NEMA ratings and enclosures

For optimal safety and performance, electrical equipment needs to be sheltered from the environment. Both a NEMA rating and an IP rating indicate the level of protection a device has against outside conditions, ranging from falling dust to ocean waves. These two designations differ in their methods, parameters, and categories.

When selecting a pressure sensor or transmitter, one important factor to consider is how well its enclosure or case protects sensors against the elements and possibility of explosions. Common and seemingly innocuous environmental conditions, such as dust or moisture, can lead to errors or malfunctions, both of which negatively impacts performance and safety.

Two organizations make it easy to understand the level of protection a product has. The National Electrical Manufactures Association (NEMA) has come up with many NEMA Enclosure Types, commonly called “NEMA rating,” specifically for electrical equipment. The International Electrotechnical Commission (IEC) has created a numerical system to categorize almost any kind of item that covers or surrounds. Ingress Protection (IP) codes deals with more than just electronic enclosures, and it considers only solids and liquids.

These rating systems are similar in the sense that they classify the quality and quantity of incursions. However, the two use different testing parameters and, thus, are not directly comparable or easily converted. Additionally, IP ratings deal only with ingress, while NEMA ratings are more comprehensive, considering other factors such as corrosion and the instrument’s physical location.
 

What Are NEMA Ratings?

NEMA ratings, widely used in the United States, are based on the NEMA 250 standard “Enclosures for Electrical Equipment (1000 Volts Maximum).” They indicate the level of protection a device has, ranging from falling dust to corrosive media. All NEMA ratings assume that the enclosure protects personnel against hazardous parts.

NEMA ratings 1–6 and 12–13 are for nonhazardous locations, Type 11 deals with corrosion, and Types 7–10 qualify enclosures for hazardous (explosive) locations and also incorporate other industry guidelines, namely Underwriters Laboratories (UL) Class I or II requirements and Mine Safety and Health Administration (MSHA) standards. This table summarizes the most common NEMA ratings:

NEMA Enclosure Types

RATING

DEVICE LOCATION

ENCLOSURE PROTECTS AGAINST…

NEMA 1

indoors

·    falling dirt

NEMA 2

indoors

·    falling dirt

·    dripping and light splashing water

NEMA 3

indoors/outdoors

·    falling dirt, windblown dust

·    rain, sleet, snow

NEMA 3R

indoors/outdoors

·    falling dirt

·    rain, sleet, snow

·    damage from external formation of ice

NEMA 3S

outdoors

·    falling dirt, windblown dust

·    rain, sleet , snow

·    solid ice (external mechanism remains operable)

NEMA 4

indoors/outdoors

·    falling dirt, windblown dust

·    rain, sleet, snow

·    splashing water, hose-directed water

NEMA 4X

indoors/outdoors

·    falling dirt, windblown dust

·    rain, sleet, snow

·    splashing water, hose-directed water

·    corrosion

·    damage from external formation of ice

NEMA 5

primarily indoors

·    falling dirt, settling airborne dust, lint, fibers

·    dripping and light splashing water

NEMA 6

indoors/outdoors

·    falling dirt

·    hose-directed water

·    temporary submersion at limited depth

·    damage from external formation of ice

NEMA 7

indoors 

·    internal explosions as by UL Class I, Groups C & D explosion-proof requirements

NEMA 8

indoors/outdoors 

·    combustion as per by UL Class I, Groups C & D explosion-proof requirements

NEMA 9

indoors

·    dust ignition as per UL Class II, Groups E, F, G requirements

NEMA 10

indoors/outdoors

·    internal explosions as per MSHA standards

NEMA 11

indoors

·    dripping corrosive liquids, corrosive gases

NEMA 12

indoors

·    falling dirt, circulating dust, lint, fibers

·    dripping and light splashing water

NEMA 13

indoors

·    falling dirt, circulating dust, lint, fibers

·    dripping and light splashing water

·    spraying, splashing, and seeping oil

·    non-corrosive coolants

red = hazardous conditions

What Are IP Ratings?

IP (Ingress Protection) ratings, based on the IEC 60529international standard, use a two-digit system. The first digit denotes protection against various solid intrusions, ranging from 0 (no protection at all) to 6. The second digit denotes protection against various liquid intrusions and uses a similar ranking, but going to 9K. As an example, most umbrellas are IP01: 0 = no protection against solids, and 1 = protection against water drops falling vertically.

IP is the preferred coding system in the European Union, but it is increasingly used in the U.S. and other countries as well. This table lists the IP rating codes and their general allowable conditions:

IP RATING CODES

FIRST DIGIT: PROTECTION AGAINST SOLIDS

SECOND DIGIT: PROTECTION AGAINST LIQUIDS

0

no protection

0

no protection

1

object > 50 mm (2″)

e.g., hands, larger animals

1

water drops, falling from vertical

2

object > 12 mm (.5″)

e.g., fingers, smaller animals

2

water sprays, 15° from vertical

3

object > 2.5 mm (.01″)

e.g., thick wires, tools, insects

3

water sprays, < 60° from the vertical

4

object > 1 mm (0.04″)

e.g., thin wires

4

water drops and sprays, any direction

limited ingress permitted

5

dust resistant

limited ingress permitted

5

water jets and sprays, low pressure

limited ingress permitted

6

dust proof

6

water jets, high pressure

e.g., strong jets, waves, heavy seas

 

 

7

immersion in water, limited duration

as per stated pressure and time conditions

 

 

8

immersion in water, indefinite duration

under specified pressures

 

 

9K

steam jet, high temperature and high pressure

K = as per ISO 20653

 The following are some items and their IP ratings:

  • Chain-link fence: IP10
  • Chicken wire: IP20    
  • Window screen: IP30    
  • Kevlar cloth: IP40    
  • Camping tent: IP42    
  • Plastic wrap: IP51    
  • Wine bottle: IP67    
  • Latest generations of smartphones: IP68
  • WIKA’s MH-4 pressure sensor: up to IP69K

WIKA USA offers a wide range of pressure measuring instruments that meet the specific protection requirements defined by the two classification rating system. For more information about NEMA ratings, IP codes, our IP68 and IP69K pressure transmitters, and what enclosure types or ingress protection your application needs, contact our pressure specialists.

Product mentioned in this article:

Model MH-4 OEM pressure sensor



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