Split Bus Electrical Panels—No Main Breaker.

Doesn’t the Electrical Service Panel HAVE to have a Main Disconnect Breaker?”

Main Breaker in Service Panel

Main Breaker

The simple answer to this question is, “No—Probably not.”

Because most electrical service panels are NOT installed by homeowners or “Uncle Harry,” it is actually pretty rare to find a main panel without a main disconnect.  There are a couple of ways where it might “appear” to be missing—but is in fact there after all.  My goal is to keep this post simple enough that most readers can understand what I am talking about.

Real estate agents and home owners need to 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 a means of shutting off all the power.

Being able to shut off all of 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 mobile homes, 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.  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 following picture is of a pretty close to correctly wired sub-panel.  As a Seattle Home Inspector I love finding panels this nicely wired.  This type of panel will not usually have a main disconnect—it will be located at the electrical service equipment—-typically where the meters are located.

Nicely Wired Sub-Panel

Nicely Wired Sub-Panel

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 6 throws to shut all the power off.

This type of Service Panel is called a Split-Bus Panel.

The following 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?

Split Bus Electrical Panel

Split Bus Electrical Panel

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 above (well except for neatness)?

Split Bus Electrical Service Panel

Split Bus Electrical Service Panel

What is different about the panels can be visualized by by the following picture with descriptive overlays.

Split Bus Electrical Service Panel

Split Bus Electrical Service Panel

The blue dotted lines are where the power coming into the panel attach to the bus bars.  Note that the top six double pole breaker spaces are outlined with blue dotted lines and are numbered 1 through 6.  Note how 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 6 throw rule.  Violations of this type are common with these panels as more circuits are desired and there just isn’t room in the panel for any more.

Here 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.

Split Bus Electrical Service Panel

Split Bus Electrical Service Panel

In this case it only takes three throws to shut off all the power in the panel—still well under the 6 throw rule.

These panels were common into the early 70′s and I still find them very often.  Most panel manufacturers made such panels—-and in many different versions.  The code allows for this type of panel as long as all the power can be shut-off in 6 throws or less—known as the “6-Throw 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 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 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 “6″ double pole breakers (or less)—one of which is the disconnect for all the breakers located below the 6 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.

 

Charles Buell, Seattle Home Inspector

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Comments

  1. Very helpful post. I’m curious, is it easier to add a sub panel underneath a split bus panel and rewire the house to that or just replace the old panel entirely? I am updating a house from the 40′s that appears to have had a few piecemeal updates here and there but nothing seems to have been done “right”. Lots of electrical tape, few proper junctions and willy-nilly outlets piggybacked to odd lines throughout the house.

    I am a student and cannot afford to hire an electrician. Updating this old house will be my part-time job over the next few years, and I hope to make a small profit from its sell.

    • Charles Buell says:

      Well of course one could add a sub-panel but in the end you will still have the old main panel with no main disconnect. Even with a new panel for the same size service you can generally get a panel with a main breaker that has more available spaces for circuits than the current split-bus has. I am assuming all work is being done under permits, so having to pull the meter to replace the whole panel should not be an issue.

      • Charles,

        I don’t see a main equipment grounding conductor coming in the sub panel to the lug on the grounding bar? There should be 4 conductors (2 hots,1 neutral,and 1 equipment grounding conductor) Correct?

        • Charles Buell says:

          Duncan, in this installation the metal conduit to the panel is the acting as the grounding conductor.

          • Charles,

            In response to my to previous reply,you said the metel conduit is acting as
            the grounding conductor in the subpanel. I don’t see a metal bonding bushing on the conduit to ground the subpanel enclosure? All I see is a gray fiber bushing which just screws on the threads of the conduit to protect the conductors. I still think you need a grounding conductor run back to the main panel which feeds the subpanel. If your using the metal conduit solely as a ground, what would happen if one or more of the fittings (couplings etc.)would come loose or disconnected being used as the ground path back to the service? Could cause a fire. I know for this reason,good practice tells me to run a grounding CONDUCTOR back to the source.

            regards,

            Duncan

          • Charles Buell says:

            Yes, and that is exactly why they do not allow it any more. The metal lock nut under the plastic bushing was considered adequate to connect the conduit to the box itself—continuity of the conduit was “usual” but difficult to “guarantee.” I have found them disconnected—but that is considered rare but due to the possibility we now want to see a ground wire inside the conduit.

