Most RVs use standard automotive blade fuses for their 12-volt DC systems, with ATC (also called ATO) being the most common format you’ll encounter. These are the same small, color-coded plastic fuses found in cars and trucks, rated up to 32 volts DC and available in amperages from 1 to 40 amps. Knowing which type and size your RV uses makes replacing a blown fuse a five-minute job instead of a frustrating guessing game.
Blade Fuses: The Standard in Modern RVs
If your RV was built in the last 20 to 30 years, its 12-volt fuse panel almost certainly uses blade fuses. These come in four main sizes, and your RV may use more than one:
- Regular (ATC/ATO): The most common size, roughly 3/4 inch wide. Available from 1 to 40 amps. This is the default fuse in most RV fuse panels, protecting circuits for lights, water pumps, slide-outs, and other 12-volt accessories.
- Mini (ATM): About two-thirds the size of a regular blade fuse. Available from 2 to 40 amps. Some newer RVs and certain fuse blocks use these to save space.
- Micro: The smallest blade fuse, found in some newer electronic components. Available from 5 to 30 amps.
- Maxi: A larger, heavier-duty blade fuse for high-draw circuits. Available from 20 to 120 amps. These typically protect major systems like the power converter or a high-output inverter.
The critical thing to know: these sizes are not interchangeable. A mini fuse won’t fit in a regular fuse slot, and vice versa. Before buying replacements, pull one fuse from your panel and bring it to the store, or check your owner’s manual for the specific format.
ATC vs. ATO: A Small Difference That Matters
You’ll see ATC and ATO fuses sold side by side, and they look nearly identical. Both are regular-size blade fuses with the same amperage ratings and the same blade spacing, so they fit the same fuse holders. The difference is in how the fuse element is enclosed.
ATC fuses have a fully closed plastic housing that seals the metal element inside. ATO fuses are open at the bottom, leaving the element exposed. In an RV, where fuse panels can sit in compartments exposed to humidity, condensation, or the occasional leak, that open bottom invites corrosion over time. ATC fuses are the better choice for RV use. They cost the same, so there’s no reason to choose ATO unless it’s all you can find in a pinch.
Color Codes Tell You the Amperage
Every blade fuse is color-coded by amperage, and this system is universal across all four sizes. The amperage is also printed on the top of the fuse, but the color lets you spot a mismatch at a glance. The ratings you’ll encounter most often in an RV fuse panel:
- Tan/Beige: 5 amps
- Brown: 7.5 amps
- Red: 10 amps
- Blue: 15 amps
- Yellow: 20 amps
- Green: 30 amps
Less common in RV panels but still worth knowing: violet is 3 amps, pink is 4 amps, and transparent is 25 amps. For maxi fuses, the color coding shifts at higher amperages. A 50-amp maxi is red, 60-amp is blue, and 70-amp is amber.
When you pull a blown fuse, match the replacement to both the color and the printed amperage. Never substitute a higher-amp fuse to “fix” repeated blowing. The fuse is sized to protect specific wiring, and oversizing it can cause an electrical fire.
Glass Tube Fuses in Older RVs
RVs from the 1980s and earlier often use glass tube fuses instead of blade fuses. These are small glass cylinders with metal caps on each end, and they come in two sizing systems that look similar but aren’t always interchangeable.
The AG (Automotive Glass) system includes several sizes that vary in both length and diameter. The most common are 3AG fuses, which measure 1-1/4 inches long and 1/4 inch in diameter. You’ll also find 5AG fuses (1-1/2 inches long, 13/32 inch diameter) in some older panels. The SFE system uses a consistent 1/4-inch diameter, but the length changes with the amperage rating. A 4-amp SFE fuse is just 5/8 inch long, while a 30-amp version stretches to nearly 1-1/2 inches. This length variation is intentional: it prevents you from physically fitting the wrong amperage into a fuse holder.
If your RV still uses glass tube fuses, replacements are available at most auto parts stores. Some owners upgrade older fuse panels to blade-style fuse blocks, which makes finding replacements easier and gives you the color-coding system for quick identification.
Finding Your RV’s Fuse Panels
Most RVs have at least two fuse locations, and some have three or four. The main 12-volt fuse panel is typically near the power converter, which is the unit that converts shore power to 12-volt DC for your RV’s lighting and accessories. In travel trailers, this is often inside a lower cabinet or behind a panel near the front of the trailer. In motorhomes, it’s commonly beneath or behind a cabinet in the living area, though the chassis (engine-side) fuses sit under the dashboard or hood just like in any truck.
Some RVs also have a secondary fuse block near the battery compartment, especially for high-draw circuits. Check your owner’s manual for a diagram showing all fuse locations. If you don’t have the manual, the manufacturer’s website or an RV-specific forum for your model can usually point you to the right spot.
Many modern RV fuse panels include LED indicator lights next to each fuse position. The convention varies by manufacturer. On some panels, a red light turns on when the fuse blows. On others, the red light stays lit when the fuse is good and goes dark when it fails. Check your panel’s labeling to know which system yours uses before assuming a lit indicator means trouble.
Replacing a Blown Fuse Safely
Swapping a fuse takes seconds, but doing it safely requires a couple of extra steps. Before pulling any fuse, disconnect all power sources. Unplug your shore power cord. Turn off the generator if it’s running. Use the battery disconnect switch or remove the negative battery cable so no current is flowing through the 12-volt system.
Pull the blown fuse straight out. Most RV fuse panels include a small plastic fuse puller tool clipped to the panel cover. Look at the fuse element inside the clear plastic housing: a blown fuse has a visibly broken or melted metal strip. Replace it with a fuse of the exact same amperage and type, press it firmly into the slot, then restore power.
If the new fuse blows immediately after you reconnect power, the fuse isn’t the problem. Something downstream on that circuit is drawing too much current or has a short. That’s a sign to stop replacing fuses and have the wiring inspected by a qualified RV technician. Repeatedly forcing in new fuses when there’s an underlying short is how electrical fires start.
Keeping Spare Fuses on Hand
A small assortment of spare fuses belongs in every RV’s toolkit. You can buy multi-pack blade fuse kits for a few dollars that include the most common amperages. Grab one that matches your fuse format (regular, mini, or both if your RV uses a mix), and keep it in a dry spot near the fuse panel. If your RV uses glass tube fuses, buy a few spares in each amperage your panel requires, since convenience stores and gas stations rarely stock them. Having the right fuse on hand at 10 p.m. in a campground, when your water pump suddenly stops working, is worth far more than the couple of dollars the kit costs.