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Two thermal switches (Thermal Cut) Schematic symbol for a thermal overload switch. A thermal switch (sometimes thermal reset or thermal cutout (TCO)) is a device which normally opens at a high temperature (often with a faint "plink" sound) and re-closes when the temperature drops. The thermal switch may be a bimetallic strip, often encased in a ...
5. Electrical devices are shown in their normal conditions. An NC contact would be shown as normally closed, and an NO contact would appear as a normally open device. All contacts associated with a device will change state when the device is energized. Figure 1 shows a typical relay logic diagram.
External Device Monitor (EDM). The device issuing the OSSD signals may have an EDM input. The EDM is used to verify that the controlled device (safety relay) did indeed open when the OSSD signals were dropped. The safety relay has normally closed contacts, which close when the relay is de-energized, thereby turning on the EDM input.
Time-delay relay contacts must be specified not only as either normally open or normally closed, but whether the delay operates in the direction of closing or in the direction of opening. The following is a description of the four basic types of time-delay relay contacts. First, we have the normally open, timed-closed (NOTC) contact.
Each key of a computer keyboard, for example, is a normally-open "push-to-make" switch. A "push-to-break" (or normally-closed or NC) switch, on the other hand, breaks contact when the button is pressed and makes contact when it is released. An example of a push-to-break switch is a button used to release a door held closed by an electromagnet.
The National Association of Relay Manufacturers and its successor, the Relay and Switch Industry Association define 23 distinct forms of electrical contact found in relays and switches. [12] A normally closed (NC) contact pair is closed (in a conductive state) when it, or the device operating it, is in a deenergized state or relaxed state.
power engineering That part of electrical engineering that deals with the generation, distribution and consumption of electrical power. power-factor correction Apparatus intended to bring the power factor of some load closer to 1. power factor The ratio of apparent power flowing to a load divided by the real power. power-flow study
A smaller unit which simulates a complete unit or element in an electrical test, without reducing the severity of the electrical, thermal or mechanical conditions. [v] multi-connected converter A converter consisting of two or more converter units parallel connected or series connected or both, each of which is an operative converter of its own.