Why Do Outlets Have Different Types of Holes?

As electricians, we are called upon to install (among other things) many different types of receptacles to give our clients something to plug their equipment into. But why do the receptacles look so different from one another. In the latest episode of Electrician U, Dustin dives into this topic to give our followers answers to their questions.

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Let’s start with the standard 120v receptacle. A standard 15a receptacle has 2 vertical slots (one each for the hot and neutral) and a dome-shaped for the ground, while the 20a receptacle looks almost identical but the neutral slot also has a horizontal opening. The reasoning is rather simple. If you had a piece of equipment that draws 15 amps, you can plug it into either a 15a or a 20a receptacle, as the receptacle is rated for it. If you had a piece of equipment that draws 20a, you can only plug it into a device rated for 20a otherwise it could potentially melt, as it draws a higher amperage than the device is good, for and start a fire. Something to consider, especially in the fall/winter months, is to be mindful of plugging in smaller temporary space heaters and overloading your circuitry. If you have a string of 15a devices wired to 20a breakers, its very easy to exceed the receptacles ratings and run the risk of a fire.
Another question is why are some of the slots on a receptacle larger than the others? If you are looking at the face of a standard 15a receptacle, you will immediately see that the left (neutral) slot is a bit larger than the right (hot). This is done so that you only plug the cord in, as intended, and provide whatever you are plugging in the proper polarity to each pole. In other words, it is meant for you to plug your equipment neutral into the neutral slot and the hot into the hot slot. By the neutral slot being bigger, it simply will not fit into the smaller hot slot. If the equipment is not affected by polarity or has a ground prong (so it can only be plugged in one way) the blades will be the same.
A single (or simplex receptacle) has only 1 spot to plug something into it. This would be for something that draws close to the circuit’s ampacity (like a chest freezer for example) or maybe something that you don’t want to share circuitry with (like sensitive electronics). A duplex receptacle, however, is the standard receptacle we see and use for most applications. This device has 2 places to plug into on the same yoke. If you were to place 2 duplex receptacles in the same box, you would consider that a quad, and would have 4 places to plug something into.
Device shape is also something to consider when installing receptacles. Standard or Decora? Standard receptacles are the normal ones we are used to seeing where the face of the receptacle takes on a rounder appearance with each place to plug into looking individual, while the Decora type receptacles are a single looking device with a pronounced square shape. Decora type devices not only look a bit nicer, but they also carry the added benefit of having the same type of plate for ALL the Decora switches, receptacles, GFCI’s, Etc.
The last part for Dustin to dive into is the 250v type receptacles. These would be the larger receptacles you would find in your home for the dryer or range (among others, but those being most common). They look considerably larger as they are rated to carry more amperage and voltage than our standard receptacles, but they are constructed similar, in that they have different slots that do not allow you to plug something into a device that it isn’t rated for.

#electrician #electrical #electricity

0:51 - Examples of Receptacle's
2:28 - Chord examples - Polarity
3:43 - Receptacle types
4:40 - 250 V Receptacles
6:30 NEMA Plug Diagram