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Klein Tools · Klein Tools ET450 Advanced Circuit Breaker Finder and Wire Tracer Kit & RT390 Circuit Analyzer with Large LCD, Identifies Wiring Faults, GFCI and AFCI Tester, Voltage Drop, Displays Trip Time, Orange
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A bundle of two instruments. The ET450 is a circuit breaker finder and wire tracer stated to work on energized or non energized breakers, fuses and wires, detecting its transmitted signal through drywall, cement block and underground with adjustable sensitivity, able to trace wire, conduit, PVC pipe or one wire in a bundle, with audible and visual signal strength indication on the receiver. The RT390 is a circuit analyzer with a large colour display reporting wiring faults, AFCI and GFCI operation, voltage drop and device trip time. The tracer is described in four bullets and the analyzer in one, and the analyzer is the half whose value is entirely numeric.
Four bullets describe the tracer and one describes the analyzer
Look at how the bullets are labelled. Four of them begin with Product 1 and one begins with Product 2. That prefix is the tell: two separate product descriptions have been stapled together for a bundle listing, and nobody went back and merged the specifications.
The consequence is lopsided. The tracer gets its operating envelope, its penetration claim, its range of targets and its interface described. The analyzer gets a sentence that lists what appears on its screen.
That matters more than it would the other way round, because of what the two instruments produce. A tracer produces a position: this breaker, this wire in the bundle, this line under the floor. You verify it by switching the breaker and watching what goes dark, so the instrument proving itself is part of using it. An analyzer produces numbers, and a number you cannot verify by any other means has to come with a range, a resolution and an accuracy figure or it is just a reading on a screen.
None of those three appears for the analyzer anywhere on the page.
Energized or non energized is the line that decides a tracer
The first bullet is the strongest thing in the listing and it would be easy to skim.
A plug in breaker finder works by pushing a coded signal onto a live circuit from a transmitter in a socket, then sweeping the panel with a receiver until the coded tone peaks at one breaker. The mains current already flowing on the circuit is part of what makes that work, and the coding is what stops the receiver being fooled by the forty other things in the panel.
Tracing a circuit that has no voltage on it is a different problem. The transmitter has to drive its signal onto the conductor directly, the receiver has to find it with no load current helping, and the signal has to be strong enough to be found through plaster or a slab. An instrument that handles both cases needs to do both jobs, and the first bullet claims breakers, fuses and wires in either state.
That is the specification that separates this from the cheaper end of the category, where locators are often restricted to dead circuits or low voltage wiring and say so. Being able to work on a live installation without shutting it down is often the whole reason you reached for the tool. Our roundup of circuit breaker finders covers how the other instruments in this class handle it.
Two further claims in the second and third bullets are worth taking seriously: tracing a single wire within a bundle, and tracing conduit or PVC pipe. The first is the harder of the two, because every conductor in a bundle is coupled to the others and the tone leaks onto its neighbours, so narrowing from the bundle to the one wire is a matter of working by relative signal strength. The audible and visual strength indication in the fourth bullet is exactly the right interface for that, because the job is comparing one position against another rather than reading an absolute figure.
Trip time in milliseconds is what you are buying the RT390 for
The analyzer bullet lists wiring faults, AFCI, GFCI, voltage drops and device trip time. Of those, trip time is the one you cannot get any other way, and it deserves explaining.
A ground fault device compares outgoing and returning current and opens when they differ by more than a few milliamps, because that difference means current is leaving the circuit by some other path. An arc fault device does something quite different: it watches the current waveform for the irregular, chaotic signature of an arcing connection, which is a fire hazard rather than a shock hazard. They are separate protections against separate dangers, a receptacle may carry one, both or neither, and each has to be tested on its own terms.
Testing them means forcing a trip. But whether the device trips is only half the answer, because protection is a race against the thing it protects against. A device that opens sluggishly has partially failed while still appearing to work, and the only way to catch that is to measure the interval between the fault being applied and the contacts opening.
So the trip time readout is the product. And the listing gives no range for it, no resolution, no accuracy, and no statement of the fault current used to force the trip, which is the condition the time is measured under. Our comparison of receptacle testers shows how often those figures are published.
Voltage drop finds what a three lamp tester calls fine
The other measurement in that bullet is the one that changes what you can find on a service call.
A basic receptacle tester lights a pattern of neon lamps and tells you the line, neutral and ground conductors are in the right terminals. It draws almost no current to do it, and that is the limitation. A push in connection that has loosened, a splice that has corroded, a run that is too long or a conductor that is undersized for its load will all produce a perfect three lamp pattern, because none of those faults does anything until current flows.
A voltage drop test applies a load and measures how far the terminal voltage falls. The voltage lost in the wiring is the current multiplied by the resistance of the path, so a drop that is larger than it should be is a direct report of resistance you cannot see. It is the difference between confirming that the wiring is connected correctly and confirming that it is sound.
What the listing does not say is the test current. A drop figure means nothing without it, because the same resistance gives a small drop at a light load and an alarming one at a heavy load. That is one more number the single bullet leaves out. Our overview of electrical testers covers the instruments that publish it.
