When it comes to circuit breakers installed in switchboards panelboards and load centers, there are two main types: bolt-on and plug-on (sometimes also referred to as snap-in or plug-in). The main difference between these two types of breakers is how they connect to the bus in the panelboard. There are also differences in their costs, kAIC Interrupting Current ratings, and installation time which we will discuss in this article.
Bolt On Breakers
As the name implies bolt-on breakers are bolted to the panel’s bus (with a screw). Bolt-on breakers are normally used in industrial applications, where larger loads exists and thus the possibility for larger fault currents. A solid connection to the bus via the bolt allows the breaker to be rated for a higher interrupting current (kAIC). The bolt or screw usually fastens onto a smaller bus finger which connects the panel mains bus.
The connection details of a bolt-on type branch breaker in a 3 phase panelboard is shown below:
Plug-on breakers on the other hand use clips to “plug” or “snap” onto a mounting rail (plated conductor) that is equipped only on panelboards that are capable of accepting plug-on type breakers. Plug-on style breakers are normally used in residential and some light duty commercial applications. The ease of snapping out a breaker and snapping in a new breaker without the use of any tools, along with a cheaper price point compared to a bolt-on breaker, makes it an appealing option to homeowners. This however does come with disadvantages. Overtime, the breakers may come lose and even fall off the mounting rail during heavy vibrations, such as an earthquake. As such, plug-on breakers are seldom used in industrial applications, where the sturdier bolt-on breakers are preferred.
The connection detail of a plug-on branch breaker to a residential load center panel is shown below: