Undersizing the transfer switch or generator
A transfer switch sized to today's panel but not tomorrow's needs (like an added central AC unit) is a common, expensive-to-fix mistake. The same applies to a generator sized only for current appliances without any margin for future changes.
Skipping or delaying permits
An installer proposing to skip permitting to save time is a red flag, not a convenience — it removes independent verification that the installation is safe, and can create real problems at resale or with an insurance claim later.
Ignoring clearance requirements
Placing the generator wherever is most convenient, rather than where manufacturer clearance and local code actually allow, can mean a costly relocation later if it fails inspection.
Assuming maintenance isn't necessary
A generator is easy to forget about between outages, but skipped maintenance is one of the most common reasons a unit fails exactly when it's needed most.
Choosing based on price alone
The lowest quote isn't automatically the best value if it's achieved by excluding scope — a smaller transfer switch than the panel actually needs, no permit filing, or a generator sized without a real load calculation. Comparing quotes on identical scope, not just the bottom-line number, is what actually protects against this mistake.
Frequently asked questions
Sources
- NFPA 70 — National Electrical Code — Governs the electrical wiring and transfer switch requirements referenced throughout residential generator installation.
- Local building/electrical permitting authority — The authority having jurisdiction sets the actual permit and inspection requirements for your specific address.