Right equipment, right location
Posted by: electime 4th August 2022
How understanding installation categories can keep you safe, explains Steve Dunning, managing director of Martindale Electric.
Many electrical products, including vital pieces of testing equipment, are assigned a safety rating commonly known as “CAT”, falling into one of four measurement categories: a classification system determined by the International Electrotechnical Commission (IEC) which tells the user where and how equipment can be used safely.
The four BS EN 61010-1 ‘overvoltage’ categories – CAT I, II, III and IV – define the potential for risk from hazardous transient impulses and potentially lethal short circuits on the mains supply system based on where an individual may be working. The magnitude of risk depends on the amount of damping of the transient energy due to the location within the system as well as the system voltage.
What this means is that each category tells the user whether or not a measurement device, for example, is suitable for use within a particular situation. Just as importantly, the categorisation also indicates where the device may not be suitable for use and could even present a danger to life.
Not only can using equipment outside of its designated safety rating skew the accuracy of test results because it simply isn’t built for use in that application, it can be catastrophic in terms of safety, which is why it’s vital to match the right equipment with the right test location.
Understanding the categories
Measurement Category I refers to measurements performed on circuits not directly connected to the mains supply, or specially protected secondary circuits such as those powered by regulated low-voltage sources.
Measurement Category II refers to measurements performed on circuits directly connected to a low-voltage mains installation and might include standard 13A socket outlets, household appliances, portable tools and equipment.
Measurement Category III refers to measurements performed within a building’s permanent installation: distribution wiring including mains bus, feeders and branch circuits or hard-wired loads.
Measurement Category IV refers to the supply side source of the building’s installation – for measurements performed at the source of the low-voltage installation such as electricity meters and measurements on primary overcurrent protection devices and ripple control units. It also includes devices and locations between the supply side of the building and the source, typically a substation.
Equipment
Matching your test equipment safety rating to the overvoltage category is absolutely critical. What’s more, testers, leads and accessories all need safety ratings equivalent to, or higher than, the overvoltage category and voltage rating in order for the location to be safe.
If, for instance, there is a mismatch between insulation and voltage, or too great a level of current passes through a piece of equipment, the user faces a significant threat from dangerous arcs, for example – but it’s a danger that’s totally preventable with care and attention. When working with electricity, understanding precisely what a tool has been designed for is vital when it comes to staying safe.
Test equipment used for measuring mains circuits will be marked with one or more of three measurement categories: CAT II, CAT III or CAT IV. This categorisation tells you which installations of a mains supply the equipment can be used upon safely.
Each category also has a voltage rating marked to indicate the maximum safe phase to earth system voltage – 50V, 100V, 150V, 300V, 600V or 1000V. Transient impulses are greatest for CAT IV 1000V installations – typically, the higher the category the greater the risk of circuit overload or arcs from transients, for example.
Furthermore, there is a degree of detail to understand within the ratings themselves. For instance, a CAT IV 300V, CAT III 600V marking means that the unit can only safely be used on CAT IV installations where the phase to earth voltage is <300V and on CAT III installations <600V.
Such a unit could safely be connected between phases on CAT IV installations of a 3-phase distribution system where the phase-to-phase voltage is 400V because the phase to earth voltage is 230V.
We know just how important it is to get this detail right – and to match the right equipment with the right job – which is why we continue to invest in our range of industry standard voltage indicators.
Working safely at higher voltages
Martindale’s VI-15000 voltage indicator is designed for higher voltage applications, with a safety rating of 1000V CAT IV – one of the first two-pole indicators rated to this level in the UK. The Martindale VI-15000 also has LED indication for AC/DC voltages from 50V to 690V and above, ensuring compliance with health and safety recommendations for safe working in all BS EN 61010 and BS EN 61243-3 installation categories.
This is now the most straightforward and reliable way to be sure that circuits have been de-energised and properly isolated prior to carrying out any maintenance activities or making modifications. Quite simply, it’s keeping people safe and making it easier than ever to safeguard against risk when working at this level.
Based on the industry endorsed VI-13800, the CAT IV 1000V design not only provides improved protection against voltage transients but also includes a high wattage resistor that will limit the current in the event of damage to the cable in accordance with BS EN 61243-3. The protection is built in where it’s needed – in the handheld probe assembly rather than only in the instrument, providing a far superior level of protection.
If you’re interested in learning more, staying safe and matching the right equipment to the right location visit martindale.tips/CAT-poster