  2. i have an old house that has no service disconnects just a meter base and a split bus pannel inside. theere is no main disconnect anywhere. the distribution pannel is inside. i want to upgtrade the dis pannel. do i have to add a pannel with disconnects or will the individual circuit breakers suffice

    • Charles Buell says:

      Carlos, I am not sure why you would want a nice new panel and not want a main disconnect? Am I reading you correctly? As far as I know, you have to have a single main disconnect in modern installations.

  3. Great Blog! My father and I were both convinced that my service panel was missing the main breaker, but I see that I have a Split Buss panel thanks to your blog. I purchased a home in MI without an inspection or seeing it in person. I inherited a box that is overlystuffed and even had wires connected directly into the front with the cover off! In the state of MI they require an electrical safety inspection on any home that has the electricity off for more than a year (mine has been off for 3 now). So I am preparing myself to clean up some of the obvious no, no’s and have the inspection. Hopefully, my nothern Mi inspector will be as knowledgeable and helpful as you seem to be. Keep up the good work! Wish you were in MI!

  4. Louis Mallet-Paret says:

    Great post! I was convinced my daughter’s “new” (1950′s) old house was missing the main breaker but now understand much better what’s going on with the split bus panel. One question though. What overcurrent device protects the incoming wiring from the meter to the panel? Our 1950′s house has 120/240 volt #4 AWG copper TW which I think is good for only 60 Amps. When I add up the breakers on the first half of the split it comes out to more than 60. I have not found any main breaker upstream of the panel but am wondering if there are fuses or something hidden in the sealed meter enclosure. Any comments would be greatly appreciated. Thanks!

    • Charles Buell says:

      Louis, regardless of whether there is a main breaker in the panel or a split-bus means of disconnecting the power there is no protection of the wire between the meter and the panel and why it has to be in conduit and a very short distance between the two. Also adding up the amperage of breakers is not really indicative of anything except as indicated by the data plate. #4AWG copper is good for 100amps typically. Have the panel evaluated by an electrician if you have concerns about it.

  5. Dear Louis,
    I’m rewiring a house to make it more EMF friendly
    ie no EMF’s.
    It was suggested to use split bus to separate the loads. Emf high loads and resistive loads.
    A few details please!
    I’m suffering from emf sensitivity.

    • Charles Buell says:

      Ann, I know of no scientific evidence to support that EMF’s are a problem related to residential wiring. A Split Bus panel is a type of panel and would likely not make a difference in any electrical conditions related to EMF’s that I am aware of. “Anecdotal” information can sometimes seem convincing but generally just confuses the issue.

  6. I live in a townhouse and the circuit breaker panel appears having no main breaker, where a square hole above the two columns of circuit breakers is labelled “Main” but it is really an empty hole covered by two plastic pieces. I guess the circuit breaker panel in my unit is of the type you described in this article, a sub-panel.

    The circuit breaker dedicated to the kitchen’s under-sink waste disposal seems out of service, no power is available on this line when this breaker is flicked on, and it won’t trip either. So I’d like to replace this circuit breaker with a new one. However, all I read on how to replace a circuit breaker recommend to “turn off the power at the main breaker”

    You mentioned in this article about sub-panel, ” This type of panel doesn’t “require” a main breaker”, should I interpret this as I can replace the faulty circuit breaker without bothering to find out where the main breaker outside my unit is? Or, I have to turn off the main breaker outside my unit, which I assume is inside a box at the end of the building and locked up, so I really have no direct access to unless through the power company.

    In the whole last paragraph I am only guessing the possibilities. I hope you’d give me some advice on what I could do in this situation. Thank you for your help in advance.

    • Charles Buell says:

      Tom, based on the questions you ask I must suggest that you contact an electrician to make these repairs for you.

