Chris D. Memphis TN. Interesting case here - client had equipment failure that caused one phase of their 480V service to go down for about two weeks before they caught it. MLGW bills showed demand dropped by exactly one-third during that period. Got me thinking about how CT multiplier errors might be masked if you lose a phase and don't realize it. Anyone seen situations where partial phase loss made multiplier errors less obvious?
Three Phase Meter with Dead Phase Detection
Brenda J. Birmingham AL. Chris, Alabama Power had a similar case where lightning damaged one phase CT and it took months to figure out why the bills looked weird. The problem is when you lose readings from one phase, the billing can get really screwy. Some meters estimate the missing phase, others just bill on two phases. Makes it hard to spot other metering errors.
Randall O. Kansas City MO. We had a client where Evergy's CT on B-phase went bad and they were billing estimated reads on that phase for six months. Meanwhile they also had the wrong multiplier on C-phase. By the time everything got sorted out the billing adjustments were incredibly complex. The utility had to bring in their senior metering engineer to unravel it all.
Randy Dawson here. This is a great point Chris. Phase loss or CT failures can definitely mask multiplier errors because the load patterns become erratic and unpredictable. The key is always monitoring your power factor and load balance across phases. If you see sudden changes in demand patterns or power factor, check for both equipment issues and metering errors simultaneously. Many utilities' AMI systems should flag phase loss conditions, but not all of them do it reliably.
Calvin B. Memphis TN. Randy makes a good point about monitoring power factor. We use that as an early warning system for both equipment problems and metering issues. When PF suddenly changes without explanation it usually means something went wrong - either with the load or the metering. Chris, did your client notice any equipment problems during that two week period?
Calvin, they didn't notice because the failed phase was feeding mostly lighting loads and they just thought some circuits were out. The main production equipment was on the other two phases so operations continued normally. Only caught it when MLGW bill showed the demand drop. Made me realize how easy it would be to miss a CT multiplier error if you had intermittent phase issues.
Vera C. Olympia WA. This thread is really helpful. Puget Sound Energy had a case where a tree branch was intermittently hitting one phase of the overhead service. Caused random power quality issues for months. During that same period they also had a wrong CT multiplier but the erratic load patterns made it impossible to spot until they fixed the tree problem. Sometimes you have to solve the obvious problems first.
Patty K. Reno NV. Great discussion. NV Energy's newer AMI meters are supposed to flag phase imbalance and CT problems but we've found they don't always work as advertised. Still need to do the detective work manually. Chris, do you have any load monitoring equipment installed to catch these issues faster next time?
Patty, we installed a power monitor after this incident. Wish we had done it sooner. The monitor would have caught both the phase loss and probably helped us spot any CT multiplier errors too. Lesson learned - you can't rely solely on utility metering to catch problems. Need your own monitoring for critical loads.