How Does Electrical Submetering Work in Multitenant Buildings?

Electrical submetering uses revenue-grade meters with current transformers installed on individual tenant feeders, downstream of the utility's main meter, to measure each tenant's electricity consumption separately. The design package places the meters in the electrical distribution, sizes the CTs to the feeder loads, provides communication wiring for data collection, and documents compliance with NEC metering provisions and applicable energy-code monitoring requirements. The business case is simple: without submeters, the landlord either eats the utility bill or splits it by square footage, and neither is fair. Square-foot allocation punishes efficient tenants and subsidizes heavy users, and it gives nobody any reason to conserve. With submeters, each tenant pays for what they use, the landlord recovers real costs, and the building gains the granular consumption data that makes energy management possible. In California, that data is not just nice to have — the 2025 California Energy Code (2025 Standards), effective January 1, 2026, requires energy monitoring on covered commercial buildings, and the submeter design is how that requirement gets satisfied in practice.

The design starts on the one-line diagram: every submeter location shown in the distribution hierarchy, from the service entrance down through the tenant panels, so the metering architecture is legible to the plan checker, the contractor, and the future facility manager. Each meter gets a CT specification — ratio, accuracy class, window size, and whether it is solid-core for new construction or split-core for retrofit — matched to the feeder it monitors. Undersized CTs saturate and read wrong; oversized CTs lose low-end accuracy. Getting the ratio right is the core of the design. Then comes the communication layer, which is where most submetering projects quietly fail. A meter that nobody reads is a very expensive panel decoration. The design specifies how the data gets out — hardwired RS-485, Ethernet, or an approved wireless path — and where it lands: a building management head-end, a cloud dashboard, or a simple local readout. Panel schedules get updated to show the metering, conduit and box layouts are drawn where new raceway is needed, and the energy-code compliance documentation ties the monitoring points to the code sections that require them. The deliverable is a package a contractor can build and an owner can actually use, not a box of parts and a hope.

The tenant count is the obvious driver — forty submeters is more design and more hardware than four — but the subtler drivers decide whether the project goes smoothly. New construction is clean: meters and CTs go in with the gear, raceway is in the slab or the walls, and everything is coordinated on paper first. Retrofits add field investigation, working around energized equipment, and the reality that older panels may not have room for CTs and meters without creative solutions. The billing question deserves more weight than it usually gets. If the meters will support tenant billing, the design has to be defensible: documented CT ratios, a stated accuracy class, and commissioning records showing each meter was verified against a known load. The first time a tenant disputes a bill, that documentation is the difference between a five-minute conversation and a legal headache. Data ownership is the other overlooked scope item — who hosts the metering data, who can see it, and what happens when the building changes management companies. We define that in the design narrative so it is decided deliberately rather than discovered later. If you are scoping a submetering project, decide the data question first: who reads the meters, how, and what gets done with the numbers. The hardware is the easy part.

• Meter and tenant count: each additional submeter adds hardware, design, and commissioning
• New construction vs. retrofit: retrofits need field surveys and workarounds for existing gear
• CT sizing and type: solid-core for new work, split-core for retrofit, each with space and accuracy tradeoffs
• Communication architecture: hardwired, wireless, or cloud — the data path is half the project
• Energy code monitoring: 2025 California Energy Code requirements define minimum monitoring scope
• Billing-grade accuracy: ANSI C12.20-class metering and documented CT ratios for defensible tenant billing