Split Bus Electrical Panels

“Doesn’t the electrical service panel have to have a main disconnect breaker?” This is a question I get asked over and over. Having a single main breaker is expected, but that has not always been the case. The simple answer to the question, however, is, “No. Probably not.”
Because most electrical service panels are not installed by homeowners or “Uncle Harry,” it is rare to find service equipment without a means of disconnect. There are a couple of ways where it might appear to be missing, but is in fact there after all. I want to keep this post simple enough that most readers can understand what I am talking about.
Real estate agents and homeowners should understand the basic principles so that when the inspector calls for replacement of what appears to be a perfectly good panel, they can understand why.
The first point I will make is that all electrical services to the home must have means of shutting off all the power.
Being able to shut off the power is usually achieved by a main disconnect breaker in the electrical service panel—and should be labeled as such. (I am not going to talk about fuses in this post.) Where it gets a little confusing is when that main disconnect breaker is in a different location from the panel in the home—like outside the home at the electric meter, as in townhouses, condos, and other instances. In these instances, the panel in the home is not the electrical service equipment but is instead called a sub-panel, or remote distribution equipment. This type of panel doesn’t require a main breaker unless it is in a detached structure. Of course, it does no harm to have one, and one is often installed for convenience.
The below picture is of a close to correctly wired sub-panel. This type of panel will not usually have a single means of disconnect; it will be located at the electrical service equipment—typically where the meters are located.

There is another type of panel that looks, at first glance, like it might be missing a main breaker. This type of panel is configured such that it takes a maximum of six disconnects to shut all the power off.

The below picture is of a typical split bus panel with its dead-front cover in place. Notice it says “Service Disconnects” in the center between the upper breakers?

This means that when all those top breakers are turned off, all power to the breakers in the panel will be off—including the lower breakers.
The next picture is of a split bus panel with the cover off. Notice how much it looks like the sub-panel picture (well, except for tidiness)?
What is different about the panels can be visualized by the photo on the next page with color overlays.

The larger, blue-dotted lines are where the power coming into the panel attaches to the bus bars. Note that the top six double pole breaker spaces are outlined with smaller blue dotted lines and are numbered one through six. The wires from breaker #2 travel down behind the six spaces and attach (trust me) to the bars for the bottom breakers highlighted in red. Notice also that some of the double pole breakers in the area labeled “Service Disconnects” have been changed to single pole breakers, violating the six disconnect rule. Violations like this are common with these panels when more circuits are desired because there just isn’t room in the bottom section of the panel for more breakers.

At right is another panel with only three double pole breakers in the top six spaces, but one of them has blue wires that run to the bus bars for the lower circuits.

In this case it only takes three breakers to shut off all the power in the panel—still well under the six disconnect rule.
These panels were common into the early ’70s, and I still find them often. Most panel manufacturers made such panels—and in many different versions. The code allowed this type of panel when all the power could be shut off with six disconnects or less, i.e. the six disconnect rule.
Inspectors and homeowners sometimes mistake these split-bus panels for sub-panels and incorrectly call for repairs to the way they are wired, or they wonder where the main breaker is. I don’t want to go into the differences between how service panels are wired differently from sub-panels, but just understand that they are wired very differently, and it is important for the home inspector to know these differences.
To recap:
In a typical split bus panel found in a residence there will be provision for six double pole breakers (or less)—one of which is the disconnect for all the breakers located below the six double pole breaker locations. Wires will run from that one breaker and be connected directly to the bus bars for the other section of breakers. (Bus bars are the energized metal bars that the circuit breakers connect to.)
These panels are often crowded and no longer have ample space to accommodate modern wiring requirements. Most of the time I find myself recommending to my buyers that they upgrade these panels. Often the service size itself is adequate for the home; the panel simply lacks the space to add new circuits. Replacing just the panel is almost always going to be cheaper than a whole new service to the home. Because all these panels are older, upgrading is a good idea even if additional room is not needed.
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