If you’ve ever peeked inside an electrical panel, you may have seen multiple wires crammed under a single screw. This practice is often called double tapping or double lugging. It might look harmless, but it’s actually a wiring mistake that can lead to overheating, loose connections, and even fire hazards.
The General Rule
The golden rule is simple: one wire per terminal — unless the terminal is specifically designed to accept more. Every circuit breaker, neutral bar, ground bar, and main lug has its own manufacturer’s instructions, and those instructions matter.
Most circuit breakers you will find in homes today only allow a single wire under the screw terminal. A few breakers may accept two wires, but only if they are specifically labeled for it; otherwise, it’s illegal.
Some Square D breakers, for example, are designed to accept two wires, one on each side of a special clamp. But three? Never. If a breaker or bar isn’t clearly labeled for multiple wires, then only a single wire belongs there.
Neutral Wires (the “return path”)
Neutrals are especially important. Each neutral wire must be connected to its own individual screw. Sharing screws can cause arcing, loose connections, and headaches when troubleshooting later.
- No doubling up neutrals. One screw, one wire.
- No mixing neutrals and grounds. Even though they meet at the main panel, they still require separate terminals.
Ground Wires (the “safety net”)
Grounding wires (EGCs) are a little more flexible than neutrals. Some panel manufacturers allow two or even three ground wires under a single screw, but only if the panel instructions specifically say so. And in subpanels, grounds and neutrals must always be kept on separate bars.
The Exception for Ground Wires
There is an exception to the “two identical wire per screw” rule. In certain panels, the manufacturer allows three ground wire under the same screw.
Here’s what that looks like:
- Main service panels only: In the main panel (the one with the first disconnect), unused neutral holes can sometimes be used for ground wires.
- How many wires: Depending on the panel, one larger ground (#14–4) or up to three smaller ones (#14–10) may be permitted.
- Wires must match: If more than one wire shares a hole, they must all be the same size and material (all copper or all aluminum). Mixing sizes or types leads to loose, unsafe connections.
- Read the fine print: This is only allowed if the panel’s labeling and instructions clearly permit it.
Most panels you’ll find in homes today do not allow this. If you see multiple wires squeezed under one screw without that specific approval, treat it as a defect.
Breaker Terminals and Main Lugs
For breakers and main lugs, the rule is clear: one wire per terminal, unless it’s labeled otherwise. Ignoring this creates unsafe conditions, and it can also void the manufacturer’s warranty on the equipment.
Why It Matters
To the untrained eye, double tapping might look like a shortcut. But to a trained inspector, it’s a red flag that says: someone cut corners here. That’s why understanding details like these is such an important part of the home inspection profession.
Thinking About a Career in Home Inspection?
Catching issues like double tapping is just one example of the skills you’ll learn as a professional home inspector. If you’re curious about the field, our next Fundamentals of Home Inspection course starts October 6th. We’d love to teach you how to turn details like this into a rewarding career.
