How To Look At A House
McGarry and Madsen's home inspection blog for buyers of
site-built, mobile/manufactured and modular homes
What is a backfeed main breaker at an electric panel?
Monday, July 8, 2019
An electric panel is backfed when the main breaker is mounted in the cluster of breakers on the branch bus, instead of being separate, vertical, and above or below the branch-circuit breakers. It is essentially providing power “backwards” into the distribution bus. The breaker is usually, but not always, in the upper left position, and required to be clearly marked as “MAIN BREAKER.” A backfeed main breaker must also be mechanically secured in place. The red tab at the breaker above is a rated securing device, and it will only be visible with the dead front removed.
One additional requirement for a backfed main breaker is that the “maximum amps per stab” does not exceed what the manufacturer allows. A stab is another name for a bus bar finger. This maximum is listed in the data plate. If you backfeed a panel with a 100-amp service breaker, and the maximum allowed by the manufacturer is 125 amps per stab, then the max you can install on the other side of the stab is 20 amps. This is why the slots opposite a backfeed main breaker are often blank. To learn more, see our blog post What is a "bus stab" in an electric panel?
- Is the main clearly marked as “MAIN BREAKER”?
- Has the breaker been mechanically secured in place?
- Does the sum of the amperages of the main breaker and the one beside it come to equal or less than the “maximum amps per stab” listed on the manufacturer’s data plate?
Even a electric panel with a regular main breaker may be backfed by a breaker below it that is used for connecting a generator to the panel for use during a power outage. There are specific safety requirements for this type of backfeed, and they are intended to eliminate the possiblity of the both the main breaker and the generator backfeed breaker are on the same time. See our blog post Why did my generator hookup get tagged as defective by the home inspector? for more.
• • • • • • • • • • • • • • • • • • • • • • •
Here’s links to a collection of our other blog posts about ELECTRIC PANELS:
of Blog Posts
Top 5 results given instantly.
Click on magnifying glass
for all search results.
Buying a home in North/Central Florida? for a team inspection by two FL-licensed contractors and inspectors. Over 8,500 inspections completed in 20+ years. In a hurry? We will get it done for you.