Due to increasingly high electric utility rates here in Arizona, I purchased a thermostat and controller for each of my two AC units so they can be operated remotely. We have units on the first and second floors with thermostats that monitor our location in the house. If we are gone, they adjust the temperature accordingly.

Depending on how and when your electric utility charges peak rates, such smart thermostats can also adjust the operation time of your AC units. In our area, the utility charges extra for the peak hours of 4 p.m. to 7 p.m. on weekdays, with no peak times on weekends and holidays. We run only one unit during these hours, thus decreasing the peak operation of our electrical equipment.

The future is now

The hub that ties these thermostats together can also control smart lighting, the TV and other devices. It can stream your favorite music and be an alarm clock (plus, you can turn it off for sleep mode at the sound of your voice). It can lock and unlock doors and open or close your garage door, as well as alert you when you forget to close it.

Electrically controlling our homes and lives is not just a dream for the future. It has begun with these kinds of smart controls designed into a home’s electrical system. 

Obviously, it is easier to design and install electronic control and energy management systems for new homes than to retrofit existing ones. However, many energy management and burglar alarm systems are based on 24V Class 2 power-limited systems covered in Article 725 of the NEC. Since the cabling can be easily concealed, these lower energy systems can be a good option for retrofits.

Energy management systems for commercial applications and large homes may require higher control voltages with monitoring of current and function by using current transformers located at the branch circuit overcurrent protective device. Whether using power-limited or nonpower-limited installations, it is necessary to appropriately mark controlled equipment.

Code specifications

Article 750 applies to the installation and operation of energy management systems, but seems to apply more to large commercial installations than to smaller residential systems. Regardless, we can still take direction from some of the requirements in Article 750. For example, 750.30 states that an energy management system must not cause a branch circuit, feeder or service to be overloaded. That is widely applicable common sense.

More specifically, Section 750.30(C)(4) requires the equipment that supplies the branch circuit, feeder or service to be field marked with the following information: maximum current setting, date of calculation and setting, identification of loads and sources associated with the current-limiting feature and the following or equivalent wording: “The setting for the EMS current limiting feature shall not be bypassed.”

The markings at the equipment supplied by the branch circuit must meet the requirements in 110.21(B) and be located so they are clearly visible to qualified persons before equipment examination, adjustment, servicing or maintenance. 

Remember in the 2023 NEC, 110.22(A) now requires compliance with the following: “Each disconnecting means must be legibly marked to indicate its purpose unless located and arranged so the purpose is evident. In other than one- or two-family dwellings [although this is still a good idea for those locations], the marking shall include the identification and location of the circuit source that supplies the disconnecting means, unless located and arranged so the identification and location of the circuit source is evident. The marking shall be of sufficient durability to withstand the environment involved.”

Section 750.50 requires a directory, as follows: “Where an energy management system is employed to control electrical power through the use of a remote means, a directory identifying the controlled device(s) and circuit(s) must be posted on the enclosure of the controller, disconnect, or branch-circuit overcurrent device.”

Compliance with these rules ensures that service personnel know there is an energy management system for troubleshooting and control and adjustment of loads. 

These requirements are a matter of safety for service personnel working on and maintaining dwelling unit equipment.

stock.adobe.com / Afly / Julia