Stan A. from Boise. Idaho Power just energized our new warehouse service last month. 480V 3-phase, estimated load around 150kW peak. They installed 400:1 CTs and set the multiplier accordingly, but our actual usage is running about 80-90kW and the bills seem way too high for a Schedule 19 account. I think they over-spec'd the CTs. The load calculations showed we needed maybe 200:1 CTs max. Anyone dealt with utilities installing wrong CT ratios on new services? Do we have any recourse or are we stuck with the 400:1 setup?
New service install - wrong CTs from day one
Wendell T. from Billings. NorthWestern Energy did similar to us - way over-sized the CTs for our actual load. The problem is accuracy at low load factors. 400:1 CTs reading 80kW are only running at 20% of capacity, which reduces meter accuracy. You should be able to request different CTs if your load doesn't justify the 400:1 ratio. Utilities usually size CTs for 120-150% of expected peak load.
Randy Dawson here. Stan, this is more common than you'd think with new services. Utilities often over-size CTs as a safety margin, but it can hurt accuracy at lower loads. The key is your load study and actual usage data. If your peak load is consistently under 120kW, you have a legitimate case for 200:1 CTs instead of 400:1. Idaho Power should be willing to discuss this, especially if you can show 6-12 months of actual usage data. The CT change itself isn't expensive for them - it's mainly labor. Push back on this if your bills seem high relative to actual consumption.
Greg L. from Indianapolis. Had this fight with AES Indiana on a new manufacturing facility. They wanted 600:1 CTs for a 200kW estimated load. We pushed back with load calculations and they agreed to 300:1. The difference in billing accuracy was significant at our actual operating levels around 120-140kW. Don't let them over-engineer your metering setup.
Thanks for the advice. I've been tracking our actual peaks and we're hitting 95-105kW max, well under the 400:1 CT capacity. Idaho Power said they'll review but want 3 months of usage history first. The December bill was $4,200 which seems high for our actual consumption level on Schedule 19.
Janet K. from Cincinnati. Duke Energy has a formal process for CT ratio review on new services. You file a request with your account manager and they'll do a field assessment. The 3-month requirement is pretty standard - they want to see your actual load patterns before making changes.
Final update - Idaho Power agreed to change to 200:1 CTs after reviewing our December usage data. Peak load was only 98kW so the 400:1 setup was definitely oversized. They're scheduling the CT swap for early January and will adjust the December bill once the new multiplier is active. Sometimes persistence pays off.