more than incidental work on their electrical systems. First, the arrival of AFCI's and especially hybrid AFCI/GFCI's has changed the outlet tester game. These breakers, Arc Fault Circuit Interruptors, detect arcs in the wiring and are most effective in identifying and protecting against electrical fires (GFCI's protect more directly against shocks emanating from the outlet and attached products). Most outlet testers don't test AFCI's. The Klein RT250 is a basic GFCI tester. Bump up to a RT310 and you get AFCI testing as well, but there's no diagnostic capability in the 310 -- it's a simple go/no-go tester that can't tell you anything about what's wrong. The RT350 does a bit more, but doesn't generate enough data for you to figure out what's wrong or how to fix it. I wouldn't generally recommend the 350 now that the 390 is available. The RT390 offers a number of significant advantages: First, it tests any outlet for both arc and ground fault integrity. Second, it tests at multiple trip levels so you can predict whether you just have a tired or non-exercised interruptor. Testing it side by side with a 350, the 390 was notably more consistent and accurate than the 350, in particular with regards to false negatives (the 390 identified arc faults in four times more installations than the 350. And lastly, the 390 is much more rugged in the case design, the cable connector, and the sturdiness of the internal circuit boards and components. What is missing in the 390? I'd love to see a set of clip leads so I could test an outlet box at the bare wires before installing the receptacle, And at nearly $200 a hard foam case would be appreciated. However, these are nits. This can be the most significant risk-prevention tool in your toolbox and should replace non-contact sniffers and the cheaper GFCI testers that we all carry around and rely on. Five stars from me.

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 take. Testing Extension Cords A less obvious application is testing extension cords. On a whim, I checked a few and found that not all are created equal. In most cases, the drop is greater than would be predicted from the length and the wire size but not really a big deal. With several cords, however—interestingly, all from the same manufacturer—the voltage drop was astonishing. Suffice it to say those cords are unsuitable for all but the lightest loads. The procedure is simple: first, take a measurement with the RT390’s power cord connected to the receptacle; next, repeat the test with the extension cord between the receptacle and the power cord. Then subtract the voltage drop in the first test from that of the second to get the voltage drop of the extension cord. Results vary slightly from test to test, so it’s probably a good idea to do the tests several times and use the average results. When testing several extension cords, I usually repeat the test using the RT390’s power cord alone and use the average of these tests. 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.

Great circuit analyzer. Very easy to use and accurate. This analyzer will save your house from a fire. Due to the load info.

Next level diagnostics, with a ten second quantitative voltage drop test to verify circuit integrity.

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.

Working well and looks like the information it provides can be trusted.

A must have for the diy’er and good enough for the professional and really easy to use.

Does not replace a multy meter but is a Very good analyzer. Heavy duty made.

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

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

Love the fact it does voltage drop test