Tamper Resistant Receptacles (TRR)

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Each year, approximately 2,400 children suffer severe shock and burns when they stick items into the slots of electrical receptacles – that is nearly seven children a day. It is estimated that there are six to 12 fatalities a year related to this. Nearly one-third of these injuries are the result of small children placing ordinary household objects, such as keys, pins, or paperclips into the outlets with disastrous consequences.

Located in practically every room in every house, electrical outlets and receptacles represent a constant and real danger wherever young children are found.

But now, new technology called tamper resistant receptacles, or TRRs, provide a simple, affordable, reliable, and permanent solution to help prevent these kinds of injuries.

TR receptacles are preferred over products such as receptacles with caps or with sliding receptacle covers because receptacle caps may be lost and also may be a choking hazard for some ages. Children can learn to defeat sliding receptacle covers when they watch their parents. TR receptacles provide security against the insertion of objects other than cord plugs into the energized parts.

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How do tamper-resistant receptacles work?

Tamper-resistant receptacles feature built-in shutter systems that prevent foreign objects from touching electrically live components when they’re inserted into the slots. However, the shutters don’t impair normal plug insertion, removal or function.

Automatic Protection

TRRs look just like ordinary outlets, but are designed with spring-loaded receptacle cover plates that close off the receptacle openings, or slots.

When equal pressure is simultaneously applied to both sides, the receptacle cover plates open to allow the standard plug to make contact with the receptacle contact points. Without this simultaneous pressure, the cover plates remain closed, preventing insertion of foreign objects and protecting your children from painful, traumatic electrical injuries.

Are tamper-resistant receptacles 100 percent tamper-proof?

Tamper-resistant receptacles have mechanical shutters that prevent insertion of such single-pronged objects as hairpins, keys, and nails. Data show this to be the most common cause of electrical injuries in young children. The devices don’t protect against two single-pronged items inserted simultaneously—the shutters would interpret that situation as a two-pronged plug, allowing insertion.

Determined adults and adolescents could potentially bypass the mechanism with significant effort. However, UL test standards ensure integrity and performance under normal circumstances.

Although not widely used in homes until recently, TRRs have been required in hospital pediatric care facilities for more than 20 years. In fact, TRRs have proven to be so effective that the National Electrical Code (NEC) now requires them to be installed in all new home construction. Existing homes can be easily retrofitted with TRRs using the same installation guidelines that apply to standard receptacles. TRRs should only be installed by a licensed electrician.

What is the NEC?
The NEC is the National Electrical Code. The NEC’s mission is to provide practical safeguards from the hazards that arise from using electricity. It is the most widely adopted safety code in the world, and it is the benchmark for safe electrical installations. The NEC is an evolving document, developed through an open consensus process. A new edition is issued every three years.

New UL testing

In April 1994, specific UL testing requirements and product markings became a requirement for a tamper-resistant receptacle to receive a UL listing. The UL testing measures the performance, against minimum standards, of the receptacle’s internal mechanism that prevents the insertion of inappropriate objects. Prior to this, there were no specific tests for tamper resistance; all that was available was the UL 498 requirements for a standard receptacle.

The new testing procedure requires a probe test, impact test, mechanical test, and dielectric test, details of which follow.

Probe test. This test tries to defeat the safety mechanism by inserting a single weighted (8 oz.), .031-in. die probe into the blade opening in the face of the receptacle. The probe is then manipulated in an effort to defeat the system and make contact with the receptacle’s contacts.

Impact test. This physical abuse test uses a 1.18 -lb, 2-in. die steel ball, which is swung on a pendulum, to make direct contact with the face of a mounted tamper-resistant device, with an impact force 5 ft-lbs. After this test, the probe test is repeated.

Endurance test. This is a cycle test in which a plug is inserted and removed from the device 5000 times, after which the probe test is again repeated.

Dielectric test. This test is performed after the impact and endurance tests. It tests for internal shorting, with twice the device’s voltage rating plus 1000V applied for 60 sec.

After passing all of the above performance tests, all tamper-resistant receptacles must have either the words “tamper resistant” or the letters “TR” (minimum 3/16 in. high) on the device as a clear indication that this is a tamper-resistant receptacle.

UL (Underwriters Laboratories) is an American worldwide safety consulting and certification company headquartered in Northbrook, Illinois. It maintains offices in 46 countries. UL was established in 1894 and has participated in the safety analysis of many of the last century’s new technologies, most notably the public adoption of electricity and the drafting of safety standards for electrical devices and components.


UL provides safety-related certification, validation, testing, inspection, auditing, advising and training services to a wide range of clients, including manufacturers, retailers, policymakers, regulators, service companies, and consumers.

UL is one of several companies approved to perform safety testing by the US federal agency Occupational Safety and Health Administration (OSHA). OSHA maintains a list of approved testing laboratories, which are known as Nationally Recognized Testing Laboratories.

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