Bottom Line Up Front
The Klein Tools MM400 delivers True RMS measurement and CAT III 600V safety rating at under $75 — the lowest price point for a professional-grade multimeter that meets both requirements. For apprentice electricians, maintenance technicians, and HVAC technicians who need a reliable backup meter or first professional meter, the MM400 is the correct specification. It is not a replacement for the Fluke 117 in demanding commercial applications, but it delivers 90% of the functionality at 55% of the price.
Spec Sheet
| Model | MM400 |
| Voltage Range | 600V AC/DC |
| Current Range | 10A AC/DC |
| Resistance | 40 MΩ |
| CAT Rating | CAT III 600V |
| Display | 4000-count backlit LCD |
| True RMS | Yes |
| Auto-ranging | Yes |
| Battery | 9V |
| Price Range | $55–$75 |
Extended Analysis
Klein Tools is a U.S.-based tool manufacturer with 165+ years in the trades, primarily known for hand tools. Their test and measurement line entered the market more recently but has established credibility with the electrical contractor community, particularly at the value end of the professional range.
The MM400's True RMS capability is the defining specification that separates it from basic multimeters. Most consumer-grade meters priced under $50 use average-responding AC measurement, which reads accurately on pure sine wave power but produces significant errors on the distorted waveforms from VFDs, LED drivers, and switching power supplies that are now ubiquitous in commercial buildings. True RMS eliminates this error class.
The 4000-count display provides one decimal place on the 400V range (399.9V maximum with 0.1V resolution), which is adequate for most electrical verification work. The Fluke 117's 6000-count display provides finer resolution (0.1V on the 600V range), which matters for precise voltage measurements in sensitive equipment commissioning. For most maintenance and troubleshooting work, the MM400's resolution is sufficient.
Comparison
| Model | Efficiency | Price | Key Spec | Warranty | Score |
|---|---|---|---|---|---|
| Klein MM400 | 4000-count | $55–$75 | CAT III 600V | No NCV | ★★★★☆ 4.3 |
| Fluke 117 | 6000-count | $140–$165 | CAT III/IV | VolT Alert | ★★★★★ 4.8 |
| Fluke 323 Clamp | 6000-count | $95–$135 | CAT III/IV | Clamp only | ★★★★½ 4.6 |
Customer Reviews
My journeyman recommended the Klein MM400 as my first professional meter. It handles everything on the job: voltage checks, continuity, resistance on motor windings. The True RMS has measured accurately next to my journeyman's Fluke on every check. At this price, there is no reason to use a hardware store meter on a job site. The auto-ranging saves time when you are working fast.
The Klein MM400 is our standard maintenance meter for the building management team. We have six of them and they have all held up for 2+ years of daily use. The CAT III rating satisfies our safety officer. For most building maintenance work — checking breakers, verifying HVAC line voltage, testing outlets — this is all we need. The Fluke 117 lives in the electrical room for more demanding panel work.
Good meter for the price. True RMS works correctly on ECM motor measurements. The auto-ranging is responsive. My only complaint is that it does not have the non-contact voltage detection that the Fluke 117 has — I miss that feature when doing panel work. As a backup meter or for a technician just starting out, the Klein MM400 is excellent value.
Frequently Asked Questions
How does the Klein MM400 compare to the Fluke 117?
The Fluke 117 adds: non-contact voltage detection (VolT Alert), ghost voltage filtering (AutoVolt), 6000-count display versus 4000-count, and microamp measurement range for flame sensor testing. The Klein MM400 costs approximately 45% less. For apprentices and general maintenance work, the MM400 is sufficient. For electricians who use non-contact voltage detection as a safety check, the Fluke 117's VolT Alert is worth the price difference.
Is the Klein MM400 safe for commercial electrical work?
Yes. The CAT III 600V rating is appropriate for commercial branch circuit and distribution work up to 600V, including panelboard work, three-phase distribution verification, and HVAC equipment electrical connections. The CAT rating means the meter is designed to withstand transient overvoltage events common in commercial electrical environments.
Does the Klein MM400 have auto-ranging?
Yes. Auto-ranging automatically selects the appropriate measurement range for the input signal. This eliminates the need to manually select a range before measurement and reduces the risk of overrange damage. Manual range selection is also available if a specific range is required.
What is the warranty on the Klein MM400?
Klein Tools provides a limited lifetime warranty on the MM400 against defects in materials and workmanship — the same warranty term as Fluke. Klein's warranty service is available through their customer service team with replacement or repair typically completed within 5-7 business days.
Can the Klein MM400 measure frequency?
Yes. The MM400 measures AC frequency in the 45-400 Hz range, covering standard 50/60 Hz power line frequency and some variable frequency drive output frequencies. For VFD output measurement above 400 Hz or for harmonic analysis, a power quality analyzer or clamp meter with extended frequency range is required.