Monitoring Sub-Panel Electrical Usage: A Step-By-Step Guide

Monitoring electrical usage in a sub-panel can be done in two ways. One way is to monitor the sub-panel feed from the main panel, which will give you the entire electricity usage for that sub-panel. The other way is to monitor the circuits within the sub-panel, which will provide a complete picture of electricity usage by the unit in the building. There are various devices and methods available to monitor electrical usage in a sub-panel, including current transformers (CTs), electricity meters, and web-based apps. Some devices use machine learning to identify individual appliances and their electricity usage, while others rely on owner interaction to identify loads. It is important to note that the cost of monitoring electricity usage in a sub-panel can vary, with projects starting at approximately $1500.

Current transformers (CTs)

CTs are a type of instrument transformer, which scales large values of voltage or current to small, standardised values that are easy to handle for measuring instruments and protective relays. They isolate measurement or protection circuits from the high voltage of the primary system.

A CT has a primary winding, a core, and a secondary winding. The alternating current in the primary produces an alternating magnetic field in the core, which then induces an alternating current in the secondary. The primary circuit is largely unaffected by the insertion of the CT. The current in the secondary is the current in the primary (assuming a single turn primary) divided by the number of turns of the secondary.

CTs are specified by their current ratio from primary to secondary. The rated secondary current is normally standardised at 1 or 5 amperes. For example, a 4000:5 CT secondary winding will supply an output current of 5 amperes when the primary winding current is 4000 amperes.

CTs are used for measuring current and monitoring the operation of the power grid. They are also used to monitor high currents or currents at high voltages.

There are different types of CTs, including:

• Bar type - the cable or bus-bar of the main circuit serves as the primary winding.
• Window type - there is a conductor opening in the core of the transformer to allow passing of a conductor that carries the current flow.
• Wound type - a primary wound coil carries the full load current.
• Split-core - either have a two-part core or a core with a removable section, allowing the transformer to be placed around a conductor without disconnecting it first.

Sub-metering options

There are two main options for monitoring electricity in sub-panels: monitoring the sub-panel feeds or monitoring the sub-panel circuits.

Monitoring the sub-panel feeds

This involves measuring the sub-panel from the main panel. Current transformers (CTs) are clamped around the wires connected to the sub-panel circuit and wired to an electricity meter. This method provides information on the energy consumption of the unit or area within a building connected to the sub-panel.

Monitoring the sub-panel circuits

This option involves monitoring all the circuits within the sub-panel to get a complete picture of electricity use by the unit in the building. This can be done using electricity meters or web-based apps.

There are a variety of sub-metering options available on the market, ranging from simple and cheap meters to more high-tech and expensive solutions. Some sources suggest purchasing used meters online, which can be significantly cheaper than new ones. There are also web-based apps, such as the one offered by PowerWise, that can provide detailed information on power and energy use, peak demand, and kilowatt hours (kWh) by hour, day, and month.

It is important to note that local regulations may restrict sub-metering and billing tenants for electricity use, so it is advisable to check with local authorities before installing a sub-meter for this purpose.

Energy management systems

There are two main options for monitoring electricity in sub-panels: monitoring the sub-panel feeds and monitoring the sub-panel circuits. The first option involves measuring the electricity usage of the sub-panel from the main panel. This can be done by using current transformers (CTs) that clamp around the wires connected to the sub-panel circuit and wiring them to an electricity meter. This method provides information on the overall energy consumption of the sub-panel.

The second option is to monitor each circuit within the sub-panel individually. This approach offers a more comprehensive understanding of electricity usage by providing data on the energy consumption of each circuit. This can be achieved by using sensors, meters, and apps specifically designed for energy management.

There are various tools available to help with energy management, ranging from basic electricity meters to more advanced smart apps. For example, PowerWise offers a web-based app that provides detailed energy usage reports, including power usage, peak demand, and kilowatt-hour consumption by hour, day, and month. Other options include the Sense Home Energy Monitor, which provides real-time insights into overall energy usage and individual device consumption, and the Efergy, a more affordable solution for basic energy monitoring.

By utilizing energy management systems, individuals and businesses can effectively monitor their electrical usage, identify opportunities for optimization, and make more informed decisions to reduce their energy costs and carbon footprint. These systems offer a range of features and price points to cater to different needs and budgets.

Apps and software

There are a variety of apps available that can be used in conjunction with energy monitors to provide real-time data on your electricity usage. These apps often come with the purchase of an energy monitor and can be downloaded onto your smartphone, offering a simple way to track your energy usage on the go. Some apps are also available for free if your electricity provider has installed a new Wi-Fi-enabled smart meter in your home.

The Sense app, for example, is a smart app that helps you take control of your home energy usage. It provides real-time insights into how much energy your home and individual devices are consuming, helping you identify opportunities to save money and reduce your carbon footprint. The app can be downloaded for free if your electricity provider has installed a new Wi-Fi-enabled smart meter, or you can purchase the Sense Home Energy Monitor to access the app.

Another example is the Emporia app, which can be used with the Emporia Gen 2 Vue monitor. This app offers integrations with various smart devices, such as smart plugs, thermostats, and lighting, to provide insights into their energy usage.

In addition to these apps, there are also web-based apps that can provide detailed energy usage reports. For example, PowerWise offers web-based apps that report on power and energy usage by a subpanel, showing when electricity is being used and what the peak demand is. These apps can provide a comprehensive overview of your energy usage, helping you make informed decisions about your electricity consumption.

When choosing an energy monitor and app combination, it is important to consider the compatibility with your electrical system, the accuracy of device identification, and the ease of installation. It is also worth noting that some apps may offer additional features, such as notifications for critical devices or the ability to track time-of-use rates.

Overall, the use of apps and software can be a powerful tool for monitoring your electrical usage, providing detailed insights that can help you save money and reduce your environmental impact.

Electricity meters

Current Transformers (CTs)

One common method is to use current transformers (CTs). CTs are clamped around the wires connected to the sub-panel circuit, and they measure the electricity flowing through those wires. These CTs are then wired to an electricity meter, which records the data. This approach is often used to monitor the entire electricity usage of a sub-panel and can be done from the main panel or within the sub-panel itself.

Smart Meters

Smart meters are an advanced type of electricity meter that provide more detailed data on electricity usage. They can be installed at the main panel or sub-panel level and offer features such as real-time monitoring, historical usage data, and the ability to track usage by individual circuits or devices. Smart meters often use machine learning to identify specific appliances and their electricity usage, providing a more granular understanding of energy consumption.

Web-Based Apps

In addition to hardware solutions, there are also web-based apps that can help monitor electricity usage. These apps provide visual representations of power usage, such as energy charts showing kilowatt-hours (kWh) by hour, day, and month. They can also show when electricity is being used and what the peak demand is, helping users identify patterns and areas for improvement.

Cost Considerations

It's important to consider the cost of implementing electricity metering for sub-panels. The equipment, including the electricity meter, gateway, current transformers, and software subscriptions, can start at around $1500. Additionally, the level of complexity and the number of circuits or devices being monitored can impact the overall cost.

In conclusion, electricity meters play a vital role in understanding and managing electrical usage, especially in sub-panels. By utilizing CTs, smart meters, web-based apps, or a combination of these tools, users can gain valuable insights into their energy consumption and make informed decisions to reduce costs and improve efficiency.

Frequently asked questions