Split Bus Electrical Panels
Is your electrical panel missing a single main disconnect? You may have a split bus panel. I see these type of panels frequently in town so I thought we would discuss what a split bus panel is.
History
These panels were commonly installed in the 60’s to early 70’s. However we learned quickly they are not the best style of panel to use as they can be easily modified to make them unsafe. The manufacturing of split bus panels was discontinued in the mid-80’s.
What is a Split Bus Panel
Split Bus panels have two sets of breakers on separate bus bars. Typically the top set of breakers, are ALL service disconnects (or main breakers). They all have to be turned to the off position to turn the power off to the panel. You will typically see 6 double block breakers together, one of them is usually labeled ‘Main Lights’. This breaker controls all the entire bottom half of the panel, which are light and receptacle circuits.
Why They Can Be Unsafe
All homes must have a means of shutting off the entire service power to the house. The National Electrical Code (NEC) says that this needs to be completed in 6 throws or less. These types of service panels often become overcrowded and can no longer accommodate our modern wiring needs, so the double block main breaks are traded out for individual circuits. This causes the home to have more than 6 throws to disconnect the power in case of emergency.
In addition, the split bus panels still in service are now 40-60 years old, many with original breakers. The Consumer Product Safety Commission estimates 30-40 years life span for a typical circuit breaker. Older breakers can malfunction by doing nothing, NOT cutting off the electricity when the need arises. For safety precautions it is a good idea to replace the original breakers with new ones.