What is a Double Tapped Neutral
Double Tapped is a slang term used to describe when 1 of the screws on the neutral bus bar in the panel board has more than 1 neutral wire feeding to it.
Reasons Why This Is an Issue
Isolation and Repairs
When two neutrals are wired together on a single terminal within the panel box so that the circuit can be isolated if it needs to be worked on. For one neutral to be disconnected, other neutrals from energized circuits sharing the same lug will be loosened. Power surges may result on the energized circuits.
Lose connections can lead to fire
When more than one neutral wire is connected under a single lug, the additional thickness can cause loose connections or connections that will loosen over time. These improper connections can cause arching. Arching is when two electrodes produce a plasma discharge. This arching in the circuit could start a fire.
Overheater Connection at a Double-Tapped Neutral Lug
The image to the right illustrates the heat build up from the double-tapped lugs in the panel box. Image taken with a thermographic, infrared camera
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Why would this affect me?
Having double-tapped neutrals in your panel box is more common than you might think. The code was not clearly spelled out in the National Electric Code until 2002. The recommendations by panel box manufacturers can also be unclear. A licensed electrician can determine if you have double neutrals and recommend options to rewire your panel box safely and correctly.
The Science of it
Current
An electric current is the rate of flow of electric charge past a point or region. An electric current is said to exist when there is a net flow of electric charge through a region.
Neutral
The purpose of the neutral wire is to complete the 120volt AC circuit by providing the path back to the electrical panel where the neutral wire is connected and bonded to the earth ground.