When you’re installing a generator transfer switch — especially one outside your home or business — it’s important to make sure the equipment is protected from the weather, dust, and other hazards. That’s where NEMA ratings come in.
NEMA stands for the National Electrical Manufacturers Association, and they created a system to rate how well enclosures (the box around electrical parts) protect against things like rain, snow, and corrosion.
So when you’re buying or replacing an automatic transfer switch (ATS), the NEMA rating tells you where it can safely be installed — indoors, outdoors, or in rough environments.
Common NEMA Enclosure Types for ATS Installations
🔹 NEMA 1 – Indoor Use Only
This is the most basic type. It protects the internal parts from dust and accidental contact but isn’t sealed tight.
Where it’s used: Indoors only, like in a garage, utility room, or electrical closet.
🔹 NEMA 3R – Basic Outdoor Protection
This type is made for outdoor use and protects against falling rain, snow, and ice buildup. It has ventilation but isn’t sealed against hose water or windblown dust.
Where it’s used: Outside homes or businesses in moderate conditions. It’s very common for residential generator ATS installations.
🔹 NEMA 4 – Sealed Against the Elements
This enclosure keeps out rain, windblown dust, and water sprayed from hoses. It also handles snow and ice without problems.
Where it’s used: Outside in harsher environments, like commercial sites where the equipment might be sprayed down or exposed to more weather.
🔹 NEMA 4X – For Coastal or Corrosive Environments
This is just like NEMA 4 but made from stainless steel or other corrosion-resistant materials. It protects against salt air, harsh chemicals, and rust.
Where it’s used: Coastal areas near the ocean or in industrial environments where corrosion is a concern.
What Should You Use?
- For most homes, a NEMA 3R enclosure is enough. It’s rated for rain and snow and works well for most weather in Oregon and Washington.
- For commercial buildings or places with pressure washing or dust, NEMA 4 might be a safer bet.
- If your home or facility is near the coast, a NEMA 4X will give you long-term protection from rust and salt exposure.
Final Tip
When you’re choosing or upgrading your ATS, don’t just think about amps and voltage — make sure you’re getting the right enclosure for your environment. It’s the difference between long-lasting protection or expensive water damage.
Need help choosing the right NEMA rating for your next generator project? Contact Power Systems Plus — we’ve been serving Oregon homes and businesses for over 27 years.