Understanding CAT Safety Ratings and IP,NEMA Ratings for Current Transformers
What are Electrical Parameters?
Electrical parameters are specific characteristics associated with devices that use or move electricity. These include various ratings and codes, such as CAT ratings and Ingress Protection (IP and NEMA) codes, which comply with standards set by professional teams. Understanding an asset's electrical parameters is crucial for testing its performance and ensuring safety for both the asset and its users. Examples of electrical parameters include impedance, inrush current, power factor, and voltage drop.
What are Current Transformers CAT Ratings?
Current transformers are rated for different electrical parameters, necessitating the need to check for appropriate CAT ratings, IP and NAMA codes, and independent verification symbols. These ensure that the transformers have undergone independent laboratory testing and are safe for your measurements.
When selecting an Overvoltage Installation Category rating (CAT II, CAT III, or CAT IV), it's important to choose a tool rated for the highest potential category of use. Additionally, the voltage rating should match or exceed the intended situations. CAT-rated meters are designed to reduce the risk of arc flash inside the meter, with ratings typically located near the input jacks.
For example, if you're measuring a 480-V electrical distribution feeder panel, you should use a current transformer rated at least CAT III-600 V. In this case, a CAT III-1000 V or CAT IV-600 V transformer would also be suitable.
There are four levels defined by the type of load to be measured
CAT I : Electronic Devices
Anything from a small circuit board to larger device with high-voltage but low-energy
CAT II : Single-Phase AC Loads
Appliances or portable tools
CAT III : Three-Phase Distribution
Some large building lighting systems and polyphase motors
CAT IV : Three-Phase Utility Connections or Outdoor Conductors
Electrical meters, outdoor connections, any low-voltage and high-energy connection
Within these four levels, the IEC has setup transient test guidelines for each category.
If we extend this to calculate the current for the working and transient voltages, you’ll see that even though two CAT ratings cover the same working voltage, that does NOT mean they are an equal.
Comparison of NEMA and IP Protection Levels
When discussing the protection levels of enclosures or electronic equipment, the first thing that often comes to mind is the IP (Ingress Protection) level. However, in the United States, there is another standard for indicating protection levels, known as NEMA. So, what are the differences between IP protection levels and NEMA levels?
NEMA protection levels are enclosure protection standards for industrial control devices and systems, defined by the National Electrical Manufacturers Association (NEMA) in the United States. These standards encompass protection against dust, water, and explosion, going beyond what is covered by the IP codes, which include only dust and water protection.
The IP protection level system is established by the International Electrotechnical Commission (IEC). IP stands for Ingress Protection, and IP ratings indicate the level of protection an electrical equipment enclosure offers against the intrusion of foreign objects. The source of this standard is IEC60529, adopted as a national standard in the United States in 2004. IP protection levels are indicated by two numbers: the first number represents the level of dust protection, while the second number signifies the level of water protection.
What do the numbers in IP or NEMA ratings signify?