A Comprehensive Guide Single and Three Phase sub-metering.
Published on: August 21, 2023


With the increasing emphasis on energy efficiency and accountability in commercial office buildings, complying with regulations like Local Law 88 has become essential. The EASTRON MODEL SDM630 is a versatile sub-metering solution that offers accurate energy measurement for various applications. In this technical guide, we’ll walk you through the installation process of the SDM630 to ensure compliance with Local Law 88. Additionally, we’ll explore how to network multiple devices using Modbus hubs and internet gateways.

Before we begin, lets discuss the difference between three phase and single phase electric power.

3 Phase vs Single Phase Electric Loads

Single-Phase Electric Power:

Imagine a single water pipe delivering water to your home. This pipe provides all the water you need for things like drinking, cooking, and cleaning. Similarly, single-phase electric power is like having one “pipe” of electricity that powers your home or small businesses. It’s great for everyday uses like turning on lights, using appliances, and charging devices.

Three-Phase Electrical Loads:

Imagine you have three different water pipes carrying water to power different things, like lights, machines, and computers. These pipes work together in a balanced way, making sure there’s a continuous flow of power. Similarly, in a three-phase electrical system, there are three “pipes” of electricity that power various devices, making the overall distribution of power smoother and more efficient.

Now to make things a tiny bit more interesting, there are two types of three-phase electric loads and they are called 3-wire and 4-wire systems.

To clarify the contrast between 3-wire and 4-wire electric systems and why it is important for sub-metering purposes, let’s break it down:

3-Wire Electric System:

Think of a 3-wire system like a simple path for electricity to travel. It’s like walking on a trail with three clear directions to go. In this setup, there are three wires that carry electricity: one for the power to flow in, one for the power to flow out, and one that’s like a helper to keep things balanced. For sub-metering purposes we only need to sub-meter two of the three wires.

4-Wire Electric System:

If it uses power, we can sub-meter it.

Imagine you’re in a bigger place, like a neighborhood, and you need more paths to get around. A 4-wire system is a bit like that. It has four paths for electricity. In this case, you have the same three paths as before, but there’s an extra one added, like a special lane for certain things. For sub-metering purposes, we need to sub-meter 3 of the four wires.

The Difference between 3-wire and 4-wire three-phase systems in a nutshell…

In a 3-wire system, it’s like having a simple way for electricity to go back and forth. It’s used in many homes for regular things like turning on lights and using appliances.

In a 4-wire system, that extra path (the fourth wire) is there to handle something special, like bigger appliances that need extra power. It helps keep things safe and makes sure those big machines can work properly without causing any problems.

So, to put it simply, a 3-wire system is like a straightforward path for electricity, while a 4-wire system is like having a little extra road to handle bigger stuff in a safe and organized way.

Measuring kW Demand of a 3-Phase Electric Load:

Think of your home’s electricity meter. It keeps track of how much electricity you use in kilowatt-hours (kWh). But what about when many things turn on at the same time, like when you start the washing machine, turn on the lights, and use the oven? This sudden increase in power use is known as the “demand.”

For three-phase loads, it’s like having three sets of appliances running at the same time. To measure the demand, you need to know how quickly power is being used, which is where kilowatts (kW) come in.

Imagine you’re filling a bucket with water. The rate at which the water fills the bucket is like the rate at which power is being used. This rate is measured in kilowatts (kW). If you’re filling the bucket faster, it means you’re using more water per second, just like using more power per second in electrical terms.

To measure the kW demand of a three-phase electric load, you need a special meter that keeps track of how much power is being used at any given moment. This meter calculates the kW demand based on how much electricity is flowing through each of the three “pipes” of power.

When you use a lot of power in a short amount of time, like when you start many machines together, the meter notices the increase and records the higher demand. This helps businesses understand when they use the most electricity and manage their energy use more efficiently.

So, just like keeping an eye on how much water you’re using, measuring the kW demand of a three-phase electrical load helps manage and control power consumption in a more balanced and cost-effective way.


