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The Reliance Controls, TTH2003DR is designed to act as a service disconnect much like the Generac 6335. The products are similar in this way as will as the fact that they can support branch circuits.
The main difference between the two products is that the TTH2003DR is rated to handle only 30 amps of power from the generator while the 6335 is rated for up to 50 amps. Also, the Reliance Controls product will require the installation of a power inlet box, while the Generac 6335 has the 50 amp connection pre-installed.