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Enclosures of electrical equipment, per characteristics where they will be installed and their maintenance accessibility, should offer a certain degree of Protection also known as Ingress Protection (IP). Standard IEC 60034-5 defines the degrees of protection of electrical equipment by means of the characteristic letters IP, followed by two characteristic numerals. NEMA also defines IP ratings for enclosures. Read IEC Ingress Protection Ratings.  Read also : NEMA Ingress Protection Ratings 

The IEC and NEMA IP ratings are defined for all spectrum of equipment used in an environment where dust, particles, water etc can compromise their performance. However specifically for motors, the standards define the below listed commonly used IP ratings such that there can be no misinterpretation:

Motor	Degree of Protection	First Characteristic Numeral		Second Characteristic Numeral
		Protected Against Accidental Contact	Protected Against Solid Objects	Protected Against Water
Open Motors	IP00	Non-Protected	Non-Protected	Non-Protected
	IP02	Non-Protected	Non-Protected	Protected against dripping water even when tilted 15° vertically
	IP11	Protection against accidental contact with the hand	Ingress of solid objects exceeding 50mm in diameter	Protection against dripping water falling vertically
	IP12	Protection against accidental contact with the hand	Ingress of solid objects exceeding 50mm in diameter	Protected against dripping water even when tilted 15° vertically
	IP13	Protection against accidental contact with the hand	Ingress of solid objects exceeding 50mm in diameter	Protected against dripping water even when tilted 60° vertically
	IP21	Protection against the touching with the finger	Ingress of solid objects exceeding 12mm in diameter	Protection against dripping water falling vertically
	IP22	Protection against the touching with the finger	Ingress of solid objects exceeding 12mm in diameter	Protected against dripping water even when tilted 15° vertically
	IP23	Protection against the touching with the finger	Ingress of solid objects exceeding 12mm in diameter	Protected against dripping water even when tilted 60° vertically
Closed Motors	IP44	Protection against the touching with tools	Ingress of solid objects exceeding 1mm in diameter	Protection against splashing water from any direction
	IP54	Protection against contacts	Protection against accumulation of harmful dust	Protection against splashing water from any direction
	IP55	Protection against touches	Protection against accumulation of harmful dust	Protection against any water jets from any direction

For special and more dangerous areas where electric motors are required to be applied, the following degrees of protection are commonly used:
IPW 55 (Weather protection)
IP56 (Protections against water jets)
IP65 (Totally protected against dust)
IP66 (Totally protected against dust and water jets).