Double tapped circuit breakers are one of the most common electrical defects that I find while doing home inspections in Minneapolis and Saint Paul, and they're usually one of the easiest defects to correct. Today I'll explain what double tapping is, when it is and isn't a problem, why it's a problem, and how to correct this condition.
I didn't consult with an attorney before writing this article, so I feel like I should add a disclaimer: This blog is only an overview of what an electrician might do. Don't try to do any electrical work if you're not qualified.
Definition: I don't know of any official definition of a 'double tap'. This is just what us home inspectors say when two wires are connected under one screw or terminal inside an electric panel. Sometimes this refers to two wires at one circuit breaker, other times it refers to two wires connected under one screw at the neutral bar. Today I'll be focusing on improperly double tapped circuit breakers.
When it's NOT problem: Double tapped wiring is ok if the circuit breaker is designed for two wires. If a circuit breaker is designed for two wires, it will say so right on the circuit breaker, and the terminal of the circuit breaker will be designed to hold two wires in place. The circuit breaker shown below is designed to accept two wires, and I highlighted and blew up the portion of the label that tells me that two wires can be attached. This is acceptable. To my knowledge, the only manufacturers that make circuit breakers that can be double tapped are Square D and Cutler Hammer... but not all of their circuit breakers can be double tapped.
When it IS a problem: This is a problem when the circuit breaker isn't designed for two wires. The label on the circuit breaker will clearly state this.
Why it's a problem: If the circuit breaker isn't designed to hold two wires, the wires could come loose at some point in the future, even if they feel very tight today. Loose wires can lead to overheating, arcing, and possibly a fire.
How to fix: The fixes I'm going to list below are a few common ways of dealing with double tapped circuit breakers.
Pig Tail This is usually the easiest and best repair. The offending wires simply get disconnected from the circuit breaker, connected to a single wire with a wire nut, and that single wire gets connected to the circuit breaker. Now, I know what you're thinking: "What's so tough about that?" The answer is nothing. This is a quick and easy fix.
Different Circuit Breaker Another simple repair would be to replace the circuit breaker with a type that is designed for two wires, as long as the panel is designed for it.
If there are more problems going on besides just a double tap, the repair might get more involved. For instance, if a homeowner finished off a basement and added a circuit for the basement bedroom on to the circuit breaker for the bathroom receptacles, simply adding a pig tail for the wires wouldn't be a proper repair, because the bathroom receptacles can't be on a shared circuit. In this case, the wires would need to be split off on to two separate circuit breakers. There are a few ways to do this.
Add A Circuit Breaker If there is room in the panel, another circuit breaker can be added, and the wires split off to the two different circuit breakers.
Install A Tandem Breaker If the electric panel is designed to use tandem breakers, and a tandem breaker can be properly used in lieu of the offending circuit breaker, this is another acceptable fix. Some people refer to tandem breakers as half-height or half-size breakers. This is basically a way to install two circuit breakers in one slot.
If a panel will accept tandem breakers, it will say so inside the panel, and the specific locations where tandem breakers can be used will be identified. A panel may allow all tandem breakers, notandem breakers, or some tandem breakers. The photo below shows a panel that allows some. As you can see, eight more circuits could be added to this panel, as there are currently no tandem breakers being used.
When none of the above solutions are possible, the repair might involve replacement of the panel with a larger one, or the addition of a subpanel. This would obviously get much more expensive.
Reuben Saltzman, Structure Tech Home Inspections