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 before giving any electrical how-to information: Don’t do any of this work if you’re not qualified. You could get electrocuted or start a fire. This is only an overview.
Definition: When I say 'double tap', I'm actually not using the correct terminology; this is just what a lot of home inspectors say when two conductors are connected under one screw or terminal inside a panelboard. There is no official term for this, so double tap works for me. Sometimes this refers to two conductors at one circuit breaker, other times it refers to two conductors connected under one screw at the neutral bar. Today I'll be discussing two conductors connected to a single circuit breaker.
When it's NOT a defect: Double tapped wiring is ok if the circuit breaker is designed for two conductors. If a circuit breaker is designed for two conductors, it will say so right on the circuit breaker, and the terminal of the circuit breaker will be designed to hold two conductors in place. The circuit breaker shown below is an older Square D designed to accept two conductors. I highlighted and enlarged the portion of the label that says two conductors can be attached. This is acceptable. The only manufacturers that make circuit breakers that are designed to hold two conductors are Square D and Cutler Hammer... but not all of their circuit breakers can be double tapped.
Here's a newer type of Square D circuit breaker - instead of putting a bunch of text on the front of the circuit breaker, they now just have a little picture on the front of the breaker.
They now put the text on the side of the breaker.
When it IS a defect: This is a defect when the circuit breaker isn't designed for two conductors; most aren't. It doesn't matter if it's just a simple doorbell transformer wire that's added on to the circuit breaker - the issue isn't about the load imposed on the circuit, it's about the physical connection.
Why it's a problem: If the circuit breaker isn't designed to hold two conductors, the conductors could come loose at some point in the future, even if they feel very tight today. Loose conductors 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 the most common repair, and it's ridiculously simple. The offending conductors simply get disconnected from the circuit breaker, connected to a single conductor with a wire nut, and that single conductor 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 conductors, as long as the panel is designed for it. This would be more involved than the pig tail repair, and I don't know why anyone would want to do this, but it would certainly be acceptable.
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, in part because the bathroom receptacles can't be on a shared circuit (and the bedroom circuit needs AFCI protection - more on that another day). In this case, the conductors 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 conductors split off to the two different circuit breakers.
Install A Tandem Breaker If the panelboard 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. This is basically a way to install two circuit breakers in one space.
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, no tandem 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. This would take some shuffling around, but it wouldn't be a big deal to do.
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.