On the right of the image a DiLog CombiVolt Tester is being proved using a DiLog PU690 Proving Unit. The proving unit is hanging on the wall in a black fabric case with a clear, plastic window through which the PU690 can be seen and accessed. On the left of the image it reads 'What Are CAT Ratings?' in white and yellow block lettering.

In summary, CAT ratings are overvoltage categories; they are safety ratings that indicate the types of electrical environments in which test and measurement instruments can be safely used. Understanding these categories is crucial to ensuring that you select the correct tool when working on an electrical installation.[1]

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Why Are CAT Ratings Important?

Simply, to protect yourself against electric shocks and arc blasts caused by high-energy transients. Arc blasts injure more people every year than electric shocks. However, both disasters can be averted by ensuring you use an electrical test and measurement instrument that is properly insulated and equipped to deal with the energy of overvoltage transients likely to occur in the distribution system. The more complex the distribution system and loads, the more likely you are to encounter high-energy transient overvoltages.

What’s the Difference Between CAT Ratings?

CAT ratings are overvoltage categories that denote the instrument’s resistance to high-energy transients and its ability to withstand them.

The CAT number refers to the power of the electrical environment and the energy of the transients likely to be encountered in that circuit; the greater the CAT number the more resistance the meter provides, making it suitable for use on higher power circuits with higher energy transients. For instance, an instrument with a CAT III rating is resistant to higher energy transients than an instrument with a CAT II rating.

Black and yellow table detailing the differences between overvoltage categories with examples.
Table is taken from Fluke's Application Note, ABCs of Multimeter Safety.

The voltage rating that follows the CAT number indicates the tester’s ability to withstand transients. The higher the voltage the better the tester is at withstanding transients. For example, a CAT III 1000V meter offers better protection than a CAT III 600V meter. It is important to note that voltage ratings are only directly comparable when instruments share the same CAT category. For instance, a CAT II 1000V tester will offer greater protection than a CAT II 600V tester, but it will not offer as much protection as a CAT III 600V tester despite having a higher voltage rating.

Work Safely

Making sure that you’re using a tester with an appropriate overvoltage rating is just one of the precautions that must be taken to ensure you are working safely. You should also use appropriate PPE, for example, insulated gloves, boots, mats, safety goggles, and/or a face shield; follow proper measurement protocols; and observe correct safe isolation and lockout tag-out procedures.

Read more about Safe Isolation

Di-log DLPK6790 CombiVolt 2 & PU690V Proving Unit Kit
DiLog DLPK6790 CombiVolt 2 & PU690V Proving Unit Kit

To help you maintain compliance with safe isolation and lockout tag-out regulations, PASS Ltd is offering a free DiLog DLL0C3/ DLL0C4 Lockout Kit with DiLog’s DLPK9780 and DLPK6790 Safe Isolation Kits.

The aforementioned safe isolation kits include a DiLog DL6780 CombiVolt 1 or DL6790 CombiVolt 2 Voltage and Continuity Tester, PU690 690V AC Proving Unit, and a bespoke carrying pouch. The DiLog PU690 690V Proving Unit is the only proving unit on the market to offer a CAT II 750V safety rating; it can test high- and low-impedance instruments making it suitable for use with voltage testers, like DiLog’s CombiVolt Testers, and multimeters.

The Di-log DLPK6780 CombiVolt 1 being proved using the Di-log PU690V Proving Unit.
The DiLog DLPK6780 CombiVolt 1 is being proved using the DiLog PU690V Proving Unit.

DiLog's DLL0C3 18th Edition Professional Lockout Kit (worth £67.79 ex VAT) and DLL0C4 18th Edition Expert Lockout Kit (worth £83.79 ex VAT) include an array of padlocks, hasps, lockout devices, and labels perfect for implementing effective lockout tag-out procedures in the workplace. Simply select your free kit before you add your DiLog Safe Isolation Set to your basket.

DiLog DLL0C3 18th Edition Professional Lockout Kit including a black DiLog Soft Case, 'Do Not Operate' labels, a felt pen, red lockout padlock and key, red lockout hasps, and red MCB lockout devices.
DiLog DLL0C3 18th Edition Professional Lockout Kit
DiLog DLL0C4 18th Edition Expert Lockout Kit including a black DiLog Soft Case, 'Do Not Operate' labels, a felt pen, red lockout padlock and key, red lockout hasps, and red, yellow, and blue MCB lockout devices.
DiLog DLL0C4 18th Edition Expert Lockout Kit

Further Information

Please contact our Sales team on 01642 931 329 or via our online form for help and advice regarding our eclectic range of safe isolation and lockout tag-out products, including DiLog’s DLPK6780 and DLPK6790 Safe Isolation Kits.

For a detailed explanation of overvoltage (CAT) categories, please download Fluke’s application note, ABCs of multimeter safety.   


[1] All the information for this blog was gathered using the following sources: