The Transfer Safety Switch -- An Essential Element

Typically, the transfer switch is located between the utility meter and the loads to be served. It should be within 25 feet or less of the generating unit for convenience and safety. If the location of critical loads are scattered among several outbuildings, the central meter pole may be the best location for both the transfer switch and the generator.

The size of the transfer switch is determined by the loads to be served. If a central meter pole location is used, the transfer switch rating must be equal to the size of the main service (typically 100, 200 or 400 amperes). If the standby system is designed to supply an individual building, or even a single circuit, the transfer switch will be sized to the total ampere rating of the connected loads.

If an engine-driven generator with automatic start-up is used, the transfer switch is normally built into the automatic controls of the system. In this case, the transfer switch must be large enough to handle all electrical loads, size the switch to match the rating of conductors which supply regular power to the building(s) or farmstead.

Adding a standby generator to the electrical system of a home, farm or business requires a suitable transfer safety switch to disconnect the electric loads from the power suppliers utility grid. This is a requirement of the National Electrical Code (NEC Article 702-6) and all electric power suppliers, for three very good reasons:

1. If an emergency generator is connected directly to the house or farm electrical system without the isolation provided by a transfer safety switch, electric power can travel back through the utility service wires and onto the utility power lines. The 240 volts produced by the emergency generator will be boosted by the utility transformer to the distribution voltage level (e.g.,4800,7200, or 12,000 volts or more). Unsuspecting linemen working on a supposedly dead power line can be killed or seriously injured.
   
   
2. If the power produced by your generator is allowed to access the utility power line, your generator may energize a neighbor's electrical system and attempt to pick up any electrical load that may not be switched off. This could seriously overload and damage the emergency generator.
   
   
3. Finally, without isolation from the utility power line, an operating emergency generator can be severely damaged or destroyed when the utility power comes back on. The utility power will be out of phase (not synchronized) with the generator and will cause the generator windings to be burned up.It prevents the back flow of current into the utility's lines during an outage, which could electrocute linemen working to restore power.

Click here for proper Double-Throw or Transfer Safety Switch installation.