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Networking & ProtocolsReviewed 2026-08-28

NO vs NC

normally open (NO) is open until it activates. normally closed (NC) is closed until it activates.

N.O.open at restN.C.closed at rest

Safety and fire circuits often need normally closed (NC). Operators often want normally open (NO).

Match the input the operator or panel lists.

Also called
NO vs NCnormally open contactnormally closed contactNormally open vs normally closednormally open vs normally closed contacts
Catalog fields
Output TypeContact Rating

Source: Transmitter Solutions product training