NEMA and IEC Connectors

Imagine this - it is the graveyard shift and you have comfortably settled into your air-conditioned cubicle overlooking the data center, plugged in your laptop next to the UPS station and are now ready to go and check the electric kettle you left on the hot plate for brewing the coffee that would go with the sandwich you intend to heat in the microwave in the break room. Ever imagined, in this set-up, how many different kinds of electrical connectors are involved to let us do our daily chores, the little things that we hardly notice and take for granted? Believe it or not, in this little scenario alone there would be 3-4 different types of connectors in play, all perfectly playing their own specific role in the jigsaw puzzle of modern day life!

Curious? Read on!

In the US, there are standardized templates for almost 50 (yes, read it right!) different connector configurations, based on two primary standards, the IEC and NEMA. Let us take a quick look on both, including the different types, recommended voltages and currents, common uses, focusing on the most common ones. Time to say, “Beam me up, Scotty!”

First the IEC connectors.

To give a perspective, the IEC set of standards is followed according to the established guidelines of the International Electro-Technical Commission (IEC) in order to standardize connectors across manufacturers and geographies. As a general rule, IEC standards deal with a rated voltage (AC) not exceeding 250 V @ 50 Hz - 60 Hz, with a rated current limited to 16 A. The pin temperatures (not to be confused with the ambient temperature; rather this is the temperature measured where the pin emerges from the engagement surface) are 70 °C, 120 °C, and 155 °C depending on the IEC connector type.

IEC appliance couplers are designated by identifiers starting with "C" with a trailing number such that the appliance inlet identifier number is 1 more than the corresponding cable connector (e.g. C15-C16 constitute a connector-receptacle set).

While we generally come across only four to five major types of connectors, there are in fact 24 of them specified in the standard sheet, 2 of them being obsolete and no longer used. Out of the most oft used IEC connectors are the following:

C13-C14: The most common type per se. These can be seen in most of your everyday objects like computers, desktop monitors, printers, UPS devices etc.

C15-C16: Similar to the above, but are earmarked for hot appliances like electric kettles, coffee makers, PoE switchers, network closets etc.

C17-C18: Well, these too are similar to the good old C13-C14 but without the grounding pin. You can find it in your XBOX 360 power block.

C19-C20: Favorite for server room and data center PDU engineers, feeding on higher currents. Used in various medical and test equipments as well. Would appear to what some refer to as the ‘squared version’ of the C13-C14.

Apart from these, C5-C6 and C7-C8 connectors are also widely seen on grounded and non-grounded laptop power supplies respectively. Although rare, C6 & C8 power bricks with ratings up to 300 W also exist.

Tip: As a thumb rule, C13 & C15 are cold and hot connectors with pin temperatures at 70 °C and 120 °C respectively. Interestingly, there are two other sets used for ‘very hot’ configurations with pin temperature rated at 155 °C : C15A-C16A and C21-C22.

Whether you are just curious or would love to have a ready-reckoner around, the following table might immensely help and act a quick go-to reference for typical IEC connectors:

On the other hand, the NEMA set of standards is followed according to the established guidelines of the US based National Electric Manufacturers Association (NEMA) in order to standardize connectors across North America and few other countries. As a general rule, NEMA standards deal with a rated voltage (AC) between 125-600V, with a rated current from 15-60A. NEMA 5 series most common in the US , rated to a maximum of 125V(usually carries around 110V though!). NEMA 6 series connectors are to power heavy duty devices, typically on 208- 240V circuits.

The naming convention of NEMA connectors constitute a number followed by a hyphen, which in turn, is followed by another number. The number preceding the hyphen indicates the particular configuration, voltage to be used and power-phase. The trailing number indicates the current rating. A letter at the beginning indicates whether it is a locking type (prefixed ‘L’) and another letter at the end specifies if it is the male connector (‘P’) or the female receptacle (‘R’). The locking type connectors are curved blade types, as opposed to the other straight-blade NEMA connectors and are typically used for heavy commercial and industrial equipment to guard against accidental disconnection.

Confused? Well, perhaps an example could help.

Consider L5-30R; it would be a Locking 2-pole 3 wire (2+3=5, you see!), rated for 30A Receptacle. Simple, you see!

TIP: NEMA connectors not following this nomenclature: the small sized ML series ("Midget Locking" connectors), TT (Travel Trailers or RV connector), SS series ("ship-to-shore" connecting boats to shore power) and the FSL series (military & aircraft).

While we generally come across only four to five major types of connectors, there are in fact around 25 of them specified in the standard sheet, few of them being obsolete and a few reserved for future configurations ( interesting, you see!). Out of the most common NEMA connectors are the following:

NEMA 1-15P (2 pole, no ground) and NEMA 5-15P (2 pole + ground pin) connectors are most commonly used in everyday domestic equipments. Fit into standard 110 V wall outlets

NEMA 1: Standard for 2-wire non-grounded devices like basic electric lamp or non-grounder power cord of a laptop etc. NEMA 1-15R receptacles now prohibited in new constructions but available for repair use. Still popular with small appliances and electronic devices manufacturers due to low cost and compact size (permitted on double-insulated devices and appliances not needing grounding). Upward compatible with grounded NEMA 5 receptacles.

NEMA 5: Basically the most common type. Found on most 3-wire grounded electronic devices like surge protectors, computers, standard extension cords etc.

NEMA 14: 4-wire grounding devices. 14-30 is common in clothes dryers and 14-50 in stoves and RV parks respectively. The 14-30 has the top blade shaped like an "L", while the 14-50 got a straight center blade guarding against accidental use of a 14-30 on a 14-50 receptacle.

NEMA TT-30: Favorite for RV parks. Rated for 125 volts, used by most RV's. Guess what, the TT in the name stands for Traveler Trailer.

And yes, Tesla recommends NEMA 14-50 as the connector for home charging of electrical vehicles.

TIP: For NEMA 5-20R and 6-20R straight blade connectors, the receptacle can accept either the 20 or 15A plug by using a special "T" shaped slot.

TIP: Some NEMA plugs have a small hole near the end of the non-ground blades, allowing physical lockout of hazardous equipment by using small specialized padlocks.

TIP: Though NEMA wall receptacles can be installed in any orientation National Electrical Installation Standards (NECA 130-2010) specify that the preferred location of the ground is on top.

TIP: NEMA 1-20R and 1-30R do not exist, as 1-20P & 1-30P mates with corresponding NEMA 5 R.

As before, the following table might act as a ready reckoner:

Tip: New residential constructions now require tamper resistant receptacles for ensuring child safety and disallow items like keys or paper clips inserted into the socket. An interlocking mechanism is now mandatory and requires hot and neutral blades to go in simultaneously to open the doors guarding the slots.

Tip: According to the Electrical Safety Foundation International: "Never remove the ground pin (the third prong) to make a three-prong plug fit a two-prong outlet." May be a no-brainer, but be sure to remember this when you are in a hurry to test that wow appliance you bought on your foreign trip and cannot wait to test it NOW!