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Fluke · Fluke 355 True RMS Clamp-Meter, 2,000A AC/DC, Conductors to 58mm, Voltage, Frequency, and Resistance Measurement
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Verdict
The Fluke 355 is a specialist instrument: a True RMS clamp that reads AC and DC current to 2000 A through a 58 mm jaw. It also measures AC voltage to 600 V, DC voltage to 1000 V, frequency to 1 kHz and resistance to 400 kΩ, has an inrush function for motor starts, and is rated CAT IV 600 V and CAT III 1000 V under IEC 61010-2-032. The jaw is the point. Standard industrial clamps stop at 1000 A and a jaw in the 30 to 40 mm range; the 355 fits a large feeder, a bundle of parallel cables or a DC bus and reads the lot. For anyone who does not regularly see currents above 1000 A, it is heavy, bulky and more than needed. For switchboard, generator, DC drive and electrochemical work, the documentation supports it as the rigid-jaw option at this current level.
Who It Is For
- Switchgear and main distribution electricians measuring feeder currents.
- Generator and marine technicians checking alternator and battery bus currents.
- Industrial teams working on DC drives, rectifiers and welding supplies where DC current is high.
Documented Specifications
| Item | Documentation |
|---|---|
| Current | AC and DC to 2000 A, True RMS |
| Jaw opening | 58 mm (2.3 inches), fits large or multiple conductors |
| Voltage | AC to 600 V, DC to 1000 V |
| Frequency | To 1 kHz |
| Resistance | To 400 kΩ |
| Inrush | Surge current at motor and inductive load start-up |
| Safety rating | IEC 61010-2-032, CAT IV 600 V, CAT III 1000 V |
The 58 mm Jaw and Multiple Conductors
Above a few hundred amps, cables are run in parallel: two, three or four conductors per phase. Measuring one and multiplying assumes equal sharing, which is exactly the assumption an electrician often needs to check. A 58 mm jaw encloses the whole set so the reading is the total phase current, and clamping each conductor individually then shows whether the sharing is balanced. The jaw also fits the large single conductors and cable lugs at a generator or transformer. Because the 355 uses a Hall-effect sensor for DC, the jaw should be zeroed with nothing in it before a DC measurement, and readings on a conductor that is not centred in the jaw carry more error than on a small clamp. The general technique is in measuring current with a clamp meter.
DC Current and Inrush
Flexible Rogowski probes such as the iFlex read very high AC currents conveniently, but they cannot read DC. That leaves the rigid Hall-effect clamp as the tool for battery banks, DC drives, electroplating and welding circuits at high current, which is where the 355 has few alternatives in a handheld. The inrush function captures the start-up surge of a motor or transformer, which on a large machine can be many times the running current, and lets the electrician compare it with the protection settings. The 1 kHz frequency range covers mains, generator and most drive fundamental frequencies.
Voltage Functions and Safety Rating
The voltage functions are secondary but complete: 600 V AC, 1000 V DC and resistance to 400 kΩ mean the meter can confirm a supply and check a coil without a second instrument. The CAT IV 600 V and CAT III 1000 V rating under the clamp-specific standard IEC 61010-2-032 means it is designed for the transient environment of the service entrance and of 1000 V distribution, which is where 2000 A conductors are found. See choosing a clamp meter for what the categories mean. Owners describe the 355 as a meter that lives in the van for the jobs that need it rather than in a pouch, which is the right expectation for its size and price class. When clamping parallel conductors, all of them must belong to the same phase; including a conductor of another phase gives a meaningless total.
Strengths
- 2000 A AC and DC in a handheld with a documented rating.
- 58 mm jaw fits large feeders and parallel bundles.
- Inrush capture and a wide resistance range.
- Reads DC at currents flexible probes cannot.
Limitations
- Large and heavy; awkward for everyday panel work.
- No wireless logging or remote display.
- Hall-effect DC readings need zeroing and conductor centring.
How It Compares
The Fluke 381 reaches 2500 A AC with its included iFlex and adds a remote display, but its rigid jaw stops at 1000 A and the iFlex is AC only. The Extech MA1500 reads 1500 A AC and DC through a much smaller jaw at a lower price. The Extech EX840A is the 1000 A alternative with inrush and a low-pass filter.
How We Research
This review is based on the manufacturer’s published specifications, the Amazon product listing and owner reports. We did not run laboratory tests.
Recommended Tools
Products shown because their documented specifications fit this guide. Price and availability are on Amazon and can change.
Frequently Asked Questions
When is a 2000 A clamp needed?
On main switchboard feeders, large motor supplies, generator outputs, welding circuits and DC bus work where currents exceed the 1000 A limit of standard industrial clamps.
Why is the jaw 58 mm?
High-current conductors are physically large, and parallel feeders are often run as multiple cables per phase. A 58 mm opening fits a large single conductor or a bundle so the total current can be read at once.
Is a flexible probe a substitute?
For AC, an iFlex or similar Rogowski probe reaches busbars and reads high currents. The 355 is needed when the current is DC, which flexible probes cannot measure, or when a rigid, rated instrument is preferred.
What is the inrush function for?
It captures the surge when a motor or other inductive load starts, so the start-up current can be compared with the protection settings and the motor rating.
Affiliate disclosure: Akermin earns a commission from qualifying Amazon purchases made through links on this page. Our editorial picks are based on documented specifications and owner feedback, not commissions.
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