The IEC (International Electrotechnical Commission) has designated four categories with regards to the protection of multimeters. The CAT-IV rating is the highest of these and pertains to devices that have the necessary electronic circuitry to withstand a voltage surge at a given test voltage.
These meters can measure systems in industry at the substation and below, including switchgear, circuit breakers, panel boards, motor control, socket outlets, and so on. A CAT-IV multimeter rated to 600V would theoretically be able to handle an 8kV surge caused by faulty machinery or from a lightning strike, for example. A CAT-IV meter rated to 300V would be good for 6kV on 300V installations.
Categories III, II and I will handle progressively lower energy surges.
| Voltage Rating | Category II Peak | Category III Peak | Category IV Peak |
|---|---|---|---|
| 100V | 800V | 1500V (1.5kV) | 2500V (2.5kV) |
| 150V | 1.5kV | 2.5kV | 4kV |
| 300V | 2.5kV | 4kV | 6kV |
| 600V | 4kV | 6kV | 8kV |
| 1000V | 6kV | 8kV | 12kV |
What Makes a Multimeter CAT-IV?
Current inputs should be protected by HRC fuses. These high rupture capacity fuses are well-engineered, fast-blow type that are filled with sand. Technically, any meter that doesn’t have HRC fuses is not CAT-IV-rated. Glass fuses are not man enough to put up with high current surges.
That’s not the end of the story as a fuse alone will not offer total protection of the meter and user. Category IV meters should also have defense at the electronic component level, to include MOVs (metal oxide varistors), power resistor and PTC (positive temperature coefficient) resistors. Some of the cheaper meters with a CAT-IV spec may only have some of these or none at all.
It also goes without saying that the meter should be mechanical sturdy with regard to its input jacks, leads and casing. Not all test leads are to CAT4 standard, so that is another thing to keep an eye on when buying into this rating.
Multimeters Rated to Category IV
Most of the mid-range and up Flukes are CAT-IV rated. The only ones with lesser ratings are some of the loop calibrators (which don’t need that level of protection) and the Chinese-made 110 and 100 series – these are cheaper models. Although still well made with good build quality and features, they don’t have the level of input protection required to meet CAT-IV surge energies.
There are some cheaper American brands that produce acceptable quality meters and also one or two Asian ones.
High Quality CAT-IV Fluke Multimeters
The Fluke 87V is a high end, full size meter and one of the best in the business of any category. It boasts excellent functionality, features, reliability and durability and is equally well protected internally. It is CAT-IV-rated to handle 600V installations and can withstand surges to 8kV.
This is a solid meter for both electrical and electronic applications, with True RMS capability and a current-handling capacity to 20A. Other main pluses include a high resolution display (to 20,000 counts), auto-touch hold, various modes and a high level of accuracy (0.05% DC volts). See the full review of the Fluke 87V here. Other meters in the Fluke 80 Series are also to CAT-IV, including the excellent automotive-centric 88V.
The Fluke 179 is another very good True RMS multimeter, which has a sleek design and extensive functionality. It does not have the breadth of ranges or as many useful functions as the 87V – and is without micro-amps, some modes and a lesser accuracy – but it does have a CAT-IV rating and can be used to measure the same high energy circuits.
Other popular Fluke CAT-IV Multimeter contenders: The 287/289 data loggers, the 3000FC wireless data logger, the 233 with detachable display, the thermal imaging 279FC, the 1587 insulation tester, the rugged Fluke 77IV, and the heavy duty, watertight 20 series (to include the 28II). All these are excellent devices with solid build, specs and level of safety. Fluke also make CAT-IV-rated, amp clamp multimeters, like the dependable 323.
Few other brands come as close regards to the level of protection that they provide. Agilent (now Keysight) are one of the ones that are on a level pegging, albeit their higher end handheld meters, which tend to be more expensive again, such as the Agilent U1253B.
Other American Made
Aside from Fluke and Agilent, there are a few standout brands that offer the right ratings. Extech is a quality brand out of New Hampshire that produces good mid-level devices with impressive displays. The Extech EX360 is one of their top models that sells well and comes with a CAT4 rating.
Amprobe is one of the best known meter makers of digital multimeters, establishing their name through clamp meters originally. Most of the AM-500 Series are CAT-4, including the excellent Amprobe AM-570 and AM-530 models.
Klein Tools is another long-running American firm that puts out quality measuring equipment to go with their huge catalog of good tools. The general purpose Klein MM1000 and industrial strength MM6000 are both CAT-IV.
Asian Brands
Of the many Asian multimeter manufacturers, the only one that can really approach this level of protection is Brymen. The Brymens are very well made, including the BM257 and the rebranded EEVBlog Brymen BM235. Both are rated to CAT-IV, albeit to 300V, with a CAT-III rating of 600V. These are more expensive than the typical lesser-branded meters with similar specs, but the proof is in the pudding regards their actual category rating. Brymen are OEM’d by Greenlee in the US.
There are some okay Chinese multimeter brands. Mastech, Tekpower, Sinometer and Uni-T are all quite decent. They’re not as blasé as they used to be regards spurious ratings – often touting CAT-IV, when in reality CAT-III, or even CAT-II, would be more suitable judging by the lack of quality components. The UNI-T UT61E is one such example. While a good meter for the price, its rating should be taken with a pinch of salt.
Price
Generally, promotions aside, anything for under $100 likely won’t have the required input protection to withstand the potential surge transients that a CAT-IV designation suggests. Spend this amount on a Fluke and you still won’t get it. Their CAT-IV meters typically start from around $250. But you are assured the best protection money can buy.
Conclusion
Category ratings are not there for decoration, or something you don’t need to be overly concerned with. It is serious business for those working in heavy industry especially.
If unsure on what CAT-IV multimeter to buy and you have the pockets, go with Fluke. You won’t be disappointed. Along with excellent protection, you also get great specs, accuracy and speed. Those more budget-oriented could save and go with one of the better Amprobe, Klein, Extech or Brymen meters. You might lose some functionality and speed, but will remain well protected.
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