  7. Joel Neff says:

    I have a split bus panel from pushmatic. Home was built here in Michigan in 1965. The main lines from the meter go into the top of the panel in side my one family home. The first two breakers are 30amp and then a 60 amp panel starts for home lighting. I’d like a 100 main put inline but, the electricians here say it’s just better to upgrade the panel. There is nothing wrong with this panel other then not having a main 100 amp breaker. I can’t see spending $1500. to $2500. on a new panel install. Any ideas on what I should do??

    Thanks Joe

    • Charles Buell says:

      Joel, besides the lack of a main breaker there are other reasons why you should be looking to upgrade the panel. If there is nothing wrong with the panel, as you say, other than missing a main breaker why not just leave it alone? There is nothing inherently wrong with a split-bus panel. The problems arise when you need more spaces for modern circuit requirements when remodeling. If the six throw rule cannot be maintained it is time to upgrade. There is often insufficient space in these older panels and often breakers have been double lugged. I think you are probably getting good advise to upgrade the panel. If you don’t have to upgrade the entire service you should be able to get just the panel changed out for under $1500.00—it certainly would not cost more than that in my market. It will cost you something to have a main breaker installed—just put that money toward a whole panel is my advice.

      • Joel Neff says:

        Thanks for that fast reply. I don’t need to add a breaker to the panel. To me, having a main breaker coming into the panel seemed smart. Maybe in the years to come i’ll think about a upgrade. Thanks again for your comment on this.

        Joe

  8. Kevin Murray says:

    Hi Charles,

    This article is the closest thing I could find that addresses our sub-panel problem.

    We just bought a 1941 house that seems to have had the electrical panel updated by the seller (or maybe his Uncle Harry!). There is no main shut-off, only a sub-panel installed with 4 circuits for the whole house. We’re looking to have a 200-amp main panel installed professionally and run some new circuits to key appliance outlets as we can afford to do so.

    We got a local recommendation from a trusted source here in L.A. and the electrician just gave us a quote. His plan is to leave the sub-panel as-is (cloth wiring and all) and only run any new circuits we’ve requested from the new main panel. I understand that this, in theory, should be fine but we had an earlier quote from our real estate agent’s contractor which included rewiring all of the circuits to the new panel (and for a good deal less).

    Is this just a matter of preference or is there a right way to do it?

    Thanks!
    Kevin

    • Charles Buell says:

      Kevin, it can be done either way most likely if I read you correctly. If you would like to email me privately so that you could show me some pictures I might be able to advise you more appropriately.

  9. Charles: I was supposed to get a new service panel installed today,but my electrician found that there’s a sewer drain line directly under the box. The old box is 13″ x 24″,& he says they’re no longer made.The panel is a split buss type. Any suggestions? There just isn’t any room for abigger one.We’re not looking to add anymore circuits-just a problem with the buss.

    • Charles Buell says:

      Roger, I am not sure I fully understand what you want to know. I don’t know why the electrician can’t install a new panel in place of the split-bus panel. Modern panels that size will typically accommodate a main disconnect and still have room for all the circuits. Feel free to call me if you want.

  10. I realize this is an older post but I hope you can help me figure something out.
    We recently had an electrician (a very young one) out to do some other work and after looking at our system he recommended upgrading our system to 200 amps to the tune of $6000. Doesn’t make sense as we haven’t had symptoms of a lack of ampage – no frequently tripped breakers, flickering lights or the like. Reported that we currently have 150 amp service. He also expressed concern that we had no main shutoff.
    I looked back at our home inspection report to see if this issue was mentioned. The inspection report states that we do have 200 amp service. So I’m looking at the service panel trying to figure out what is going on and I’m confused.
    We have a large panel with 42 receptacles – several of which are not used. At the top left of the panel (which I understand to be where the main shutoff should be) is a double breaker with 100 printed on it, however it is labeled “Heat”. There are 4 breakers below it in place 5,7,9,11- 2 single switches and one double switch with 60 printed on it – all labeled “Sub-Main”. On the right side there are also 3 other double switches with 50-range, 30 – water heater and 30 – dryer. The breakers on the bottom half are all single and mostly printed with 20 and 30.
    So could this possibly be one of these split bus systems and that’s why there is no main shutoff? And do I have 100, 150 or 200 amp service?
    Home built in 1978, all electric, a little over 1600 sqf.
    Thanks for any enlightenment you can give.

