COMPARISON · MULTIMETERS
Fluke 117 vs Extech EX355: Which Is Better for Field Technicians?
These two are closer than the price suggests: both are CAT III 600V True RMS meters with a low-impedance input and a built-in non-contact detector. The Fluke 117 cost about twice the EX355 on Amazon when we checked. Field techs who service drives, rooftop units and furnaces should buy the EX355, which adds a low-pass filter, microamp ranges and a thermocouple input. Electricians who mostly prove circuits dead should buy the 117 for its AC/DC AutoVolt input, wider specified AC bandwidth and the simplest workflow.
By the OhmSavvy Research Team ·
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Fluke 117
4.8★★★★★The meter working electricians actually buy with their own money, not just the one brands push.
Extech EX355
4.4★★★★☆A compact True RMS meter with LoZ, a low-pass filter, NCV, µA ranges and temperature, rated CAT III 600V.
Specs side by side
| Fluke 117 | Extech EX355 | |
|---|---|---|
| Rating | 4.8★★★★★ | 4.4★★★★☆ |
| Accuracy | True RMS | True RMS, ±0.5% basic DC V |
| Safety rating | CAT III 600V | CAT III 600V |
| Auto-ranging | Yes | Yes |
| Best for | Electricians, serious hobbyists | Field techs on branch circuits, drives and HVAC |
| Safety category | CAT III 600V | CAT III 600V |
| Display | 6,000 counts + 33-segment bar graph | 6,000 (datasheet) or 4,000 (extech.com) counts |
| DC volts accuracy | ±(0.5% + 2) | ±(0.5% + 3) on volt ranges, per manual |
| AC volts accuracy / band | ±(1.0% + 3), 45–500 Hz | ±(0.8% + 3), 45–400 Hz |
| LoZ input | AutoVolt, about 3 kΩ, AC or DC | 3 kΩ, AC only, ±(1.2% + 5) |
| Low-pass filter | No | Yes, ±(4.0% + 3); cut-off not stated |
| Non-contact voltage | VoltAlert | Yes, NCV switch position with LED |
| Lowest current range | 6 A (1 mA steps) | 600.0 µA (0.1 µA steps) |
| Temperature | No | Type K, -40 to 1000°C |
| Capacitance / frequency | 9,999 µF / 50 kHz | 60.00 mF / 10 MHz |
| Resistance | To 40 MΩ | 60 MΩ (datasheet, manual) or 40 MΩ (extech.com) |
| Battery | One 9 V, 400 h typical | 2 × AA (manual) or 2 × AAA (extech.com), 130 h |
| Weight | 550 g | 370 g (datasheet) or 407 g (manual) |
| Warranty | 3 years | 3 years |
Specs checked against manufacturer documentation and official Amazon listings. Fluke 117 is hands-on tested by OhmSavvy; the Extech EX355 assessment is desk research. How we research.
Key differences
- →Only the EX355 has a low-pass filter for variable-frequency drive outputs; Fluke lists none on the 117.
- →The EX355 measures from a 600.0 µA range with 0.1 µA steps; the 117's smallest current range is 6 A.
- →The EX355 has a Type K temperature input; the 117 has none (Fluke gives temperature to the 116).
- →The 117's AutoVolt LoZ reads AC or DC; Extech specifies the EX355's LoZ for AC only and asks you to let the meter settle 10 minutes afterward.
- →Fluke specifies the 117's AC volts to 500 Hz; Extech specifies the EX355 to 400 Hz.
- →Extech's own documents disagree on the EX355's count, resistance range, battery type and weight; Fluke's 117 specs are consistent.
A drive feeding a pump motor: the EX355's LPF position
A variable-frequency drive builds its output from fast PWM pulses. A True RMS meter without a filter reads the energy in those pulses as well as the fundamental the motor responds to, so the number it shows on a drive output is generally higher and less stable than the voltage that matters. That is the job the EX355's LPF switch position exists for: set the dial to LPF, choose AC, hold the LPF button for two seconds and the meter filters before it measures. Fluke lists no low-pass filter for the 117.
Extech doesn't publish the filter's cut-off frequency, and it gives the LPF function a looser accuracy than plain AC volts: ±(4.0% + 3 digits) on the 600.0 V range, as we read the manual's table. Worked example on that spec, for an illustrative 230 V motor running at reduced speed: a 230.0 V reading carries ±(9.2 + 0.3) = ±9.5 V. That is coarse, but it answers the field question, which is whether the drive is delivering a sensible voltage for the commanded speed and whether the three phases agree.
If drive work is a daily task rather than an occasional one, a meter with a published filter frequency is the better tool. Our Fluke 117 vs Fluke 87V comparison covers the step up to a meter whose filter Fluke specifies at 3 dB at 1 kHz.
A no-heat call: flame sensor current and supply-air temperature
The second split is everything below an amp. The 117 measures current on 6 A and 10 A ranges only, so its smallest step is 1 mA. The EX355 starts at a 600.0 µA range and steps through 6000 µA, 60.00 mA and 600.0 mA before the amp ranges. Extech gives the microamp ranges ±(0.7% + 2 digits) DC.
On a furnace that lights and then drops out, flame-rectification current is the first number to check, and it is typically a few microamps (your furnace maker states the minimum for that control). Worked on the EX355 spec for an illustrative 3.0 µA reading: ±(0.021 + 0.2) = about ±0.22 µA, which is fine enough to see whether the signal clears the maker's threshold. The 117 shows 0.000 A on the same circuit. The EX355 then reads supply- and return-air temperature on its Type K input, where the 117 has no temperature function.
