How To Properly Use Twist-On Wire Connectors When Performing Home Electrical Work

Twist-on wire connectors, often called wire nuts, were invented in the 1920s by a Canadian electrician named William Marr. Since that time, twist-on wire connectors have become the most-commonly used connector for residential and commercial electrical work. They are popular with professional electricians and home do-it-yourselfers, alike, due to their ease of installation and the creation of reliable, safe connections.

However, the underlying simplicity behind twist-on wire connectors can mislead do-it-yourselfers if they fail to pay attention to their work. There are several problems that can be caused by improperly using a twist-on connector. Below are some of these mistakes as well as information on how to properly use twist-on connectors:

Use the appropriate connector

Even though twist-on wire connectors may look alike, there are a number of widely-varying connectors available in the retail market. Connectors are rated for wire gauge, which is the diameter of the wire, voltage levels, and usage environment. The wire connector industry has adopted a color standard that can help identify which wire gauges are appropriate for use in a given application:

Gray – wire gauges 16, 18, 20 and 22

Blue – wire gauges 14, 16, 18, 20 and 22

Orange – wire gauges 14, 16, and 18

Yellow – wire gauges 10, 12, 14, 16 and 18

Red – wire gauges 10, 12, 14, 16, 18, 20 and 22

In addition, you need to know what connectors are appropriate for use in a given application from a voltage perspective. For example, if you are installing low-voltage landscape lighting that operates at 12 volts DC, then a low-voltage rated connector should be chosen. Conversely, if you are connecting wiring that carries 240 volts AC, then be certain the wire connector is able to sustain the current.

Finally, be sure that your wire connectors are appropriate for the environment in which they will be used. Ordinary connectors are fine for use inside of drywall where there is no expectation of moisture; however, if you are joining wires in an outdoor location where rain, snow and other moisture is likely to intrude, you should choose special filled connectors that create a moisture barrier.

Ensure your connectors are properly tightened

Twist-on connectors are simple to tighten, but that doesn't mean they can't be over or under-tightened. Under-tightening can lead to serious consequences such as loose connections that result in electrical arcing and possible fires. Over-tightening can break wires inside a connector, and that may also lead to a failed connection that can pose dangers for home occupants.

A properly-tightened wire connector should possess the following attributes:

  • Insulated wires leading from the connector have begun to twist around each other
  • Definite resistance is felt when attempting to twist the connector further
  • The twisted wires cannot be readily pulled from the connector, even with moderate effort
  • The wire connector isn't bulging or distorted

If you are in doubt about your connection, the best choice is to untwist it and begin again. If the wire appears to be damaged from the initial attempt, be sure to strip the insulation further to expose clean, bare wire before proceeding.

Don't use with aluminum wires

Aluminum wiring was commonly used in the United States during the 1960s and 1970s, but multiple house fires attributed to aluminum wiring led to the end of that practice. Several existing older homes still have aluminum wiring; if you encounter aluminum wires in your home, be sure that you do not use twist-on wire connectors. Their use with aluminum wires is discouraged for these reasons:

  • Aluminum tends to expand and contract more than copper, and the strands could pull apart inside the connector.
  • Joining aluminum wires with dissimilar metals, such as copper, could cause galvanic corrosion and lead to connection failure.

Instead of using twist-on connectors, choose an approved wiring connection method, such as crimping, for aluminum wiring. Consult with an electrician for assistance or check out sites like to learn more about appropriate methods for working with aluminum wiring.