How To Look At A House

McGarry and Madsen's home inspection blog for buyers of  

site-built, mobile/manfuactured and modular homes

What is a bus stab in an electric panel?

Sunday, July 7, 2019

Most electric panels have two vertical bus bars. Each bus bar has bus stabs, also called “bus fingers” or “connector fingers,” that are bent out to receive breakers. Each one can serve two full-size breakers, connected from left and right. In the example shown above, stabs #1 and #3 are part of the right bus bar. Stab #2 is connected to the left bus bar, and they alternate left and right as it goes down the pair of bus bars. 

    Many manufacturers specify a maximum total amperage allowed to be connected to one stab. So, for example, if a panel is rated for maximum of 150 amps per stab, then a 100 amp breaker on both sides of the same stab would exceed the max rating, but two 60 amp breakers would not. According to the manufacturer Square D, “the restrictions are applied only when we must limit the total amperage to pass applicable UL heat rise tests.” Here’s an example of a rating below.

    A tandem breaker, also called a “half-high,” which allows two breakers to attach to one side of a stab in what would ordinarily be a single breaker slot, doubles the amount of circuits on a stab to four when used on both sides, and the total of all four must be under the rating max. To learn more about tandems, see our blog post What is a tandem circuit breaker?  And for info on a panel detail to keeps too many tandem breakers from being installed in a panel, go to What is a CTL breaker?

    Another situation where the maximum stab rating may come into play is when a panel is backfed, which is also why the two slots opposite a backfeed breaker are often unused. See our blog post What is a "backfeed" main breaker at an electric panel? for more on this.

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Here’s links to a collection of our other blog posts about ELECTRIC PANELS:

• What causes copper wires to turn green or black in an electric panel?  

• What is the maximum number of circuit breakers allowed in an electric panel?

• When should a corroded or damaged electric panel cabinet or disconnect box be replaced? 

• What is a tandem circuit breaker? 

• When did arc fault circuit interrupter (AFCI) breakers first become required?

• Can an electric panel be located in a closet? 

• Can an electric panel be located in a bathroom? 

• Can you add circuit breakers by different manufacturers to an electric panel if they fit?

• My circuit breaker won't reset. What's wrong?  

• What is a split bus electric panel?

• How do I identify a combination AFCI (CAFCI) circuit breaker? 

• What does a circuit breaker with a yellow or white test button indicate? 

• What is the maximum gap allowed between the front of a recessed electric panel box and the wall surface surrounding it? 

• What are the requirements for NM-cables entering an electric panel box?

• Why is a fuse box/panel an insurance problem for homebuyers? 

• Why is bundled wiring in an electric panel a defect?

• What is the difference between GFCI and AFCI circuit breakers? 

• Why are old electrical components not always "grandfathered" as acceptable by home inspectors?

• What happens when you press the "TEST" button on a circuit breaker in an electric panel?

• What is a Dual Function Circuit Interrupter (DFCI)? 

• What is the difference between a Combination Arc Fault Circuit Interrupter (CAFCI) and an Arc Fault Circuit Interrupter (AFCI) circuit breaker?  

• What is the difference between "grounded" and "grounding" electrical conductors? 

• What does it mean when a wire is "overstripped" at a circuit breaker?

• Why is an old fuse panel dangerous?  

• Who is the manufacturer of those "bad" electric panels?

• Why is the circuit breaker stuck in the middle? 

• What is a double tap at a circuit breaker?

• What is the right electric wire size for a circuit breaker in an electric panel?

• What is the life expectancy of a circuit breaker? 

• My circuit breaker won't reset. What's wrong? 

• Why do some breakers in my electric panel have a "TEST" button on them?

• What is the right size electric panel for a house? 

• What do I need to know about buying a whole house surge protector? 

What is the maximum allowed height of a circuit breaker (OCPD) above the floor?

• What is the maximum height you can mount an electric panel above the floor? 

• What is the code required clearance in front of an electric panel?

What is the main bonding jumper and where do it find it in an electric panel? 

   Visit our ELECTRIC PANELS page for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.

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