As a home inspector, I come across a variety of issues regarding electrical wiring. One of the most common safety defects I see is double Lugged breakers. I thought I'd just take a minute to explain what this issue is, and why a home inspector will call it out as a safety concern.
The 3 breakers on the upper right side all have 2 black wires entering in the back and held by a single flat screw. This is wrong for a couple reasons. First, it's against the NEC (electrical code). "NEC 110.14(A) Terminals: .... Terminals for more than one conductor and terminals used to connect aluminum shall be so identified." In other words, if the breaker is not approved and labeled for 2 conductors (black wires), it is not allowed.
I am aware of only one panel brand (Square D) that makes some breakers that allow 2 conductors. It's designed for that application as it has a special washer that accomodates these 2 wires. See below.
So, why is it a safety concern if not approved? Mainly, the issue is that the screw holds the wire securely to a conductor connected to the bus bar. If there are more than one wire being held by a flat screw, one could more easily become loose and start arcing. This is especially true when 2 different size wires are present such as 14 gauge and 12 gauge.
I most often see this issue when the panel is full and there are no more places to add breakers. The solution often is to pigtail these breakers or in some cases add a sub panel. In other cases, it makes sense to upgrade to a larger panel depending on what else might be going on inside the home.
Home this helps.