Before installing a major appliance like a hot tub, determine if the electric service will handle the extra load. It's usually not a problem, since most homes built in the last 30-40 years have at least a 100 amp service, with a 200A service common in newer homes. Panel ratings are normally labeled near the main breaker at the top.
 

It's a common misconception that the sum total of the amps of all the circuit breakers installed must not exceed the service panel's indicated amp rating. This is false-- capacity is determined by load calculations, not the size or number of its breakers.
Spa Wiring Basics - 240V Systems

We'll begin with an overview of the electrical requirements for wiring a hot tub, as illustrated by our interactive wiring diagrams below. A 240V spa must be supplied by a circuit which meets its load requirements (amperage) as indicated in owner's manual.

This means that the feeder breaker (in the house service panel) must be of the specified size, and that the GFCI breaker in the disconnect panel must be at least that size (larger is fine) and is GFCI protected for safety.

We're using a typical outdoor portable home spa installation for our example.
The three electrical assemblies involved in this project are the:

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