For a building with only one circuit, such as a water well, what is the allowable service entrance capacity?

In the context of electrical installations for buildings that only have one circuit, the allowable service entrance capacity is typically designed to support the specific needs of that circuit while ensuring safety and compliance with electrical codes.

A capacity of 90 amperes is significant enough to handle common household electrical demands effectively while providing room for potential future requirements. A service entrance capacity of 90 amperes can safely accommodate most applications, including a water well, which may require a substantial amount of current to operate its pump efficiently.

The other options might not align with common electrical standards for such installations. For instance, a capacity of 70 amperes may be inadequate for certain water well systems, while 100 amperes could offer more capacity than necessary for a single circuit, potentially leading to inefficient use of resources and increased costs. The choice of a specific capacity is based on balancing safety, efficiency, and the expected load of the application involved.