Sometimes. Optional standby systems in the National Electrical Code (Article 702 in current editions) require transfer equipment that prevents interconnection with the utility. A listed interlock kit, used on the panel it is listed for, is a common way electricians meet that idea in a manual, whole-panel arrangement: the main and the generator breaker cannot be on together. Whether your inspector treats a particular kit as acceptable transfer equipment is a local decision. A homemade interlock, a kit on the wrong panel, or a dryer-outlet backfeed is not a substitute.
This is why the listing matters as much as the physics of the sliding plate. The kit has to be identified for the panel, installed so it actually forces the correct breaker sequence, and paired with a proper inlet — not a cord through a window. Some jurisdictions prefer a separate transfer switch; some accept interlocks routinely. Ask before you buy the hardware.
An interlock is still manual. It does not become an automatic transfer switch by meeting code. See the interlock-versus-transfer-switch page, pull a permit (see that page), and size loads with the calculator.
This is not a permit calculation, a utility approval, or a substitute for a licensed electrician, HVAC contractor, or the authority having jurisdiction. Panel Headroom is an independent educational site. It is not a utility, a certification body, or a contractor. Electrical and generator work that is done incorrectly can cause fire, shock, or carbon monoxide poisoning. Use the adopted electrical code and manufacturer instructions; pull permits where required.