Through drywall, cement block and underground, with no depth figure
| Specification | Published in the listing |
|---|---|
| Tracer circuit state | Energized or non energized breakers, fuses and wires |
| Tracer penetration claim | Drywall, cement block, underground |
| Tracer sensitivity | Adjustable levels |
| Tracer targets | Wire, conduit, PVC pipe, a single wire in a bundle |
| Tracer indication | Audible and visual signal strength on the receiver |
| Analyzer display | Large colour screen |
| Analyzer readings | Wiring faults, AFCI, GFCI, voltage drop, device trip time |
| Tracer maximum depth | Not stated in the listing bullets |
| Tracer tone frequency | Not stated in the listing bullets |
| Transmitter output | Not stated in the listing bullets |
| Analyzer voltage range | Not stated in the listing bullets |
| Trip time range and resolution | Not stated in the listing bullets |
| Test current for the voltage drop measurement | Not stated in the listing bullets |
| Accuracy, any reading | Not stated in the listing bullets |
| Measurement category rating, either instrument | Not stated in the listing bullets |
| Battery type and life | Not stated in the listing bullets |
The underground claim is the one to press on. Detecting a transmitted signal underground is a real capability and the adjustable sensitivity suggests it is meant seriously, but a locator that claims underground detection without a maximum depth is making a weaker statement than instruments a fraction of its outlay, which publish a depth figure even when that figure is modest. Depth is the first question anyone asks of an underground trace.
The absent measurement category rating is the other row worth noting, because the analyzer plugs into a live receptacle and forces faults on protective devices. That is work on an energized installation, and a rating is how an instrument documents what it can survive while doing it.
Right for a service van, with one question to settle first
As a working pair these two instruments cover complementary ground, and the combination is a sensible one. The tracer answers where, on live or dead circuits, through finishes and underground. The analyzer answers whether, on the protective devices and the soundness of the wiring behind the socket. Between them they handle most of a day of residential or light commercial fault finding without reaching for anything else, and the arc fault, ground fault, trip time and voltage drop set is the right list of things to be able to check at a receptacle.
The reservation is entirely about documentation rather than the hardware. If you are using a trip time to condemn a protective device or a voltage drop to justify rewiring a run, you want the range, the resolution, the test current and the accuracy behind those figures, and this page does not give you any of them. Get the analyzer specification sheet before relying on its numbers in front of a customer.
Skip the bundle if you only need one half. A tracer alone is the right purchase for someone chasing circuits in a panel, and an analyzer alone is the right purchase for someone commissioning receptacles. Paying for both only makes sense if both are in your week.
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Products shown because their documented specifications fit this guide. Price and availability are on Amazon and can change.
Frequently Asked Questions
What is the difference between AFCI and GFCI, and why test both?
They protect against different things. A ground fault device compares the current flowing out on the line with the current returning on the neutral, and opens when the difference exceeds a few milliamps, because that difference means current is finding another path, possibly through a person. An arc fault device watches the shape of the current waveform for the erratic signature of an arcing connection, which is a fire risk rather than a shock risk. A receptacle can carry either, both, or neither, and the two have to be tested separately because a device that passes one test tells you nothing about the other.
Why does trip time matter if the device trips at all?
Because protection is a race. The point of a ground fault device is to interrupt the current before the shock does lasting harm, and the point of an arc fault device is to interrupt before the arc starts a fire. A device that opens eventually has partially failed, and the only way to know is to force a trip and measure how long it took. That is the number the analyzer exists to produce, and it is also the number this listing publishes no resolution or accuracy for.
What does a voltage drop test show that an outlet tester does not?
Resistance that only reveals itself under load. A three lamp receptacle tester draws almost nothing, so it confirms the conductors are in the right terminals and nothing else. A loose push in connection, a corroded splice, an overlong run or an undersized conductor all look perfect to it. Apply a load and measure how far the voltage falls and that hidden resistance appears as a drop, because the voltage lost in the wiring is the current multiplied by the resistance in the path. It is the difference between checking the wiring is right and checking it is sound.
Can the ET450 trace a dead circuit?
Yes, and the listing says so in its first bullet, which is the single most important line about it. Tracing a circuit with no voltage on it means the transmitter has to drive a signal onto the conductor itself rather than riding on the mains, and the receiver has to find that signal without any load current helping it along. Supporting both energized and non energized work is what makes this a kit rather than a plug in breaker finder, and it covers the cases a low voltage only locator cannot.
What is missing from the analyzer side of this listing?
Almost everything measurable. There is no voltage range, no trip time range or resolution, no statement of the test current used for the voltage drop measurement, no accuracy figure and no measurement category rating. For an instrument whose output is numbers that is a serious gap, and the explanation is visible in the bullet prefixes: the two product descriptions were stapled together and nobody merged the specifications.
What is missing on the tracer side?
The tone frequency, the transmitter output and any depth figure. The second bullet claims detection through drywall, cement block and underground, and underground detection with no depth number is a weaker claim than much cheaper locators make, because they at least publish a maximum depth. Battery type and life are also absent for both instruments.
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