Yuri P from Chicago, IL. ComEd territory. Found a billing error that I think might be systemic. My client is a large office building on Rate BES-H. ComEd applies multiple riders: the transmission services charge, the purchased electricity adjustment, the energy efficiency rider, and the environmental cost recovery rider. The tariff says each rider is calculated as a percentage of the base distribution charge. But when I reverse-engineer the bill math, the riders are being calculated sequentially — the first rider is applied to the base charge, the second rider is applied to the base charge PLUS the first rider, the third is applied to the base plus first and second riders, and so on. The riders are stacking instead of being applied independently to the base.
Rider stacking error — surcharges calculated on top of other surcharges
Yuri, rider stacking errors are one of the most technically complex billing issues and one of the hardest to detect. The difference between parallel application (each rider calculated independently on the base) and sequential application (each rider calculated on the running total) is usually small in percentage terms but significant in dollar terms on large accounts. How much is the stacking costing your client?
Randy, the stacking effect adds about 2.8% to the total rider charges. On a building with $14,000/month in base distribution charges and about $4,200/month in total riders, the stacking adds approximately $118/month. Not enormous on a single account. But if this is a billing system issue affecting all ComEd BES-H accounts, the total impact across their service territory could be millions.
Yuri, I have 3 clients on ComEd BES-H in Dallas — wait, those are Oncor. Never mind. But the concept is the same. How did you confirm the riders are stacking and not just rounding differently than you expected?
Marcus, I built a spreadsheet that calculates the bill two ways — parallel and sequential. The parallel calculation matches the tariff language exactly. The sequential calculation matches the actual bill amounts within pennies. The parallel calculation produces a total $118 less per month. That consistency across 24 months of bills rules out rounding. It is definitively sequential stacking.
Yuri, that is solid forensic work. I would present this to ComEd with the spreadsheet showing both calculation methods and the 24-month pattern. The consistency of the discrepancy proves it is a systematic billing system implementation, not a random error. ComEd engineering should be able to verify whether their system applies riders in parallel or sequential mode.
Walt, filed the dispute with the full spreadsheet analysis. ComEd assigned it to their rate engineering department. After 4 weeks they came back and confirmed the billing system applies riders sequentially. They said this was a design choice made during system implementation, not a bug. I responded that the tariff language says each rider shall be calculated as a percentage of base distribution charges — not as a percentage of base plus prior riders. The tariff language is unambiguous.
ComEd escalated to their legal department. After another 6 weeks of back and forth, they agreed the tariff language supports parallel calculation. They are crediting my client for 3 years of stacking overpayments — $4,248. And they are modifying the billing system to apply riders in parallel as the tariff specifies. The system change will affect every BES-H customer in their territory.
$4,248 on your client but a billing system change that affects every BES-H customer in ComEd territory. Yuri, you just fixed a systemic error that was probably overcharging thousands of commercial customers. That is the kind of impact that matters beyond the individual case.
The ComEd rate engineer told me off the record that the sequential stacking had been in the system since 2008 and nobody had ever questioned it. Five years of overcharging every BES-H customer by approximately 2.8% on their riders. On a territory with tens of thousands of commercial accounts, the total overbilling was probably in the tens of millions.
Yuri, this is why line-by-line bill verification matters. Most auditors would look at the riders, see they are in the right ballpark, and move on. You actually reverse-engineered the math and found a 2.8% systemic error. That level of detail is what separates good auditors from great ones.