    • Charles Buell says:

      Jessica, this sounds very much consistent with a split bus panel. There are many factors that would come into play to determine whether it should be replaced or not. The needs of the home. The manufacturer. Is there space for more circuits, etc. If you send me a picture privately I will try to be of further assistance. On the panel legend it should tell you the panel rating (size). If that is missing it may also be on a legend inside the panel but I would not recommend you remove the dead front.

  11. I have a dual split bus or whatever panel… I am going to have a throw switch installed with a lock assembly between the meter and the panel so I can kill power in one throw. This will also prevent back feed of my generator. Any thoughts on this?

  12. Raymond Carbone says:

    Charles,

    According to your description, I seem to have a split bus panel in my 1959-built home. Since we have many trees in the area, I am sorry to say that loss of power is becoming more common and I would like to be able to plug in a portable 7KW run-rated generator to power the in-house well jet pump, gas fired hot water furnace, and 2 refrigerator/freezers. Can an interlock be installed on a split bus panel to guaranty that only one source of power is connected?

    If a panel interlock switch can not be installed, I can use extensions from the portable generator to power the refrigerators and furnace (a 110 plug is built into the control unit and the emergency switch can be thrown to off), however how can I provide emergency power to my 220V jet pump? There is a small power box installed next to the pump that contains (2) 15A glass fuses used to cut power to the pump.

    I would appreciate your thoughts and suggestions.

    Ray

    • Charles Buell says:

      Ray, I just inspected a 1959 house with a split bus panel :) I am pretty certain that you cannot put an interlock type generator interface on it. Consult with a licensed electrician however. Given the age of the panel you might want to consider upgrading than the work it would take to making the old one work.

  13. Raymond Carbone says:

    Thank you for your quick reply. I appreciate that an upgrade would be best but not an option at this time. If an interlock can not be installed on the split-bus panel, how can I apply generator power to my in-home 220v jet pump servicing my water well? As mentioned above, along with the circuit breaker on my split-bus panel, there is a small power box installed next to the pump that contains (2) 15A glass fuses. Would it be a good idea to install a 220v twist receptacle between the small power box and pump to apply emergency power? Although I would be eliminating the short cut-off of the local fuse box, I am depending on the generator’s circuit breaker for any short encountered on any of the other connections.

    Again, thank you for your article and response. It has been very helpful.

    • Charles Buell says:

      Ray, I am afraid you have gone beyond my pay grade :) These interfaces can be incredibly dangerous to workers down line of the service, so making sure these installations are done properly is critical. Consult with an electrician at this point. I will say though, that making an interface work (if it can be done) with this old system may be more expensive than simply upgrading the panel.

  14. From your description it seems I have a split bus electrical panel. One of my double pole breakers has been tripping frequently ( to my range) and makes a buzzing sound from time to time. I’m thinking it may need to be replaced. As there is no main shut off, would I need the power company to turn off my power first? Does it sound like a problem that replacing the breaker will resolve?

    • Charles Buell says:

      Shari, too many possibilities to diagnose from the information you give. Time to have an electrician check it out for you. The power company will not likely be necessary to change the breaker—just an electrician.

  15. Tom DeCamp says:

    Just looked at a home that my niece was thinking of buying to render an opinion on its condition. (I’ve been a residential carpenter for 30 years.) I couldn’t figure out why there was no main shut off breaker in the circuit breaker box. The box was rated at 125 amps but only had a 60 and 30 amp double pole breakers in the top 2 spots. It must have been a split bus panel as you so clearly explained on this webpage. Thanks for the very informative description of this type of panel that I never new existed.

  16. James Critcher says:

    I have a split- bus panel which is located under meter and sub-panel is in the house. One of the 100 amp breakers is tripping and I need to replace it. There is no main labeled, so if I cut all breakers off in panel under meter, will power to house and this box be off.

    • Charles Buell says:

      I can’t tell you anything based on the information given. Pictures might help, but an electrician might be your safest bet.

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