What is a relay in a box
A relay in a box is a type of electrical switch that can be plugged into an outlet and operated with a handheld, remote-controlled power switch. The advantages of the relay in a box are that it is easy to install and provides an electricity disconnect (breaker) for safety. A basic relay in a box is shown in Fig. 2.
Figure 2.A Typical Relay in the Box.
A relay in the box can be used to control a switch or an outlet. The relay is hardwired to a standard electrical circuit consisting of a fuse and circuit breaker. When the existing switch or outlet is in use, the relay receives power by means of a cord that plugs into the electrical outlet, as shown in Fig. 3.. When turned on, it activates the breaker and provides power to whatever device is connected to the device contacts on its faceplate. When the device is “off”, the relay provides a path for electricity to flow to ground, disconnecting the device from the power supply. If a breaker is used, it will trip and reset when the relay receives too much current or voltage. This protects both the electrical system and devices connected to it.
Figure 3.A Relay in a Box as an Outlet Switch (No Breaker).
How does it work
To operate the relay in a box, a lefthanded person presses the “on” button, causing current to flow from the source to the load. The current is conducted by one of two leads or blades. These are connected through a common circuit and switch contact. A current-limiting voltage is applied to the circuit. The switch contact makes a trip (or break) on the load, causing current to stop flowing through the circuit with no voltage across the contacts of the relay. This can be done by pressing and holding down a button or pulling up a lever attached to one of two blades that are connected across the common circuit. The other blade engages the contacts in a different position than the button or lever is held down. When the button or lever is released, an electromotive force develops across the second load and is used to operate a motor or other device.
To operate a relay in its off state, you press and hold an on-off switch or push a button. When the switch or button is released, it causes current to flow through the relay’s mechanism to trip its switch contacts. To operate the relay in an on state, an electromotive force must be applied to move the switch contacts out of their original position. The electromotive force can be from a supply voltage (with a potentiometer or rheostat), from another relay, or from the source (but not usually with a rheostat).