Bars use a logarithmic scale: each step is ten times the last.
For HVAC-specific picks, see the best multimeter for HVAC technicians, and for the measurement itself, how to measure microamps.
Where the 117 earns its price: AutoVolt and clean specs
Both meters can kill a phantom reading, but the 117's AutoVolt input, at about 3 kΩ, decides AC or DC by itself. The EX355's Lo Z position is specified for AC volts only, and Extech's manual adds a condition we haven't seen on other meters: allow the meter to stabilize for 10 minutes after using LoZ. On a service call where you swing between LoZ checks and ordinary readings, that note is worth knowing before you buy. Its LoZ accuracy is ±(1.2% + 5 digits).
The other advantage is that Fluke's numbers agree with each other. Extech's datasheet says the EX355 is a 6,000-count, 60 MΩ meter on two AA cells weighing 370 g; extech.com's table says 4,000 counts and 40 MΩ, its web copy says AAA, and the manual gives 407 g. The meter face in the Amazon photo shows a 600.0 V reading, which suggests a 6,000-count display, but we report the conflict rather than pick one. On plain AC volts the EX355 is specified slightly tighter, ±(0.8% + 3) against the 117's ±(1.0% + 3), across a narrower 45–400 Hz band.
How we judged these
Field calls side by side
| Call | Fluke 117 | Extech EX355 |
|---|---|---|
| Quick live check at a junction box | VoltAlert | NCV dial position with LED |
| Ghost voltage on a DC control circuit | AutoVolt reads DC | LoZ is AC only |
| VFD output to a pump motor | No filter | LPF, ±(4.0% + 3), cut-off not stated |
| Flame sensor at 3 µA (illustrative) | Reads 0.000 A | 600.0 µA range, about ±0.22 µA |
| Supply-air temperature | No input | Type K, -40 to 1000°C |
| Large drive capacitor, 12,000 µF | Over its 9,999 µF limit | Within 60.00 mF, ±10% |
| Service entrance | Not rated (CAT III 600V) | Not rated (CAT III 600V) |
For an HVAC or light-industrial service tech the EX355 covers more calls for half the money. The 117 is the better fit when the work is wiring rather than equipment. If you want the 117's workflow with more range, compare it with the Fluke 179, which adds temperature and CAT IV but drops VoltAlert and LoZ.
Both meters are CAT III 600V
Choose the Fluke 117 if…
- ✓You want LoZ that reads AC or DC without changing switch position
- ✓Your work is branch-circuit troubleshooting rather than drives or HVAC controls
- ✓You want consistent published specs and a long 9 V battery life
Choose the Extech EX355 if…
- ✓You read variable-frequency drive outputs and need a low-pass filter
- ✓You check flame sensors or controls in µA and mA
- ✓You want supply- and return-air temperature from the same meter
Neither if…
Your drives or PV systems run above 600 V or you work at the service entrance. Both meters stop at CAT III 600V; the Hioki DT4256 and Fluke 87V carry CAT IV 600V / CAT III 1000V with low-pass filters.
The bottom line
For field technicians who service drives, rooftop units and furnaces, the Extech EX355 is the better buy: it matches the Fluke 117's LoZ, NCV and CAT III 600V rating and adds a low-pass filter, microamps and temperature at about half the price. Choose the Fluke 117 for electrical troubleshooting where AutoVolt on AC and DC and consistent, well-documented specs matter more than extra functions.
Frequently asked questions
Does the Fluke 117 have a low-pass filter for VFDs?+
No. Fluke doesn't list a low-pass filter for the 117, so on a drive's PWM output it reads the carrier energy along with the fundamental. The Extech EX355 has an LPF position for variable-frequency voltage, specified at ±(4.0% + 3 digits) on its 600 V range. For a filter with a published cut-off, look at the Fluke 87V or the Hioki DT4256.
Is the Extech EX355 6,000 or 4,000 counts?+
Extech's sources disagree. The EX350 Series datasheet lists the EX355 at 6,000 counts and the EX350 at 4,000, while the table on extech.com shows 4,000 for the EX355. The manual's range table uses 6,000-count ranges such as 600.0 V and 60.00 mA for the EX355, which supports 6,000, but we report both figures.
Can the Extech EX355 detect ghost voltage on DC circuits?+
Extech's manual describes the EX355's Lo Z position as an AC voltage measurement at about 3 kΩ, so it isn't specified for DC. The Fluke 117's AutoVolt input sits at about 3 kΩ and selects AC or DC automatically. Extech also says to let the EX355 stabilize for 10 minutes after using LoZ mode.
Which meter is better for HVAC work?+
The Extech EX355 on published specs. It reads flame-sensor current on a 600.0 µA range, measures temperature with a Type K probe from -40 to 1000°C, reads large capacitors to 60.00 mF and filters drive outputs. The Fluke 117 has no µA range, no temperature and no filter, though it remains a strong meter for the electrical side of a call.
What batteries does the Extech EX355 use?+
Extech's manual and datasheet say two AA batteries, with about 130 hours of typical life on alkalines, while the extech.com product page lists two AAA cells. Go by the manual if you are buying spares, and check the battery compartment when the meter arrives. The Fluke 117 uses one 9 V battery rated for about 400 hours.
Are both meters safe on a 480 V panel?+
Both are rated CAT III 600V and read up to 600 V, which covers a 480 V distribution panel. Neither carries a CAT IV rating, so neither is rated for the service entrance or meter base. Use leads with matching ratings, wear the PPE your arc-flash labeling calls for, and leave utility-side work to a licensed electrician.
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