What is the NEMA symbol for a normally open flow switch?

The NEMA symbol for a normally open flow switch is represented with a graphic that depicts an internal switch. This symbol effectively conveys the operational state of the switch when no flow is detected; it remains open and does not allow current to pass through. The internal switch graphic provides a clear visual indication that the device is in an "off" condition until the flow sensor detects the requisite fluid movement, at which point the switch closes, completing the circuit. This representation is crucial for electricians and engineers in understanding and interpreting schematics, ensuring accurate installation and functionality of these devices in a circuit.

The other options do not appropriately represent the function of a normally open flow switch. A specific graphic symbol or a circle may refer to various devices but lacks the specific characteristics of an internal switch for flow applications. A crosshatch pattern typically indicates different types of electrical components or limitations in drawings, which doesn't apply here. Hence, the internal switch graphic is the most informative and accurate symbol for this specific type of switch in NEMA standards.