AUTOMATIC TRANSFER SWITCH |
When connecting the generator to a building electrical distribution system, use of a transfer switch is recommended to isolate the normal utility source from the generator supply. By preventing backfeed of the generator power into the utility lines during a utility power outage, the switch provides a level of safety for electrical line workers. An automatic transfer switch listed to Underwriters Laboratories Standard 1008 performs this function while also supplying a method to automatically start and stop the generator set and transfer power to the building electrical system from an appropriate source.
When planning for a transfer switch/generator installation, it is necessary to know the method of interconnection to the building system. As illustrated, it is recommended to connect the generator to power only circuits that are necessary during a power outage. When following this method, the transfer switch feeds an electrical
Figure 1
Example of Recommended Transfer
Switch Installation
(Essential
A
B
C 
D E
AUtility Power
BStandby Generator
CMain Circuit Panel
DAutomatic Transfer Switch
EEssential Loads
Figure 2
Example of Alternative Transfer
Switch Installation
(Main Panel Load)
A
B
C
D
AUtility Power
BStandby Generator
CMain Circuit Panel
DAutomatic Transfer Switch
Switch selection is based on factors such as the size of the building distribution system, available generator power and required generator control system. Due to the complex nature of electrical distribution systems, the sizing, selection and installation of a switch is best handled by a licensed electrician or qualified standby generator dealer. Any switch installation must be performed by a licensed electrician to the instructions of the switch manufacturer and any applicable local, regional or national codes.
WARNING
•Hazardous "backfeed" voltage can cause severe injury or death. Install a transfer switch in standby power installations to prevent connection of standby to other sources of power. Electrical backfeed into a utility electrical system can cause serious injury or death to utility personnel working on transmission lines.
•Do not try MANUAL operation of the transfer switch until all power supplied to the switch has been positively turned OFF. Failure to remove power from all sources may result in extremely dangerous and possibly lethal electrical shock or arching.
7 |