When a submetering proposal lands on your desk, the spec sheet is full of numbers like "Class 0.2" or "ANSI C12.20." Those labels decide whether your data is good enough to bill a tenant, claim an incentive, or defend an ESG report. Choosing the wrong accuracy class is one of the most common — and most expensive — mistakes in a metering project, because the meter and the current transformer (CT) each carry their own error, and those errors stack.

What "Accuracy Class" Actually Means

An accuracy class is the maximum permissible measurement error a device may have under defined operating conditions, expressed as a percentage of the true value. A Class 0.5 device is accurate to within plus or minus 0.5 percent; a Class 0.2 device is accurate to within plus or minus 0.2 percent. Lower number, tighter accuracy, higher cost.

The Meter Standard — ANSI C12.20

In North America, revenue-grade electricity meters are governed by ANSI C12.20, which defines accuracy classes of 0.1, 0.2, and 0.5 — corresponding to within plus or minus 0.1, 0.2, and 0.5 percent of true value. "Revenue-grade" generally means a meter meets C12.20 (commonly Class 0.5 or better) and is therefore trusted for billing. If you intend to bill tenants or participate in utility programs, revenue-grade is usually the floor, not a luxury.

The CT Standard — IEC 61869 (and the Stack-Up Problem)

The meter only sees what the CT sends it. CTs carry their own classes — commonly 0.2, 0.5, and 1.0 — under standards such as IEC 61869-2. Here is the trap: a perfect meter fed by a mediocre CT produces mediocre data. Errors combine. Pairing a Class 0.5 meter with a Class 1.0 CT can yield a combined error of roughly plus or minus 1.5 percent at that point. To claim revenue-grade performance end to end, the CT must be matched to the meter, not just the meter chosen in isolation.

How Much Accuracy Do You Actually Need?

Match the class to the use case. For tenant billing, cost allocation, and incentive/rebate documentation, target a revenue-grade meter (C12.20 Class 0.5 or better) paired with a CT of equal or better class. For operational monitoring, load profiling, and fault detection — where you care about trends, not exact dollars — a Class 1.0 system is often perfectly adequate and meaningfully cheaper. Buying revenue-grade accuracy for purely operational dashboards wastes budget; using operational-grade accuracy for billing invites disputes.

Solid-Core vs. Split-Core CTs

Split-core CTs clamp around an existing conductor without a shutdown, which makes retrofits painless — but they typically carry a lower accuracy class and are more sensitive to installation error (gapped cores, off-center conductors). Solid-core CTs are generally more accurate but require disconnecting the conductor to install. The right choice balances accuracy needs against whether you can take an outage.

Specification Checklist

When you write or review a metering spec, call out: the meter standard and class (e.g., ANSI C12.20 Class 0.5), the CT class (e.g., IEC 61869 Class 0.5), the combined system accuracy, the operating current range over which that accuracy holds, and whether split-core or solid-core CTs are required. Specifying the meter alone is not enough.

Accuracy class is not boilerplate — it is the difference between data you can bill on and data you can only guess with. Match the class to the job, match the CT to the meter, and verify the combined system accuracy before you buy.