Outlet Types Explained (15A, 20A, TR, WR)

The letters and numbers stamped on a receptacle face aren't decoration; each one identifies a specific rating or safety feature the NEC requires in particular locations. A 15A and a 20A outlet look almost identical but aren't interchangeable on every circuit, and TR and WR markings indicate protection features that are now mandatory in most homes, not optional upgrades. Getting the wrong type in the wrong place is one of the more common reasons a rough-in or final inspection gets flagged. This guide explains what each marking means, where code requires it, and how to tell which type is already installed.

15A vs. 20A Receptacles

The amperage rating refers to how much current the receptacle itself is rated to handle safely, which has to match the circuit's breaker and wire size, not be chosen independently. A 15-amp receptacle has two straight vertical slots; a 20-amp receptacle has one straight slot and one T-shaped slot, which allows it to accept both a standard 15-amp plug and a 20-amp plug with the sideways prong that matches the T-shaped slot. This is a one-way compatibility: a 15-amp receptacle cannot accept a true 20-amp plug, but a 20-amp receptacle accepts both plug types.

A receptacle's amperage rating must match its circuit; installing a 20-amp receptacle on a 15-amp circuit wired with 14 AWG wire is a code violation, since the receptacle would allow a 20-amp plug to draw more current than the circuit's wire and breaker are rated to carry safely.

TR: Tamper-Resistant Receptacles

Tamper-resistant (TR) receptacles have spring-loaded internal shutters that only open when equal pressure is applied to both slots simultaneously, the way a real plug's two prongs press in together. A single object, like a child pushing a paperclip or key into just one slot, can't trigger the shutters to open. NEC 406.12 requires listed TR receptacles for all 15A and 20A, 125V and 250V nonlocking-type receptacles in dwelling units, including attached garages and accessory buildings, plus a range of non-dwelling locations such as hotel guest rooms, child care facilities, and medical and dental office waiting areas. This has been a standard NEC requirement since the 2008 code cycle and applies to new installations and replacements alike in covered locations.

WR: Weather-Resistant Receptacles

Weather-resistant (WR) receptacles are built with additional corrosion resistance, UV-resistant materials, and tighter internal tolerances to withstand damp and wet locations without degrading over time. NEC 406.9 requires nonlocking 15A and 20A receptacles installed in wet or damp locations to be listed WR, and a WR receptacle installed outdoors or in a damp area still needs the correct in-use, weatherproof cover appropriate for the location, since the WR listing covers the receptacle itself, not the enclosure around it. Many current outdoor and TR receptacles combine both features into one device, marked with both TR and WR on the face.

How Wet vs. Damp Locations Differ

Code distinguishes between damp and wet locations, and the enclosure requirement differs accordingly. A damp location, such as under a roofed open porch or canopy not exposed to direct rain or runoff, requires a WR receptacle in an enclosure that's weatherproof when no plug is inserted. A true wet location, exposed to direct weather, requires a WR receptacle in an enclosure that stays weatherproof even with a cord plugged in, using an "extra duty" rated, in-use cover. Choosing the enclosure based on actual exposure rather than defaulting to the minimum matters for long-term reliability, not just passing inspection.

GFCI: A Separate but Related Requirement

GFCI protection is a different requirement layered on top of, not instead of, the TR and WR rules. NEC 210.8 requires GFCI protection in bathrooms, garages, outdoor locations, kitchens, laundry areas, unfinished basements, and several other locations, and a GFCI receptacle installed outdoors still needs to carry the WR listing on top of its GFCI function, and still needs TR shutters where TR applies. A single device can, and in many locations must, satisfy all three requirements at once.

Where Each Requirement Applies at a Glance

How to Tell What's Already Installed

• Check the face of the receptacle for "TR" or "WR" markings, usually stamped near the top or bottom edge.
• Check the slot shape: a T-shaped slot indicates a 20-amp receptacle.
• For outdoor receptacles, check whether the cover is a simple flip-lid (damp-rated) or a bubble-style "in-use" cover (wet-rated, extra duty).
• When replacing an existing receptacle, match or upgrade to current requirements rather than simply replacing like-for-like, since older installations may predate current TR and WR rules.

The Bottom Line

The markings on a receptacle face tell a specific, code-driven story: amperage rating and slot shape (15A vs. 20A) have to match the circuit, TR shutters are now required in nearly every dwelling-unit location to protect against a very specific childhood injury pattern, and WR construction is required anywhere a receptacle faces damp or wet exposure. GFCI protection layers on top of all of this in kitchens, bathrooms, garages, and outdoor locations, and a single receptacle in the right spot may need to carry all three markings at once. Checking these markings against the location's actual requirements, rather than assuming an existing installation is already compliant, is the fastest way to catch a gap before an inspector does.