8.3   Disaggregation of Electrical Circuits

This section of the Standard requires buildings to be wired in a manner that separates loads by types onto independent feeders and risers through the building.  This will require separate feeders and panels for lighting, plug and equipment loads, HVAC loads, etc.  The requirements are contained in Table 130.5-B, reproduced below.

“Disaggregation” means in this case to break down the total electrical use in the building into groups that permit power and energy use measurements to be taken, to enable management to determine where energy is being used.  For instance, lighting energy use quantities and patterns can be studied and excess use or waste can be targeted for improvements.

Note that this requirement does not require any metering.  By placing all load of a particular type on one feeder, a portable power measurement and analysis device can be temporarily attached to its feeder, measurements can be made, and then the device can be moved to another feeder.   

In the examples, note that the manner in which disaggregation occurs does not require specific wiring; for instance, a single feeder can provide lighting and plug load power as long as the panelboard has a split bus allowing measurement of one and then the other.  However, this can only be used in a smaller building as the all lighting must be able to be measured at one point.

This requirement is for new buildings and for major additions or renovations.  It is invoked whenever the service is modified as with a new switchboard, or when sections are added or new feeders pulled.  In an existing building that is being altered, this requirement is not invoked as long as the existing service switchboard, existing feeders and existing panelboards remain essentially “as-is”. 

As an alternative to disaggregation, current transformers can be added to individual branch circuits or loads throughout the building, and a permanent measurement system can be installed.  In this case disaggregated wiring would not be required as long as the metering system permitted the equivalent disaggregated measurements.  See Exception 1 to Section 130.5(b).

8.3.1    Disaggregation increases as loads get larger

The requirement is progressive. Disaggregation is not required until the service reaches 50 kVA, which is 60 amps at 277/480 volts three phase, 150 amps at 120/208 volts, three phase and 200 amps at 120/240 volts single phase.  For most small buildings or separately metered portions of a building, such as a store in a mall, this requirement will not apply.

Once the service to the building reaches 50 kVA, the requirements are applied to some groups regardless of actual load, and to other groups when the group reaches a threshold value of 25 kVA (100 amps at 240 volts single phase, 70 amps at 120/208 volts three phase, and 30 amps at 277/480 volts three phase).

For services rated 250 kVA and above, lighting and plug loads are required to be disaggregated “by floor, type or area”. So in a single-story building, all the lighting loads could be fed from a single panel, and all the plug loads could be fed from another panel (or alternatively, both types of load could be fed from one panel with a split bus). 

In a large single-story building it would be useful, but not mandatory, to split each type of load into sub-panels that serve particular areas or particular types of light fixture, so these could be metered with the same CT. 

In a multi-story building, a simple way to comply would be to install a separate lighting panel and a separate plug-load panel for each floor of the building.  However, it would be equally acceptable and more useful to divide the load according to which area of the building it serves (office, warehouse, corridors etc.), or by the type of light fixture (metal halide vs. fluorescent, dimmable vs. fixed output, etc.).  So, for instance, both the first and second floor office lights could be fed from the same panel, while the warehouse lights would be fed from a second panel.  Dividing the load by area or by type instead of by floor is more likely to yield useful information when the loads are analyzed in an energy audit. Practical Considerations

These requirements were developed with a reasonably practical eye.  In a small building or service, disaggregation is not required at all.  The minimum threshold of 50-kVA service means that almost all projects less than 5,000 sf will not be required to comply.  Slightly larger projects will be able to comply by using carefully laid-out panelboards. The standard envisions the use of conventional panelboards, motor control centers, through wired panels, and other standard wiring methods. It also envisions a new generation of creative solutions such as split bus panels, with separate bus and breaker sections for lighting and receptacles/equipment.  Likewise, clever wiring methods will also emerge, such as connecting all HVAC units to a single feeder from the service, using a combination of through feeds and taps.  In other words, with minor changes in how power is distributed in a building, the requirement can be met with little or no added cost.

In larger buildings, this mandatory requirement will make separate risers for lighting, receptacles/equipment, and HVAC necessary.  Single large loads or groups of loads, such as an elevator machine room, chiller or commercial kitchen, will have a separate feeder and panelboard or motor control center anyway; in many buildings these requirements are already met at least in part.

For buildings with a single large service greater than 50 kVA, such as retail malls, offices and apartment buildings that have submetered distribution to completely demised tenants, the requirements apply as follows:

•      Common areas of the building must be disaggregated

•      Individual submetered services must be disaggregated if the submetered service is 50 kVA or greater, with the exception of residential units, in which disaggregation is not required.

In remodeled or renovated buildings, the total electrical load is expected to be reduced as Title 24 lighting power requirements, HVAC requirements, insulation and glazing requirements, etc. will necessarily cause the original building to use less energy, and to a certain extent a building can be enlarged without increasing the service or existing feeders and panels.  As long as the only changes to the electrical system involve changes to branch breakers and branch circuits, this mandatory requirement is not invoked.

Table 8-1 - Required Disaggregation of Electrical Loads