Check the terminals of the coil for polarity when applicable, especially in DC circuits. Typically, these are depicted as a set of three or four pins: normally open (NO), normally closed (NC), and a. The numbers 30, 85, 86, and 87 represent a standardized terminal numbering system defined by the DIN 72552 standard, originally developed for automotive applications but now widely adopted in various industrial settings. These terminal designations create a universal language for relay connections. Any industrial electrician can instantly recognize a relay, but when it comes to wiring, why are the terminals numbered in such apparently random order? Wiring relays can be a difficult challenge even for experienced electricians. The widely used United Sates standard ANSI/IEEE C37. 2 'Electrical Power System Device Function Numbers, Acronyms, and Contact Designations' deals with protective device function numbering and acronyms. Even in those parts of the world where IEC standards are predominate, the use of ANSI numbering. The protection and control devices in electrical equipment can be referred to by numbers, with appropriate suffix letters when necessary, according to the functions they perform.