· by Michael Blair, Nashville's Electrician
Middle Tennessee loses power to spring storm lines, summer thunderstorms and the occasional ice event, and outages here are measured in hours to days rather than minutes. The question is rarely which generator. It is how it connects to the house, and that is where the code, the safety and most of the cost live.
Why backfeeding is the thing that kills people
Running a cord from a generator into a dryer or range outlet to energize the house is called backfeeding, and it is illegal everywhere for a reason. Power flows back through the panel to the utility transformer, which steps it up to distribution voltage on the line outside.
That puts thousands of volts on wires that a lineman has already tested and grounded. It also means that when utility power returns, it meets your generator output, which destroys the generator and can start a fire. There is no version of this that is acceptable.
What a transfer switch actually does
A transfer switch makes it physically impossible for the generator and the utility to be connected at the same time. That is its entire job and it is not optional. It is what turns a generator from a hazard into an appliance.
A manual transfer switch with a set of circuits, or an interlock kit that mechanically prevents the main breaker and the generator breaker being on together, covers a portable generator at modest cost. An automatic transfer switch senses the outage, starts a standby generator and switches over without anyone being home.
- Interlock kit: cheapest compliant option for a portable unit
- Manual transfer switch: selected circuits, switched by hand
- Automatic transfer switch: pairs with a standby generator, unattended
- All three require a permit and an inspection
- None of them are a substitute for correct generator grounding
Portable or standby, and how to choose
A portable generator with an inlet box and an interlock covers the essentials: the refrigerator, the furnace blower, some lights and outlets, and the well pump if you have one. It needs someone home to roll it out, start it and refuel it every several hours, and it has to run outdoors well away from windows.
A standby unit runs on natural gas or propane, starts itself, and carries either the whole house or a defined set of circuits. It costs several times as much installed and it needs a gas line and a concrete pad. The case for it is a household that cannot go without power, or a house nobody is at during storm season.
Sizing, and the two loads people forget
Sizing is about starting loads rather than running loads. Anything with a motor draws several times its running current for a moment as it starts, and an air conditioner compressor or a well pump starting is what stalls an undersized generator.
The two that get forgotten in Middle Tennessee are the furnace blower and the sump pump. A gas furnace still needs electricity to run the blower and the controls, and a house with a wet crawl space that loses its sump during a storm has traded a power outage for a water problem.