When You Can’t Go Wireless Go NEMA

The 20th century brought in the establishment of the International Electrotechnical Commission (IEC) for setting standards and requirements of electrical components. This led to the formation of the National Electrical Manufacturers Association to standardize electrical equipment and oversee safety standards for consumers in North America. This is the industry authority in the US and is composed of 350  companies and has over 700 standards and technical publications.

Unlike the IEC, NEMA products are designed for:

  • Ease of selection
  • Have a broader application
  • Are sold fully assembled
  • Require safety covers
  • device is larger
  • withstands short circuits better
  • For North American markets

NEMA connectors

NEMA quality standards are followed by manufacturing electrical plugs and receptacles in the USA. The two most popular connectors are:

  • NEMA 1-15P
  • NEMA 5-15P

They have bodies of rubber and steel or brass prongs.  Other connectors have increased voltage and differently placed prongs. The first number represents the plug type, for most outlets in America, it will be NEMA1 or NEMA5. The second number shows the total amps passing through the connection, followed by the R or P meaning receptacle or plug.

Connectors are divided into two categories


These connectors have curved prongs that can be locked into place by twisting them. Locking connectors are to prevent accidental disconnection or dislodgement. Being designed for commercial and industrial use the key is safety. 

Where the larger types of locking connectors do not fit there are miniature connectors. These midget connectors are identified with an “ML” and “L” placed before the series to differentiate locking connectors from the others.

  • ML-1, two-pole, no ground,125V
  • ML-2, two-pole, grounded, 125V
  • ML-3, three-pole, no ground (hot-neutral-hot), 125V

The design of locking connectors allows different voltages and current ratings to be intermated.   This includes connectors for boats, 400Hz circuits for aircraft and then there are direct current applications.

The disadvantage of lock connectors is that when a cable is pulled too hard, exposed connectors may be exposed. This can cause shock and dangerous shorts.  The result is that in most cases     connectors have a strain relief.

Non locking

These connectors have straight blades instead of prongs and are used for everyday applications like computers, appliances, etc.   their disadvantage is that they can easily be pulled out of receptacles. The most common connectors in this group are the NEAMA 1 which is slowly being phased out and the NEMA5 that comes with two blades without the ground or grounded option. 

  • NEMA 1 – has two flat blades and is non-grounded with two poles wired rated 125V. Unfortunately, this popular configuration is being phased out. Since 1962 builders have been required to install NEMA 5 ground plugs instead of NEMA 1 but they remain in older buildings and are still available for repair. 
  • Since 1974 New power outlets are required by law to be grounded and the use of NEMA5-15 and  NEMA5 -20 are typically used. The popular Nema 1 plugs are still used by some small appliance manufacturers because they are cheaper.
  • NEMA 5 –  Has two blades one wider than the other, with a grounding pin, three wires, and two poles.  There are the NEMA 5-15 – and -30 variety that plugs into the NEMA 5 receptacles
  • The Electrical Safety Commission has warned not to remove the ground pin.  In addition to line/neutral polarity being lost, there is an obvious danger in removing the pin.
  • Rest assured if you have a NEMA 5-15 as this is the standard connector for the US and you will be able to plug in anything you want.

Safety features

Test and reset buttons

To address specific shock hazards, electrical codes in America began to require added safety features in NEMA5-15R and -20R. These receptacles are residual current devices.  Protection is required in potential wet locations like bathrooms, outside, etc. Test and reset buttons are required and in some cases indicator lights.

Tamper-resistant receptacles

To address shock hazards with children the National Electrical Code requires a tamper-resistant receptacle since 2008.  These TR receptacles prevent electricity from energizing objects stuck into the receptacles and are effective against electrical shock. The spring-loaded shutters close off contact opening. Only when both shutters are pressed will they open.

Power connectors and receptacles are available in numerous configurations. Therefore it is important to work with qualified engineers when choosing an electrical installation.