SCE customer in Santa Clarita had one phase go dead on their three-phase service about 6 months ago. Customer didn't notice because they have mostly single-phase loads that kept working on the other two phases. Meter kept registering but at about 65% of actual usage. Customer's bill dropped significantly but they just thought it was due to some efficiency improvements they made. How common is this type of issue and how quickly should AMI systems detect it? Gordon C.
Three Phase Meter With Dead Phase - How Long Undetected?
Gordon C., this is more common than you'd think. NV Energy had a similar case here in Las Vegas where customer went 8 months with one dead phase. Modern AMI systems should flag voltage imbalances but many utilities don't have alerts configured properly. The customer got hit with a substantial back-bill when it was finally discovered during a routine inspection. Kim S.
We see dead phase issues regularly in Dayton with AES Ohio. Usually caused by loose connections or blown fuses at the transformer. AMI meters can detect this if the utility has phase monitoring enabled, but many don't use that feature. Customer should document when the phase went dead to limit any back-billing exposure. Irene D.
Gordon C., dead phase conditions should trigger alarms in properly configured AMI systems, but many utilities focus on outage detection rather than power quality monitoring. The billing impact depends on the customer's load mix - predominantly single-phase loads will show less impact than balanced three-phase motors. Document the timeline carefully and check if customer equipment showed any performance issues that could establish when the problem started. Utilities typically can back-bill for the full period of under-registration. Randy D.
Had exact same situation with PG&E customer in Santa Rosa. Dead phase for 4 months, bills dropped 30%. PG&E's AMI system did detect the voltage imbalance but the alert got buried in their system and nobody acted on it. Customer ended up with $12K back-bill. Now I always recommend customers monitor their own power quality with independent meters. Iris W.
Check if any three-phase equipment started running hot or showing performance issues. That can help establish timeline for when phase went dead. Duke Energy in Charlotte had a case where customer's HVAC system logged fault codes that proved when the problem started, which limited the back-billing period. Derek O.
Good point Derek O. Customer's facilities team did notice some motor issues about 5 months ago but didn't connect it to the electrical service. SCE is saying they want to back-bill for 6 months but we're pushing back with the equipment performance data. Still negotiating but looks like we can limit it to 4-5 months max. Gordon C.
This is why I always recommend quarterly power quality monitoring for three-phase customers. NorthWestern Energy here in Billings had multiple cases last year where customers went months with dead phases. Simple data logger would have caught it immediately. Prevention is cheaper than back-billing disputes. Wendell T.