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2. Uninterruptible power supply - Wikipedia

   en.wikipedia.org/wiki/Uninterruptible_power_supply

   A large data-center-scale UPS being installed by electricians. An uninterruptible power supply (UPS) or uninterruptible power source is a type of continual power system that provides automated backup electric power to a load when the input power source or mains power fails.

3. Doorbell - Wikipedia

   en.wikipedia.org/wiki/Doorbell

   Pressing the doorbell button, a single-pole, single-throw (SPST) pushbutton switch momentarily closes the doorbell circuit. One terminal of this button is wired to a terminal on a transformer. A doorbell transformer steps down the 120 or 240-volt AC electrical power to a lower voltage, typically 6 to 24 volts. The transformer's other terminal ...

4. Backup battery - Wikipedia

   en.wikipedia.org/wiki/Backup_battery

   A backup battery provides power to a system when the primary source of power is unavailable. Backup batteries range from small single cells to retain clock time and date in computers, up to large battery room facilities that power uninterruptible power supply systems for large data centers. Small backup batteries may be primary cells ...

5. Circuit breaker - Wikipedia

   en.wikipedia.org/wiki/Circuit_breaker

   Two-pole common-trip breakers are common on 120/240-volt systems where 240 volt loads (including major appliances or further distribution boards) span the two live wires. Three-pole common-trip breakers are typically used to supply three-phase power to powerful motors or further distribution boards.

6. Electric bell - Wikipedia

   en.wikipedia.org/wiki/Electric_bell

   Before widespread distribution of electric power, bells were necessarily powered by batteries, either wet-cell or dry-cell type. [2] Bells used in early telephone systems derived current by a magneto generator cranked by the subscriber. In residential applications, a small bell-ringing transformer is usually

7. Transfer switch - Wikipedia

   en.wikipedia.org/wiki/Transfer_switch

   When utility power returns for a minimum time, the transfer switch will transfer the house back to utility power and command the generator to turn off, after another specified amount of "cool down" time with no load on the generator. A transfer switch can be set up to provide power only to critical circuits or to entire electrical (sub)panels.