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Can Your Overload Relay Reduce Your Electric Bill?

The energy consumed by electric motors in a manufacturing facility is one of the main contributors to the total electrical cost for manufacturers. Large manufacturing facilities with many electric motors often use networked based electronic overload relays to protect their electric motor investment, control the motor in a distributed manner with its integrated I/O features, and monitor motor health information to prevent unplanned down time.

However, many manufacturers do not realize that these same electronic overload relays provide some form of power based diagnostic information that can provide a manufacturing facility with insightful information about how to efficiently use electrical energy and lower their overall electric costs.

The electric bill for most manufacturing facilities is made up of three components:

  • Energy Consumption (kWh) 50-70%
  • Demand (kW Demand) 25-50%
  • Efficiency (Power Factor) 5-10%

Energy consumption rates are based on the time of day, the day of the week, and the month of the year. Demand rates are typically based on the maximum 15 minute window of energy usage for the month and sometimes for the year. Most manufacturing facilities do not fully understand why they are being charged for each line item on their complicated monthly electric bill, so they just blindly pay it.

By historically logging electrical usage at the utility feed and comparing it to the individual electrical loads at a facility, a manufacturing facility can gain invaluable knowledge about how they consume electrical energy. This information can be used to better manage their energy usage and save 10-50% on their electrical costs.

If network based electronic overload relays already exist in a facility, they can also be used to monitor energy usage at the individual motor loads. Using a historical data collection system, users can monitor current usage (at a minimum) for the respective electric motor that the overload is protecting.

Some electronic overload relays will also provide power values (kW, kVAR, kVA, and PF), energy values (kWh, kVARh, and kVAh), and demand values (kW, kVAR, and kVA). This data should be collected at a minimum of 15 minute intervals. Software packages can collect historical energy data from electronic overload relays and power monitors and use this information to generate a simulated electric bill, identify the loads that are causing the peak demand, and identify the loads that are consuming the most amount of energy on a monthly basis.

Using this detailed load profile information, a facility can better understand what is causing the base energy consumption for a facility and identify areas where to reduce it (i.e. turning off exhaust fans during non-working hours, lowering thermostats to prevent chillers from operating during non-working hours, identifying air leaks in compressed air systems, etc…).

You can also better understand what is contributing to your facility's maximum 15 minute window of energy usage for the month and when a manufacturing process could be rescheduled to dramatically reduce the demand charge.

Understanding a facility's electric load profile also allows you to take advantage of an electric utility's curtailment rates, which lower energy consumption rates in exchange for a negotiated number of load shedding requests per year. A detailed load profile allows a facility to manually or automatically shed non-critical loads during a contracted curtailment.

This detailed load profile information could also be used to provide incentives for department managers to encourage energy conservation and efficiency with their employees. Having department managers be fiscally responsible for their energy costs or financially sharing electric cost savings with employees is a great incentive for reducing overall energy costs in a facility.

They key to managing electrical energy costs is to historically monitor a facility's energy usage in as detail as possible and understand why each line item cost exists on your monthly electronic bill. Because electric motors contribute the most to a manufacturing facility's overall electrical costs, and every electric motor needs an overload relay to comply with government regulations, facilities that have a networked based electronic overload relay already have this electrical energy data. They just need to collect it and analyze it to begin saving on their monthly electric bill.

If you are interested in learning more about the latest in industrial control components and historical data collection systems, visit our web site.


Bill Martin
Bill Martin
Product Manager, Electronic Overload Relays, Rockwell Automation
Bill Martin
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