Tamper-resistant receptacles use spring-loaded shutters to block single-prong insertion — and since the NEC first required them in dwelling units, the list of locations where they are mandatory has grown with each code cycle.
A tamper-resistant (TR) receptacle contains spring-loaded plastic shutters behind each slot. When the shutters are at rest, they cover the energized contacts so that inserting a single object into one slot — a coin, a key, a hairpin — meets a physical barrier rather than a live terminal. The shutters only open when both slots receive simultaneous, equal pressure, which is what the two prongs of a standard plug provide.
The hazard being addressed is the classic childhood electrical injury: a child inserts an object into a single receptacle slot and receives a shock or burn from the energized contact. Ordinary plastic outlet caps were the traditional workaround, but they can be removed, lost, or forgotten. Because the TR mechanism is built into the device itself, the protection is always present regardless of how the receptacle is used over its life.
TR receptacles are not the same as GFCI devices. A GFCI interrupts the circuit when it detects current flowing to ground rather than returning through the neutral. A TR receptacle is a mechanical guard — it does not interrupt the circuit at all; it prevents unwanted contact from occurring in the first place. Locations that require both a GFCI and a tamper-resistant feature can be served by combination GFCI/TR devices, which are widely available and satisfy both requirements with a single device.
Section 406.12 is the governing provision. Dwelling units are the foundational required location: receptacles installed in dwelling units must be listed tamper-resistant types. The code does not limit this to receptacles in rooms children are likely to be in — it applies to receptacles throughout the dwelling, including garages, basements, and outdoor outlets.
Beyond dwelling units, the required locations have expanded in recent NEC editions. Without attributing specific changes to specific editions, the categories that have been added over time include:
When the exam names a specific edition, answer for that edition's list. When the edition is not specified, dwell on the pattern: the code has moved from dwelling units only toward any occupied space where children are likely to be present. Knowing that dwelling units have been required from the beginning, and that the expansion follows child-occupancy logic, handles most questions without memorizing year-by-year changes.
Listed tamper-resistant receptacles are required to be marked "TR" on the face of the device. That marking is mandated by the product listing standard (UL 498), not by the NEC text of 406.12 itself — what 406.12 requires is that the devices be listed tamper-resistant types. In practice, an inspector verifies compliance at rough-in or trim-out by looking for the TR marking on the face. Standard receptacles without that marking, even if they look identical, do not comply in locations where 406.12 applies.
Functionally, a TR receptacle feels stiffer to plug into because the shutters require the simultaneous pressure of both prongs to move. This is the same physical sensation for every standard plug — a correctly operating TR receptacle accepts plugs normally; the slight additional resistance is the shutters yielding to even pressure.
The NEC generally requires that where a receptacle is replaced in a location that requires tamper-resistant protection under the edition in effect, the replacement device must also be tamper-resistant. The intent is to prevent indefinite grandfathering — a receptacle that burns out or fails in a dwelling is replaced with a TR unit as a matter of course, not as an upgrade.
This same principle appears alongside AFCI and GFCI requirements: when you touch it, bring it up to current code. For the exam, the takeaway is that TR is not limited to new construction; receptacle replacements in covered locations also trigger the requirement. Knowing which locations are covered under the adopted edition, and that replacement work is included, is the full scope of what the journeyman exam tests on this topic.
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