A “double tap” is when two wires are under the same lug (screw) in an electrical panel. As an inspector, I see double taps all the time, and I’d like to address the issue to provide some clarification for anyone who has seen this issue come up in their home inspection report.
In my neck of the woods, double taps are very common. In fact, very few panels that I inspect are free of double taps. Often times, they exist because the electrician simply ran out of room in the panel, but other times there’s plenty of space and the double taps are an indication of sheer laziness on the part of the electrician. Double taps can exist at breakers with hot (black) wires or at bus bars with neutral wires. Double tapping is permitted with two grounding wires but not with hot or neutral wires. Neutral wires are frequently double tapped with grounding wires, and this is also prohibited. This is because hot and neutral wires are energized (have continual electrical current) and need a secure connection for the electrons to move along their intended path. The metal screws provide this secure connection, and placing two or more wires under the same lug makes it less likely that a completely secure connection can exist.
Without a secure connection of energized lines, arcing and other shock or fire hazards are more likely to occur. If a panel has run out of room and another circuit is desired, it’s relatively easy and inexpensive for an electrician to simply add another hot wire to a breaker. Likewise, if a bar is full with neutral and ground wires, the most simple and cost effective way to solve the problem is to just double up the wires. Unfortunately, these options, while simple, are prohibited for safety reasons.
If there is not enough space in the panel to avoid double tapping, the best options (which comply with modern safety standards) are to either add a sub panel that feeds off the main panel or to upgrade the existing panel to a greater service amperage. Either option will solve the problem of double tapping and prevent shock and/or fire hazards if done correctly.
Now, I will tell you that most of my electrician friends don’t see much harm in double tapping neutral wires with other neutral or ground wires. You should be aware, though, that these types of double taps are prohibited by the NEC (National Electrical Code), and if there’s one thing I’ve learned as an inspector it’s that codes exist for good reasons. They make sense, ensure safety, and despite popular opinion, are not usually burdensome or unreasonable.
If your panel contains double taps of black hot wires or white neutral wires, you should consider having a qualified electrician make necessary repairs to ensure safety. Yes, it’s possible that you may never have a problem, but it’s always better to be safe than sorry.
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