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Most relay coils don't care which end gets power or ground but ones with diodes do so make a habit of using 86 as the coil power in and 85 as ground. Either and/or both side(s) may be switched. Terminal 30 is common, meaning that it can contact either 87 or 87a (if a SPDT relay). When the relay is in its neutral state, normally closed (NC) indicates a completed circuit with 30 (as in 87a); normally open (NO) indicates an open circuit (as in 87).