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.

Measurement Category	Working Voltage	Transient Voltage	Test Source (Impedance)
CAT I	150V	800V	30 Ohms
CAT I	300V	1500V	30 Ohms
CAT I	600V	2500V	30 Ohms
CAT I	1000V	4000V	30 Ohms
CAT II	150V	1500V	12 Ohms
CAT II	300V	2500V	12 Ohms
CAT II	600V	4000V	12 Ohms
CAT II	1000V	6000V	12 Ohms
CAT III	150V	2500V	2 Ohms
CAT III	300V	4000V	2 Ohms
CAT III	600V	6000V	2 Ohms
CAT III	1000V	8000V	2 Ohms
CAT IV	150V	4000V	2 Ohms
CAT IV	300V	6000V	2 Ohms
CAT IV	600V	8000V	2 Ohms
CAT IV	1000V	12000V	2 Ohms

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.

Measurement Category	Working Voltage	Transient Voltage	Test Source (Impedance)	Working Current	Transient Current
CAT I	150V	800V	30 Ohms	5A	26.6A
CAT I	300V	1500V	30 Ohms	10A	50A
CAT I	600V	2500V	30 Ohms	20A	83.3A
CAT I	1000V	4000V	30 Ohms	33.3A	133.3A
CAT II	150V	1500V	12 Ohms	12.5A	123A
CAT II	300V	2500V	12 Ohms	25A	208.3A
CAT II	600V	4000V	12 Ohms	50A	333.3A
CAT II	1000V	6000V	12 Ohms	83.3A	500A
CAT III	150V	2500V	2 Ohms	75A	1250A
CAT III	300V	4000V	2 Ohms	150A	2000A
CAT III	600V	6000V	2 Ohms	300A	3000A
CAT III	1000V	8000V	2 Ohms	500A	4000A
CAT IV	150V	4000V	2 Ohms	75A	2000A
CAT IV	300V	6000V	2 Ohms	150A	3000A
CAT IV	600V	8000V	2 Ohms	300A	4000A
CAT IV	1000V	12000V	2 Ohms	500A	6000A

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?

Ingress Protection (IP)

Both IP and NEMA are broke down in this link: IP code - Wikipedia

1st Digit: Solid Particle Protection

0	1	2	3	4	5	6
Not protected	Protected against solid objects greater than 50mm	Protected against solid objects greater than 12mm	Protected against solid objects greater than 2.5mm	Protected against solid objects greater than 1.0mm	Dust Protected	Dust tight

2nd Digit: Liquid Ingress Protection

0	1	2	3	4	5	6	6K	7	8	9K
Not protected	Protected against dripping water	Protected against dripping water when tilted up to 15 degrees	Protected against spraying water	Protected against splashing water	Protected against water jets	Protected against powerful water jets	Protected against powerful waterjets with increased pressure	Protected against the effects of submersion up to 1m	Protected against submersion of 1m or more	Protected against powerful high temperature water jets