Specialty · Franklin County & St. Louis, MO
A transfer switch is the code-required piece that lets a generator safely power your home without back-feeding the utility line. CAS Electric installs manual (interlock and rotary) and automatic transfer switches across Franklin County and the Greater St. Louis area — Pacific, Washington, Union, Sullivan, St. Clair, Eureka, Wildwood, Villa Ridge, and Marthasville. This page breaks down real installed costs, the differences between manual and automatic switches, permit requirements, and what to expect on install day.
A generator transfer switch is what makes generator power legal, safe, and code-compliant. Plugging a portable generator into a wall outlet — or running extension cords through a window — is not just unsafe, it can back-feed the utility line and electrocute a lineman working to restore power. A transfer switch physically isolates your home's circuits from the utility before generator power is applied, so only one power source is ever connected at a time.
There are three common styles in Franklin County and St. Louis homes. A generator interlock kit is the most affordable — a mechanical plate installed on your existing panel that blocks the main breaker and a generator inlet breaker from being on at the same time. A manual transfer switch is a separate small sub-panel with 6–10 selectable circuits you flip over during an outage. An automatic transfer switch (ATS) senses utility loss, starts a standby generator, and transfers the load in about 10 seconds — no one has to be home.
Installed cost depends on the switch type, amperage, whether a critical-loads sub-panel is added, and how far the generator inlet or generator itself sits from the panel. We give a flat written quote up front. CAS Electric pulls the electrical permit, coordinates with Ameren when a disconnect is required, and commissions the switch with a simulated outage before we leave.
Transfer switch pricing depends on the switch type (interlock kit, manual, or automatic), amperage, distance from the panel, and whether a critical-loads sub-panel is added. Every quote is flat and written — contact us for a free estimate. No hourly billing.
We look at your panel, generator (or planned generator), and inlet location, then give you a flat written price with the switch type and installed cost broken out.
We pull the electrical permit, coordinate Ameren if a service disconnect is needed, and schedule the install at your convenience.
Interlock kits and manual transfer switches are typically a same-day install. Automatic transfer switches paired with a new standby generator can take 1–2 days.
We run a simulated outage to verify the switch transfers correctly and the generator starts, stabilizes, and carries the load. Inspector signs off and you get a labeled switch and quick-start guide.
Installed cost depends on the transfer switch type (interlock kit on your existing panel, manual switch with a small critical-loads sub-panel, or automatic transfer switch), amperage, distance from the panel, and whether a critical-loads sub-panel is added. Full standby generator + ATS packages are quoted as a bundle. We provide a free written estimate scoped to your setup — no hourly billing.
A manual transfer switch (or interlock kit) requires you to be home during an outage — you shut off your main breaker and flip the transfer switch to generator power. An automatic transfer switch (ATS) is paired with a standby generator and does everything for you: it senses utility loss, starts the generator, transfers the load in about 10 seconds, and transfers back when utility power returns. Manual is cheaper up front; automatic is convenient and works when you're away.
Yes, when installed correctly and permitted. A generator interlock kit is a listed, code-compliant option that mechanically prevents your main breaker and generator inlet breaker from being on simultaneously. It's the most affordable path to safe, legal generator power for a portable unit. The trade-off vs. a manual transfer switch is that you're using your existing panel's breakers to pick which circuits run on generator power, rather than a dedicated sub-panel with pre-selected circuits.
Yes — every Franklin County and St. Louis-area jurisdiction requires an electrical permit and inspection for transfer switch installations, whether it's an interlock kit, a manual switch, or an ATS. We pull the permit, schedule the inspection, and handle Ameren coordination when a service disconnect is required.
Most generator interlock kits and manual transfer switches are a single-day install — usually 3–6 hours on site including panel work and inlet mounting. Standalone automatic transfer switches for an existing generator are typically a one-day job. A full new standby generator + ATS install runs 1–2 days on the electrical side, plus a separate visit from a licensed plumber for the gas line.
The transfer switch amperage should match (or exceed) your generator's output and your intended load. Typical portable generator setups use 30-amp or 50-amp switches. Standby generators for whole-home coverage typically pair with a 200-amp service-entrance ATS. During the estimate we look at your generator nameplate and the circuits you want covered, then size the switch accordingly.
It's not legal in Missouri to install a permanent transfer switch without a licensed electrician pulling the permit and having the work inspected. Beyond the legal side, a mis-wired transfer switch can back-feed the utility line and injure or kill a lineman, or destroy the generator when utility power returns. This is the exact scenario transfer switches exist to prevent — it needs to be done by someone licensed and inspected.
Manual transfer switches and interlock kits are generator-agnostic — they'll work with any brand of portable or inverter generator with a matching outlet (typically L14-30 or CS6375). Automatic transfer switches need to be compatible with the generator's start signal; most modern standby generators from Generac, Kohler, Briggs & Stratton, and Cummins have compatible ATS options and we'll spec accordingly.
Licensed, insured, owner-operated. We respond to all estimates within 1 business day.