Electric panel buses colored red, blue, and black are indicative of what type of supply?

• A. 120-volt only supply
• B. 120/240-volt panels
• C. 3-phase supply
• D. 4-phase supply

Answer: (C)

Electric panel buses that are colored red, blue, and black indicate a 3-phase supply. In electrical systems, it is standard to use these colors to designate the different phases in a 3-phase electrical distribution system. Each color represents one of the three phases, which are essential for delivering power more efficiently, especially for larger loads.

A 3-phase supply is capable of providing a more balanced load across the system compared to single-phase systems. This is particularly important in commercial and industrial applications where large amounts of power are required, but it can also be utilized in residential settings for large appliances that necessitate higher power levels.

The other choices do not apply because a 120-volt only supply would typically use different colors, such as black for hot and white for neutral. A 120/240-volt panel could also feature different color coding, usually focusing on two phases rather than three. As for a 4-phase supply, it's not a standard categorization in residential or commercial power distribution, further supporting that the correct identification here aligns with the 3-phase system.