The Difference between Three Phase and Single Phase Power

The main difference is in how much power they can handle and what they’re used for:

  • Single-Phase: Think of single-phase like the standard water pipe in your home. It’s perfect for everyday needs and smaller devices. It’s like the electricity you use at home for your lights, TV, and kitchen appliances.
  • Three-Phase: Three-phase is like having those three water pipes. It’s designed for bigger tasks that need a lot of power, such as factories running machines, air conditioners in large buildings, and big industrial equipment. It’s like the supercharged version of electricity that can handle heavy-duty work.

In simple terms, single-phase is like a regular car that you use for daily commuting, and three-phase is like a heavy-duty truck that’s meant for hauling big loads. So, depending on what you’re powering, you might need the regular “car” power of single-phase or the heavy-duty “truck” power of three-phase.

Prerequisites for Installing Your kW Sub-meter

Before starting the installation process, make sure you have the following:

  1. EASTRON MODEL SDM630 submeters for each area to be monitored.
  2. Modbus communication cables.
  3. Modbus hub or gateway device (if networking multiple devices).
  4. Internet gateway (optional for remote monitoring).
  5. Tools including screwdrivers, pliers, and wire strippers.

Installation Steps

  1. Determine Installation Points:
    Identify the areas within the commercial office building that require submetering, such as individual floors, sections, or specific equipment.
  2. Mounting the SDM630:
    Install the SDM630 in an easily accessible location, such as an electrical panel. Mount it securely using appropriate hardware.
  3. Connect Wiring:
  • Turn off the power to the panel.
  • Connect the appropriate voltage and current wires to the SDM630’s input terminals, following the labeling on the device.
Example of Single Phase Wiring

Most tenant sub-meters are single phase wiring connecting office equipment and lighting systems. The diagram below illustrates how technicians should wire the SDM630 for single phase kW metering. Readers can access a link to this diagram on the store’s website by clicking here.

For 3 phase electric loads, there are 3-wire and 4-wire systems which have some nuances to address when installing kW sub-metering on them.

Configuring the SDM630 for sub-metering:

  • Access the SDM630’s setup interface via its display or software.
  • Set the device’s parameters, such as voltage and current values, communication settings (Modbus address), and CT ratio.

Modbus Networking If you’re monitoring multiple SDM630 devices:

  • Modbus Hub/Gateway Installation:
    • Connect each SDM630 to the Modbus hub/gateway using Modbus communication cables.
    • Set unique Modbus addresses for each device.
    • Configure the hub/gateway to poll data from each device.
  • Internet Gateway Setup (Optional):
    • Connect the Modbus hub/gateway to an internet gateway device.
    • Configure the internet gateway to send data to a remote monitoring platform.
    • This allows real-time data access and analysis from anywhere.

Testing and Calibration

  • After the installation is completed, proceed to power on the submeter(s) and check the display for accurate measurements.
  • Technicians should test the Modbus communication between devices to ensure the devices are transmitting data correctly.
  • Calibrate the SDM630 if necessary to ensure accurate energy measurement.

Data Monitoring and Compliance Reporting

Benefits of Sub-metering Using LC Associates’ Green Connect System

Utilizing Modbus communication to network multiple SDM630 devices offers several benefits:

  1. Centralized Data: Collect energy consumption data from various submeters in a centralized manner for comprehensive analysis.
  2. Efficiency Insights: By identifying energy consumption patterns, pinpointing peak usage hours, and recognizing areas of improvement, you can enhance energy efficiency.
  3. Real-Time Monitoring: Building Staff can access real-time energy data remotely through internet gateways to detect abnomalities. Detection of abnomalities requires swift action. Real-time data empowers swift action.
  4. Simplified Compliance: Streamline compliance reporting by consolidating energy data from multiple sources.
Tenant sub-metering for local law 88


The EASTRON MODEL SDM630 provides an effective solution for sub-metering applications in commercial office buildings. LC Associates helps you comply with Local Law 88 and improve energy efficiency. By following the installation steps outlined in this guide and utilizing Modbus networking with hubs and internet gateways, you can accurately monitor energy consumption and contribute to a more sustainable built environment.

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