The majority of the older homes, and a few newer homes I inspect have electrical panels with different brand and type breakers inside them. It seems like I am always writing in my reports this statement, "A breaker in the electrical panel is of a different brand from the panel enclosure. The compatibility of the breaker to the panel needs further evaluation." So what is the big deal about this?
My job as a home inspector is to look at electrical panels in the home and determine if there are any safety concerns with the panel and its components, if there is any damage to the panel and it's components, and if the panel and components have been installed correctly. One of the first things I look at is the panel label. This is my standard to go by to determine if the components are installed correctly. Almost always this panel label tells me what type of breakers should be installed in the panel, and sometimes there is a warning against installing other type of breakers. Below is a photo as example:
The reason why the breakers and panel should match is pointed out in the above photo. As the label above says, each manufacturer have their panels tested with only their breakers. Manufacturers don't test other brand breakers in their panels. Breakers must be UL listed and certified for each panel to ensure proper operation. A UL listed and certified breaker is a manufacturers breaker tested with the manufacturers equipment that has met the Underwriters Laboratory safety standards. These are the breakers most manufacturers want electricians to use in their panels.
A UL classified breaker is another manufacturers breaker tested with with another manufacturers equipment that has met the UL standards. Like UL listed breakers, UL Classified breakers have been tested only in the panels for which they are approved, so it does not mean they are interchangeable with all other panels. These UL certified breakers are also called "interchangeable" breakers. Some manufacturer’s accept "interchangeable" breakers, but others give warnings of voiding their warranty if these breakers ared used.
Determining whether UL classified breakers are compatible with a panel is beyond the scope of my inspection and expertise. This is why I always send a panel with different breakers to a licensed electrician. When in doubt, always install breakers that are specified for your panel.
When you really want to know about your electrical panel, hire Adam Duncan of Duncan Home Inspection Services. It would be my pleasure to help.