Split on your Split Bus? Electrical Panels

Published by Don Hester on November 24, 2020November 24, 2020

There was a period of time that you will find electrical service panels that do not have a single main service disconnect on them.

By code it is required to have a means to disconnect the power to a building or home which can be a single breaker (or disconnect) or a group of breakers, fuses or disconnects as long as it does not exceed 6 of these grouped together. They need to be clearly labeled as “Main Disconnects”

Starting around the 1950’s a common service panel type was referred to as a Split-Bus. Where you had a grouping of up to 6 each 240 volt breakers that would qualify as your service disconnect.  One of the 240v breakers would feed all the other breakers below (lighting and other appliances circuits) while the remaining breakers would feed typically larger 240v circuits such as ranges, dryers, water heaters and furnaces.

The main reason for this design was cost. The larger main breakers (100-200 amps) of the time were very expensive and a way to reduce cost was to incorporate lower cost, lower amp rated breakers (Typically 60 amps or less).

The allowance of more than two disconnects in a panel (panelboard) for residential was by an exception to NEC 384.16 which required no more than two main circuit breakers or two sets of fuses. It was in the 1981 code that this exception was now only allowed in existing dwellings. 

1981NEC  (underline and highlight is mine)
384-16. Overcurrent Protection.

(a) Lighting and Appliance Branch-Circuit Panelboard Individually Protected.

Each lighting and appliance branch-circuit panelboard shall be individually protected on the supply side by not more than two main circuit breakers or two sets of fuses having a combined rating not greater than that of the panelboard.

Exception No. 1: Individual protection for a lighting and appliance panelboard shall not be required if the panelboard feeder has overcurrent protection not greater than that of the panelboard.

Exception No. 2: For existing installations, individual protection for lighting and appliance branch-circuit panelboards is not required where such panelboards are used as service equipment in supplying an individual residential occupancy.

Code text from pre 1981 NEC code that shows the exception to the Two Main Breaker or Fuse rule-

1978 – NEC  (underline and highlight is mine)

384-16. Overcurrent Protection.

(a) Lighting and Appliance Branch-Circuit Panelboard Individually Protected.

Each lighting and appliance branch-circuit panelboard shall be individually protected on the supply side by not more than two main circuit breakers or two sets of fuses having a combined rating not greater than that of the panelboard.

Exception No. 1: Individual protection for a lighting and appliance panelboard shall not be required if the panelboard feeder has overcurrent protection not greater than that of the panelboard.

Exception No. 2: Individual protection for lighting and appliance branch-circuit panelboards is not required where such panelboards are used as service equipment in supplying an individual residential occupancy.

So after 1981 this type of split bus panelboards was no longer allowed.

Also, in the photo we have a Zinsco brand electrical panel. These are older problematic panels are really should be replaced.

http://www.ncwhomeinspections.com/arcing+on+zinsco+panels

http://www.ncwhomeinspections.com/Zinsco+Panel+and+Breakers

If you find any errors or have additional information that would expand on any code, building standards or manufacturer requirements please let me know.

NCW Home Inspections, LLC  is a Licensed Washington State Home Inspection service located in Wenatchee Washington serving Chelan County, Douglas County, Kittitas County, Okanogan County and Grant County Washington and the cities of Wenatchee, Leavenworth, Cashmere, Oroville, Cle Elum, East Wenatchee, Quincy and many more…  

Your Wenatchee and Chelan Professional Real Estate, Home and Structural Pest Inspection Service

Coordinator & Instructor- Fundamentals of Home Inspection-  Bellingham Technical College

Former WA Home Inspector Advisory Licensing Board

www.ncwhomeinspections.com                                                   509-670-9572

 You can follow me on Facebook, Twitter, Google+ and on my website Blog.

If you find any errors or have additional information that would expand on any code, building standards or manufacturer requirements please let me know.

NCW Home Inspections, LLC  is a Licensed Washington State Home Inspection service located in Wenatchee Washington serving Chelan County, Douglas County, Kittitas County, Okanogan County and Grant County Washington and the cities of Wenatchee, Leavenworth, Cashmere, Oroville, Cle Elum, East Wenatchee, Quincy and many more…  

Your Wenatchee and Chelan Professional Real Estate, Home and Structural Pest Inspection Service

Coordinator & Instructor- Fundamentals of Home Inspection-  Bellingham Technical College

Former WA Home Inspector Advisory Licensing Board

www.ncwhomeinspections.com                                                   509-670-9572

 You can follow me on Facebook, Twitter, Google+ and on my website Blog.

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