NERC requires each Balancing Authority to perform tie line flow error checks using MWh meters associated with each tie line every how many hours?

The correct answer is that NERC requires Balancing Authorities to perform tie line flow error checks using MWh meters associated with each tie line every hour. This requirement is crucial for maintaining system reliability and ensuring that the actual flows on the tie lines are accurately reflected by the metered values. By conducting these checks every hour, Balancing Authorities can promptly identify and correct any discrepancies that may arise due to inaccuracies in metering equipment or communication errors.

Performing these checks helps in maintaining the integrity of the data used for balancing the system and aids in effective coordination between interconnected systems. The regular monitoring of tie line flows is essential to avoid potential issues that could impact both local and regional grid stability.