Under Chicago's energy benchmarking ordinance, owners of "covered buildings" (buildings of 50,000 square feet and above in gross floor area that meet certain criteria) are required to report their energy use annually. This reported data is published by the City, so a building's energy performance is visible to prospective tenants, buyers, and the public at large. However, a total of that kind shows how much energy a building used, not which equipment used it.
For building owners who want a more accurate picture of where energy use is occurring, current sensors can provide it. Functional Devices, Inc. manufactures current switches and transducers for building automation, including split-core models suited to Chicago's retrofit-heavy stock.
What an Annual Total Cannot Show
The energy accounted for in a reported total was used by the fans, pumps, chillers, and other motor loads that run inside a building, but the total itself carries no record of that. It shows only that the energy was used, not which equipment used it, when, or whether the use was intended.
A building automation system (BAS) cannot fill that gap on its own, because a BAS knows what it commanded, not what actually happened as a result. Equipment can run outside its schedule. A load can keep drawing after it was commanded off. A motor can lose its belt and keep spinning without moving air. Each of these adds to an annual energy total, and despite looking normal at the controller, each of them is an avoidable expenditure if caught quickly.
Reading Current at the Equipment
A current reading differentiates a load that is running from one that was merely commanded to run. If sensed at enough points, that information can turn a building-level number into a set of equipment-level facts: which loads ran, when, and how hard. The loads found misbehaving can then be fixed, which is the mechanism by which the next reported total is lowered.
However, there are two questions here that must be answered: whether a load is running, and how much energy it is drawing. These questions are answered by two different devices.
Current Switches and Current Transducers
Current switches report whether a load is running. When the monitored current crosses a set threshold, a dry contact closes, and the BAS reads the load as “on.” The RIBXGTA is a split-core adjustable current switch with a 0.75–150 A sensing range and a dry contact output.
Current transducers report how much a load is drawing. The output is an analog signal proportional to the current, so a specific load, a chiller or a large supply fan, can be trended over time and read against the building’s reported total. The RIBXG420 series outputs 4–20 mA for that application.
Sensing Low-Current Loads
Electronically commutated motors (ECMs) and variable-speed pumps draw low, variable current, and the difference between a motor’s standby draw and its running draw can fall below a general-purpose switch’s threshold. The RIBXGTA-ECM senses down to 0.25 A with a tight hysteresis band, so the closed contact reflects a running motor rather than chattering between states while the drive ramps the motor’s speed.
Split-Core Installation for Retrofit Work
Sensing at the equipment level means adding points to circuits that are already in service, and in Chicago’s older stock, those circuits often serve occupied floors. A split-core sensor has a hinged core that opens and clamps around an existing conductor; nothing is cut or re-terminated, and the circuit is not interrupted, so a point can be added without a scheduled shutdown. This same quality makes split-core sensors usable for temporary monitoring during an energy audit: a sensor can be placed, read, and removed without the system being taken offline. These applications are covered in more depth in the guide to current sensors for energy audits and fault detection.
Frequently Asked Questions About Current Sensors
What is the difference between a current switch and a current transducer?
A current switch closes a dry contact when current crosses a set threshold, telling the BAS whether a load is on or off. A current transducer outputs an analog signal proportional to the current, telling the BAS how much the load is drawing. Run status is read with a switch; consumption trending is done with a transducer.
Is a current sensor the same as a current transformer?
No. The current transformer (CT) is the sensing element inside the device. The current sensor is the finished device built around the CT, with the threshold, output contact or analog stage, and housing that make it a field-installable product.
How does a current switch detect a broken belt?
A motor that has lost its load draws less current than one doing work. With the trip threshold set between the two values, the contact opens when the belt breaks, even though the motor keeps running. The BAS sees a stopped status against a run command.
What current sensor works for ECM motors?
The RIBXGTA-ECM is built for low, variable ECM current, sensing down to 0.25 A with tight hysteresis. A standard current switch with a higher minimum threshold can miss the difference between an ECM’s standby and running draw.
Where can I buy current sensors in Chicago?
RIB® current sensors are stocked by authorized Functional Devices distributors in Illinois. A distributor can confirm availability and advise on switch versus transducer selection for the point.
Source Current Sensors in Chicago
Functional Devices manufactures the current switches and transducers used for status and monitoring points in Chicago building automation work. To specify a sensor, browse the current sensor lineup or find an authorized Functional Devices distributor in Illinois.