Reference
IP and CAT ratings explained
Two codes on almost every instrument datasheet. One says how well it survives dust and water, the other says where on the electrical system it is safe to measure.
IP code (IEC 60529)
Written as IP followed by two digits, for example IP54. The first digit is protection against solid objects and dust (0 to 6). The second is protection against water (0 to 9). An X replaces a digit that was not tested, as in IPX4. The rating IPX9K or IP69K, often seen on wash-down equipment, comes from DIN 40050-9 and ISO 20653 (road vehicles), not from the base IEC 60529 table.
| Digit | Protected against |
|---|---|
| 0 | No protection |
| 1 | Objects over 50 mm (back of a hand) |
| 2 | Objects over 12.5 mm (a finger) |
| 3 | Objects over 2.5 mm (tools, thick wire) |
| 4 | Objects over 1 mm (thin wire) |
| 5 | Dust protected (limited ingress, no harmful deposit) |
| 6 | Dust tight (no ingress) |
| Digit | Protected against |
|---|---|
| 0 | No protection |
| 1 | Vertically dripping water |
| 2 | Dripping water, enclosure tilted up to 15 degrees |
| 3 | Spraying water, up to 60 degrees from vertical |
| 4 | Splashing water from any direction |
| 5 | Water jets (6.3 mm nozzle) |
| 6 | Powerful water jets (12.5 mm nozzle) |
| 7 | Temporary immersion, up to 1 m for 30 minutes |
| 8 | Continuous immersion, to conditions the maker states |
| 9 | High-pressure, high-temperature water jets (about 80 °C) |
IP ratings describe the enclosure, not the whole instrument in use. A case that is rated closed may not be rated with the battery door open or a probe plugged in. See the IP rating guide.
CAT rating (IEC 61010-1)
The measurement category tells you how much energy sits behind the point you are measuring. The closer to the supply source, the higher the available fault current and the larger the transients, so the higher the category you need. A meter rated CAT III 600 V is built to survive the transients of that location at up to 600 V. It is not a CAT IV meter.
| Category | Location | Typical examples |
|---|---|---|
| CAT I | Protected electronic circuits and signal-level equipment | Circuits not directly connected to mains, or protected by limiting devices |
| CAT II | Single-phase receptacle-connected loads | Appliances, portable tools, socket outlets on long branch circuits |
| CAT III | Fixed installation, distribution level | Distribution boards, bus bars, feeders, motors on fixed wiring |
| CAT IV | Origin of the installation | Service entrance, meter, primary overcurrent protection, overhead and underground supply lines |
Impulse withstand by category and rated voltage
Peak transient the instrument is designed to survive, for the common rated voltages.
| Rated voltage | CAT II | CAT III | CAT IV |
|---|---|---|---|
| 300 V | 2.5 kV | 4 kV | 6 kV |
| 600 V | 4 kV | 6 kV | 8 kV |
| 1000 V | 6 kV | 8 kV | 12 kV |
The category tests also differ in source impedance (lower for CAT III and IV than for CAT II), so a CAT II 1000 V meter is not equivalent to a CAT III 600 V meter even where both quote 6 kV. A higher voltage number does not make up for a lower category. CAT III 300 V withstands a smaller transient than CAT III 600 V, and CAT IV 300 V and CAT III 600 V both withstand 6 kV but are meant for different locations. Pick the category of the location first, then a voltage rating at or above the system voltage. Read the full CAT rating guide.
Tables summarise the published codes. Check the marking on your own instrument and the current edition of the standard before relying on any rating for safety.
Browse the standards directory → Multimeters → Clamp meters →
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