ECN Forum Forums General Topics of the Trade General Discussion Area transfer switch and sub panel

I have a 200 amp main breaker panel and I am installing a 200 amp auto transfer switch. The SEU cable comes out of the panel and feeds into the transfer switch first the to the main panel. My question is if the transfer switch is hit first does that make the main panel a sub panel. Basically should I treat the transfer switch the same as a service disconnect. If it is a sub I would have to seperate the grounds and the neutrals and feed the main panel with SER cable.