Tech In Plain Sight: Field Guide To Power Plugs

It is the bane of worldwide travel: there isn't just one way to get AC power from the wall. The exact connector — and what you can expect when you plug in — differs from country to country. Even if you stay home, you must account for this if your designs go places and expect to plug into the wall. If you’ve ever looked at a universal adapter, it is full of prongs and pins like a metallic porcupine. Where do all those pins go?

Of course, there are some easy ways to sidestep the whole issue if you don't need AC power. Much low-power gear now just provides a USB or barrel connector. Then you can use an area-appropriate adapter or charger to power your device. Batteries work, too. But if you need to plug in, you will run into other kinds of plugs.

Switching power supplies have helped. In the old days, many things expected either 125V or 250V and didn't work with the opposite voltage. Switching power supplies often allow a wide input range or have a switch to select one range or the other. These two voltages will cover almost any situation. If you have something that must have one voltage or the other, you’ll need a transformer — also called a converter — to step the voltage up or down. But most often, these days, you just need an adapter. There are slight variations. For example, some countries supply 100V or 110V, but that usually doesn't make much difference. You also need to understand if your equipment cares if the AC is 50 Hz or 60 Hz.

Most of the power sockets you’ll find around the world will fall into one of several categories. The categories range from A to N. Even among these, however, there are variations.

For example, the common type A plug and socket are what Americans call "two prong." If you live in the US, you’ve probably noticed that the plug is polarized. That is, one pin is slightly wider than the other so the plug can only go in one way. The wide pin is connected to the circuit neutral. The maximum load for this connector is 15A. It is difficult to find type A sockets anymore, other than on cheap extension cords or things like lamps that pass through their electrical connections to a second socket. Type B is far more common and type A plug will fit in a type B socket.

In Japan they also use type A. However, Japanese type A plugs have two blades of equal size. They’ll fit into a US socket, but not the other way around. Type A is also found in most of Central America and the Caribbean. The two pins, of course, are the AC hot and neutral wires. This is also called a NEMA 1-15 connector, although you may have never heard of that. The Japanese version is technically a JIS C 8303 class II. Typical voltage is 125V for the US variant and 100V in Japan, both at 15A. In China, type A sockets carry 220V.

These days it is more common to see type B sockets or what Americans would call a "three prong." These are used in most of the same countries that use type B and the Japanese plug is slightly different, again. The type B plug has the same two wires as a type A plus a ground lug at the bottom. Because of the orientation, it can only go in one way. In addition, the ground pin is slightly longer, so it will make contact before the other pins and stay in contact longer when removing the plug. It is possible to plug an A plug into a B socket, but there will be no grounding, of course. Also called a NEMA 5-15, this plug is also rated at 15A and like type A, typically carries 110V. The Japanese variant, JIS C 8303 class I carries 100V at 15A.

If you’ve been in Europe, you’ve seen type C plugs (CEE 7/16 or CEE 7/17) but the corresponding sockets are not used anymore. Sometimes called a Europlug, they are used in most of Europe with a few notable exceptions (Great Britain, Ireland, Cyprus, and Malta). You can also find them in China and Russia. They are rated to 2.5A (CEE 7/16) or 16A (CEE 7/17) and fit in E, F, J, K, or N sockets. Often, the pins are tapered and flexible to help them fit in various socket configurations. They also fit into some L sockets, but since the high-current L socket has a different spacing, they won't accept a type C plug. If you had a type C socket, it would fit there, too, but without grounding, these have mostly been replaced. You usually find 250V on these plugs. There are minor variations between countries, and while a British BS 4573 is a type C socket, it won't accept a Europlug because of different pin sizes. The BS 4573 is an "electric razor" plug meant for plugging into isolation transformers near sinks.

New type H sockets have holes within the slots that allow you to fit a type C plug into the socket. The type O, found in Thailand, can accept a type C, also, but a difference in pin size often causes a loose fit.

Notice that the pins are insulated towards the plug body. This prevents exposed energized conductors while plugging into a compatible socket. The metal parts are only hot when they are covered by the socket. However, the CEE 7/17 plug lacks this insulation and uses fatter pins to increase current for things like hair dryers or vacuum cleaners. Because of the plug body's shape, these will not fit into a type N socket.

The type E, F, J, K, L, and N are all similar to a type C, but the socket has some arrangement for ground. This is similar to how the type B socket has a provision for a ground but can still accept a type A plug. A C plug will mostly fit in any of these sockets, although there are some limitations, especially with the type L socket, which is really two incompatible sockets.

The type E has a male pin that serves as a ground installed at the top as opposed to type K, which has the male ground pin on the plug. Type E are common in parts of France, Belgium, Denmark, and Poland, along with a few other countries. The type K outlets are found in Greenland, Denmark, and some other countries.

The type F found in countries like Algeria, Bosnia, and Iceland, among others has grounding pins on the side. These are sometimes known by a shortened version of their German name, the Schuko plug.

Type J appears in Switzerland and a few other countries. It is often called a "Swiss 3 pin." The SEV 1011 is rated for 10A and there is a variant that can handle up to 16A. There is also a two-pin plug that can be made to fit in a type J or type C socket. Most often, you’ll find 220V on these connectors. Type K is found in Denmark alongside C or E sockets.

Thailand is the home of type O, a 16A 250V connector with ground. a C , E, or F plug will fit in an O socket loosely.

The type L, used in Italy and North Africa, is the odd connector out of the ones that can take a type C plug. These distinctive plugs have a single row of three pins. The 10A version will accept a C plug. However, the 16A version is spaced wrong because, historically, there was a 127V circuit for lights and a 220V circuit for everything else and they used different plugs. In modern times, the sockets often have a figure 8 pattern on the outer holes so they can accept either version of the plug and these will take a type C plug.

The built-in fuse allows homes to utilize "ring circuits." That is, instead of a small number of outlets being fed from a branch leaving a central point like a load panel, all outlets can connect to each other in a ring. This means that the central distribution is simplified, but has a much larger circuit protection device than in a radial system. Therefore, each thing that plugs into the ring needs its own, presumably smaller, fuse.

You might think this is everything, but it isn't. There are also plugs made for electric shavers and endless variations for high-currents or special functions. Then there are connectors for, say, 220V three-phase in the US. Truly a case of the old adage, "The nice thing about standards is that there are so many of them."

Many of the plug and socket pairs cover a lot of countries. The handy map below shows what regions use what (although Thailand's type O seems to be absent; you’ll find A, B, C, F, and O there). Might come in handy if you need to quickly figure out what kind of plug you are dealing with.

We didn't use any images from the site, but if you want to see real pictures of pretty much everything, there is the Digital Museum of Plugs and Sockets, proving that you can, indeed, find almost anything on the Internet. For a more technical and interactive experience, there's always the IEC which helpfully tells you the voltage and frequency to expect, too. How did we arrive at all these plugs? There is some history about that. If you want to get up close and personal with a BS1363 (type G) we can help with that, too.