(1) "Standby charges" are defined for the purposes of this rule as charges different than those generally available for service under the utility's tariffs, imposed where utility service is either provided:

(a) only in the event of the nonavailability to the customer of any other form or source of energy from any supply, which other form of energy is predominately relied upon by the customer; or

(b) on a regular basis as the customer's predominate energy source but is subject to periodic partial or complete curtailment, at the customer's option, and replacement by another energy form or source.