A BA that is part of a multiple BA Interconnection and not receiving Overlap Regulation Service must maintain a B that is:

In the context of balancing authority (BA) operations within a multiple BA interconnection, it is important for each BA to maintain specific parameters to ensure stability and reliability in frequency regulation.

The requirement that a BA maintain a balance (B) is crucial when it is not receiving Overlap Regulation Service. A balance less than zero signifies that the BA is not generating enough to meet its load, which could either be a condition of the market or a strategic decision based on operational parameters.

Furthermore, the stipulation that the balance must be equal to or more negative than its Frequency Response Obligation (FRO) when frequency deviates from the nominal 60 Hz by more than +/- 0.036 Hz aligns with regulatory requirements. This ensures that when frequency disturbances occur, the BA has sufficient capability (or is in a position of negative balance) to respond and stabilize the system in conjunction with other BAs.

Combining both of these points solidifies the fact that maintaining a balance less than zero at all times, along with adherence to the FRO requirement under frequency deviations, is essential for the overall stability of the interconnection. Hence, the correct answer encompasses both criteria as necessary conditions for the BA's operational compliance in this scenario.