Umair Gaines
A split bus panel is an electrical panel with two separate bus bars. The bus bars carry the electricity and hold the circuit breakers. These panels were typically installed in the 1950s to 1970s but were discontinued in the 1980s due to arising problems as technology improved and homes required more electricity. In a split bus panel, there is no main shut-off, and they are identified by looking in the middle for a split bus, with lugs buried between the breakers.
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What You'll Learn
Split bus panels have two bus bars
A split bus panel is an electrical panel with two separate bus bars. The bus bars are metal bars inside an electrical panel that carry electrical current and hold the circuit breakers. The top bus bar typically feeds electrical current to large appliances and holds 5-6 breakers, while the lower bus bar is responsible for general lighting and outlets in the home.
The split bus panel was designed without a main breaker, unlike modern panels. Instead, they have 2-pole breakers installed at the top of the upper bus section, labelled as service disconnects. The lower bus bar section is fed from a 2-pole circuit breaker in the upper bus bar section. This means that to disconnect the power to the lower bus bar section, all circuit breakers in the upper bus bar section must be switched off.
The National Electrical Code (NEC) requires that all power in the home must be able to be shut off with no more than six hand movements or by throwing no more than six breakers. This is known as the "rule of six". In a split bus panel, there is no main shut-off, so one of the six breakers is used to feed the lower bus bar electrical current. The breakers in the upper bus bar supply power to large appliances, while the lower bus bar holds breakers for general lighting in the home.
The split bus panel was born in 1965, as a result of a statement in the National Electric Code (NEC) which allowed for individual protection for lighting and appliance branch circuit panel boards. This rule was an exception to a previous rule that allowed no more than two main circuit breakers. In 1981, the NEC restricted the section allowing split-bus panels to "existing installations", meaning no new split bus panels could be installed after 1981.
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They were common in the 1950s to 1970s
Split bus panels were typically installed in the 1950s to 1970s. They were common during this period as they were a cost-effective alternative to regular electrical panels. Unlike modern electrical panels, split bus panels did not have a main breaker. Instead, they had multiple breakers, often labelled as "service disconnects", which controlled the power supply to the home. This design feature allowed homeowners to avoid the need for large, expensive main breakers.
During the 1950s to 1970s, when split bus panels were most popular, small appliances were not as prolific as they are today. As a result, most non-major loads in homes at the time were for lighting. This meant that a single breaker could be used to control lighting power, while other breakers could be dedicated to major appliances.
However, as technology improved and homes required more electricity to power additional appliances and devices, the circuitry began to exceed the capabilities of the split bus panels. This led to overloading, which caused overheating, arcing, and damage to homes. As a result, split bus panels were discontinued in the 1980s.
Today, most split bus panels that are still in use are anywhere from 40 to 70 years old and are at the end of their useful lives. They often need to be evaluated, repaired, or replaced to fit modern electrical needs and safety standards.
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They were discontinued due to rising electricity demands
A split bus panel is an electrical panel with two separate bus bars. The bus bars carry the electricity and hold the circuit breakers. These panels were typically installed in the 1950s to 1970s but were discontinued in the 1980s due to rising electricity demands.
In a split bus panel, there is no main shut-off. Instead, there are 5 large breakers supplying power to large appliances, then one that supplies electrical current for the rest of the home. According to the National Electrical Code, a maximum of six breakers or throws must be able to shut off the electrical power. However, some split bus panels had more than six throws, leading to overloading, overheating, arcing, and damage.
As technology improved and homes required more electricity, split bus panels needed more room to supply additional components and appliances. Electricians overloaded these panels by adding single-pole breakers to the top bus bar, causing further issues. Today, most split bus panels have been modified to meet modern electrical needs, but this has resulted in overloaded circuits and other problems.
While some consider split bus panels outdated and in need of an upgrade, others argue that they are not inherently dangerous. However, they may require replacement if newer appliances or additional circuits are needed. It is recommended to consult a licensed electrical company to ensure safe and code-compliant electrical service and panel replacement.
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They can cause overloaded circuits, overheating and arcing
A split bus panel is an electrical panel with two separate bus bars. The bus bars carry the electricity and hold the circuit breakers. The top bus bar feeds electrical current to the main circuit breakers, which supply power to major appliances. The lower bus bar supplies power to general lighting and outlets in the home.
Split bus panels were typically installed in the 1950s to 1970s. However, they were discontinued in the 1980s due to arising problems. As technology improved, homes required more electricity, and the panels needed more room to supply additional components and appliances. Electricians and handymen overloaded these panels by adding single-pole breakers to the top bus bar, causing overheating, arcing, and damage.
Overheating and arcing can occur when circuits that make up the panel become overloaded. Overheating can also occur where a circuit breaker connects to an electrical panel bus, potentially damaging the bus and the connection. This can make equipment unreliable and prone to failure.
Damaged circuit breakers may not trip when an excessive or dangerous current occurs, leading to overheating and possible arcing. Conditions around an electrical panel can contribute to possible arcing and influence its severity. Electrical panel wiring should never be exposed outside the box, and combustible materials should be kept away from the area.
Overfusing, or using too many fuses inside an electrical box, can also cause arcing. Fuses that blow or circuit breakers that trip frequently can indicate a possible arcing hazard. Other indicators include burn marks, a burning smell, or buzzing and cracking sounds.
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They are not inherently dangerous
A split bus panel is an electrical panel with two separate, non-connected bus bars. Bus bars are the metal bars inside an electrical panel that carry electrical current and hold the circuit breakers. A split bus panel will have a large breaker on the top bus bar that feeds power to the lower bus bar. The top bus bar typically feeds electrical current to large appliances and holds six breakers. The other, typically, holds breakers for general lighting in the home.
Split bus panels are not inherently dangerous. While they are no longer installed in homes, this is due to changing requirements and technology, not because they are unsafe. They were typically installed in the 1950s to 1970s but were discontinued by the 1980s as they could not keep up with the increased electricity demands of modern homes.
The main issue with split bus panels is that they are old. Most are at least 40 years old, and the average circuit breaker lasts 30-40 years. This means they are at the end of their useful lives and can malfunction, not tripping when they should. However, this is an issue with any electrical panel of the same age.
Another issue is that they do not have a single main breaker to shut off all the power. Instead, they can have up to six breakers that must be switched off to cut the power to the whole house. This could add a few seconds to the time it takes to shut off the power in an emergency. However, this is a minor issue, and one that is easy to prepare for.
While split bus panels are not inherently dangerous, they do need to be understood and maintained. It is recommended that a professional inspects your electrical panel if you have any concerns.
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Frequently asked questions
A split bus panel is an electrical panel with two separate bus bars. The bus bars carry the electricity and hold the circuit breakers.
The top bus bar feeds electrical current to the main circuit breakers, supplying power to major appliances. The second bus bar supplies power to general lighting and outlets in the home.
You can identify a split bus panel by looking in the middle for a split bus. There will be lugs wired to a breaker above buried between the breakers.
The "rule of six" states that a maximum of six breakers can be used to shut off the electrical power. Split bus panels do not have a main shut-off, so up to six breakers may be required to turn off the power.
Split bus panels are not inherently dangerous. However, they are likely to be at least 40 years old and may have been unprofessionally modified to fit modern electrical needs, causing overloaded circuits, overheating, arcing, and damage.
