Weird situation with Xcel Energy three-phase service. Client reported equipment issues and we found one phase completely dead - no voltage. But meter is still registering about 60% of normal usage. How is this possible with dead phase? CTs are 200:5 on all three phases. Steven D.
Three Phase Service with Dead Phase - Meter Still Reading?
Steven - Few possibilities here. Could be CT wiring issue where the dead phase CT is actually reading current from one of the live phases. Also possible the load is redistributing to the two good phases. What type of load is this and have you verified the CT wiring? Randy D.
Load is mostly three-phase motors for manufacturing equipment. Some of the motors are single-phase though. Haven't checked CT wiring yet - good point. Could a miswired CT cause this? Steven D.
Definitely check CT wiring first. We found a case where installer crossed the CT leads and one phase was reading current from another phase. Made troubleshooting a nightmare until we figured it out. Norm R.
Also verify that phase is actually dead and not just low voltage. Sometimes what looks like dead phase is actually severe voltage imbalance. Seen this on older services with corroded connections. Kira J.
Checked with client's electrician - phase A is definitely dead, zero volts to neutral and to other phases. Going to have them check the CT wiring tomorrow. This is on Schedule SG rate with TOU periods. Steven D.
Had similar issue with KU service in Lexington. Turned out the "dead" phase wasn't actually dead at the meter - problem was downstream in customer's panel. Meter saw all three phases fine. Worth checking voltage at meter location. Oz F.
Update: Problem was CT wiring. Phase A CT secondary was connected to Phase B terminals in meter. So meter thought it was reading Phase A but actually reading Phase B current twice. Explains the weird readings. Steven D.
Good detective work Steven. CT miswiring is more common than people think, especially on new installations or after maintenance. Always worth checking when readings don't make sense with the electrical situation. Randy D.
How long was this running with wrong wiring? Any billing impact or was it just confusing readings? Dave T.
Been like this since installation about 8 months ago. Billing was actually pretty close to correct because total current was still being measured, just attributed to wrong phases. No back billing needed thankfully. Steven D.
Lucky break on the billing. We had similar wiring issue with National Grid that caused 6 months of overbilling because the crossed CTs made it look like higher demand. Carl H.