The reason you need a transfer switch on the generator is to guarantee you do not run the generator and electrical power together.
If this would happen, you could damage the wiring in your home.
The generator has a switch with three settings:
(1) generator, (2) center off and (3) utility.
This setting allows the generator to kick in there is a power outage and no power is detected.
When the switch is on this setting, the information to the generator and the house is shut down.
This setting protects an electrician working on outside lines or in your home. If power was shut down, the generator would kick in and supply the house with electricity.
When the switch is in this position, the house is operating on the electric service.
This setting prevents the generator and electrical system from running at the same time.
If you have a generator, you must have a transfer switch to prevent any problems.
A professional, licensed and insured electrician can install the generator and transfer switch and instruct you on how everything works.
You should never attempt this installation yourself. One simple mistake could cause damage to your electrical wiring, serious injury to yourself, or even fire.
Rectifying a mistake can cost you more than the initial cost of having a professional electrician do the job.