Off Delay: Off delay signifies that the timing period of a time delay relay is initiated upon de-energizing of its coil.

Offset: The steady state deviation of a controlled variable from a fixed setpoint.

Oil Mist Lubrication: A centralized lubricating system in which the energy of compressed gas, usually air taken from the plant supply, is used to atomize oil. Oil is then conveyed by the air in a low pressure distribution system to multiple point of lubricant application.

On Delay: On delay signifies that the timing period of a time delay relay is initiated upon energization of its coil.

Open Circuit: An open circuit in a motor is a defect which causes an interruption in the path through which the electric current normally flows.

Open Loop: A control system that lacks feedback.

Operating Overload: Operating overload is the overcurrent to which an electric apparatus is subjected in the course of the normal operating conditions that it may encounter. For example, those currents in excess of running current which occur for a short time as a motor is started or jogged are considered normal operating overloads for a control apparatus.

Op Amp: An operational amplifier is usually a high gain DC amplifier that is designed to be used with external circuit elements to perform a specified computing operation.

Open Machine (Motors): A machine having ventilating openings which permit passage of external cooling air over and around the windings of the machine.

1. Drip-proof Machine - is an open type machine in which the ventilating openings are so constructed that successful operations is not interfered with when drops of liquid or solid particles strike or enter the enclosure at any angle from 0 to 15 degrees downward from vertical.
2. Splash-proof - is an open machine in which the ventilating openings are so constructed that successful operation is not interfered with when drops of liquid or solid particles strike or enter the enclosure at any angle not greater than 100 degrees downward from the vertical.
3. Semiguarded - is an open machine in which part of the ventilating openings in the machine, normally in the top half, are guarded as in the case of a "guarded machine," while the other parts are left open.
4. Guarded Machine (NEMA Standard) - is an open machine in which all openings giving direct access to live metal or rotating parts (except smooth rotating surfaces) are limited in size by the structural parts or by the screens, baffles, grilles, expanded metal or other means to prevent accidental contact with hazardous parts. Openings giving direct access to such live or rotating parts shall not permit the passage of a cylindrical rod 0.75 inch in diameter.
5. Drip-proof Guarded Machine - is a drip-proof machine whose ventilating openings are guarded in accordance with the definition of a guarded machine.
6. Open Externally Ventilated Machine - is one which is ventilated by means of a separate motor driven blower mounted on the machine enclosure. This machine is sometimes known as a blower-ventilated or a force-ventilated machine.
7. Open Pipe Ventilated Machine - is basically an open machine except that openings for admission of ventilating air so arranged that inlet ducts or pipes can be connected to them. Air may be circulated by means integral with the machine or by means external to the machine (separately or forced ventilated).
8. Weather Protected Machine - is an open enclosure divided into two types:

1. Type 1 enclosures have ventilating passages constructed to minimize the entrance of rain, snow, airborne particles and prevent passage of a 0.75 in. diameter cylindrical rod.
2. Type 2 enclosures provide additional protection through the design of their intake and exhaust ventilating passages. The passages are so arranged that wind and airborne particles blown into the machine can be discharged without entering directly into the electrical parts of the machine. Additional baffling is provided to minimize the possibility of moisture or dirt being carried inside the machine.

Operating Service Deviation: A means of specifying the speed regulating performance of a drive's a controller, generally in percent of base speed.

Operating Deviation defines speed change due to load change and typically assumes:

1. A change from one steady state load value to another (not transient).
2. A 95% maximum load change.

Service Deviation defines speed change due to changes in ambient conditions greater than these typical variations:

Output Torque, Gear: A calculation of the input torque multiplied by the gear ratio and the gear efficiency.

Overcurrent Relay: An overcurrent relay operates when the current through the relay, during its operating period, is equal to or greater than its setting.

Overhung Load: A load which tends to impose a radial force (perpendicular to the shaft axis) on a motor or gear-motor output shaft.

Overshoot: The amount that a controlled variable exceeds a desired value after a change of input.

Overspeed: Any speed above the rated (nameplate) speed. Can be caused by a load overhauling (crane and elevator motors), or intentional as on induction generators.

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