Feeling a little embarrassed asking this but I keep seeing references to meter multipliers and CT ratios and I want to make sure I actually understand the mechanics before I start checking these on client accounts. Can someone break it down simply? I get that large commercial meters use current transformers but I am fuzzy on how the multiplier gets applied to the billing.
What exactly is a meter multiplier?
No need to be embarrassed, this trips up a lot of people. Here is the short version: large commercial accounts use more power than a standard meter can measure directly. So they install current transformers (CTs) that step the current down by a known ratio — say 200:5, which is a 40:1 ratio. The meter reads 1/40th of the actual usage, and then the billing system multiplies the meter reading by 40 to get the real consumption. That multiplier is literally just the CT ratio. The problem arises when the physical CT ratio and the billing multiplier do not match. If the CTs are 200:5 (multiply by 40) but the billing system has a multiplier of 20, the customer gets billed for half their actual usage. If it is set to 80, they get billed double.
OK that makes a lot more sense now. So when I am auditing, where do I find the installed CT ratio vs what the utility is using for the multiplier?
Request the meter installation record from the utility — it should show the CT specs, VT specs if applicable, and the programmed multiplier. Then compare that to what shows on the actual bills. Most bills will show a multiplier or a meter constant somewhere, though some utilities bury it. Idaho Power puts it right on the bill header. Some utilities you have to ask for it specifically.