Demand Load vs. Energy Use: Why kWh Is the Wrong Electrical Test

Can a building's utility consumption or kilowatt-hour data be used to allocate its electrical distribution system in a cost segregation study? The 2025 IRS Cost Segregation Audit Technique Guide draws a clear distinction between energy consumption and the demand-load analysis used for functional allocation. Demand load relates to what the electrical system must be designed and sized to support, while energy usage measures electricity consumed over time. That difference matters because conductors, breakers, transformers, switchgear, capacitors, and conduit are designed around electrical demand, and their required size affects installed cost. For CostSegRx engineers, the principle is straightforward: measuring how much electricity was consumed is not the same engineering analysis as determining what loads drove the design and cost of the electrical distribution system.

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Key Takeaways

• Demand load and energy consumption measure different characteristics of a building's electrical operation.
• Demand load affects how conductors, breakers, transformers, switchgear, capacitors, and conduit are designed and sized.
• The ATG says energy-usage studies measured in kilowatt-hours should not be used for functional allocation.
• Electrical plans, equipment loads, demand factors, panel information, and system design provide the engineering evidence needed for demand analysis.
• Functional allocation connects qualifying demand loads to the cost of the primary and secondary electrical distribution systems.
• Two loads can consume similar annual energy while creating very different electrical design requirements and therefore different allocation implications.
• Energy consumption tells you what was used over time, while demand load helps explain what the electrical system had to be designed to support.

What Is the Difference Between Demand Load and Energy Use?

Demand load and energy use answer different engineering questions.

The ATG describes demand load as an electrical design concept used to determine the overall requirements of the electrical distribution system.

That analysis affects the size of equipment such as conductors, circuit breakers, transformers, switchgear, capacitors, and conduit.

Those components have to be capable of supporting the electrical loads for which the system is designed.

Energy use measures something different.

The ATG discusses energy-usage studies in terms of kilowatt-hours, or kWh.

A kilowatt-hour represents energy consumed over time.

That makes kWh useful for understanding how much electrical energy a property or piece of equipment actually consumed during a particular period.

But that is not the same question as determining the electrical demand that influenced the design of the distribution system.

One measurement describes consumption.

The other helps describe system requirements.

That distinction is fundamental to the ATG's functional allocation methodology.

Why Does Demand Load Affect Electrical System Cost?

Electrical distribution equipment is not sized arbitrarily.

The loads a system must support influence its physical design.

A larger required electrical demand can require larger conductors.

It can require larger circuit breakers.

It can affect transformer capacity.

It can affect switchgear.

It can affect conduit sizing and other portions of the distribution system.

The ATG connects this directly to cost.

Because the size of electrical distribution equipment affects installed cost, the demand associated with different end uses provides a method for allocating the cost of the primary and secondary electrical distribution systems.

That is why the engineering analysis goes beyond simply asking whether electricity eventually reaches § 1245 property.

The engineer needs to understand the load that property places on the electrical system.

The current ATG methodology uses those electrical relationships to proportionally allocate distribution-system costs between § 1245 property and § 1250 property.

CostSegRx engineers therefore need to understand both the end use and the electrical demand associated with it.

Why Does the ATG Reject kWh Energy Studies for Functional Allocation?

Because energy consumption does not measure the same thing as electrical demand.

The ATG specifically distinguishes an energy-usage study from the functional allocation analysis.

It explains that an energy-usage study typically measures electrical energy consumed over a period of time in kilowatt-hours.

These studies are generally performed for purposes such as energy efficiency.

The ATG then makes the key point: an energy-usage study should not be used as part of the functional allocation approach.

Why?

Consider equipment that requires substantial electrical capacity when operating but operates only occasionally.

Its annual kWh consumption could be relatively modest.

Yet the building's electrical distribution system may still have needed to be designed with sufficient capacity to support that equipment when it operates.

Now consider a smaller load that operates continuously.

It could accumulate significant annual energy consumption even though its instantaneous electrical demand and effect on system sizing are much lower.

A kWh comparison could therefore tell a very different story from the design-load analysis.

For functional allocation, the ATG is concerned with the electrical demand used to design and size the distribution system.

That is why utility bills alone do not answer the question.

What Information Supports a Demand-Load Analysis?

Demand-load analysis is an engineering exercise.

The ATG emphasizes the importance of understanding the electrical design of the building and the property served by the electrical distribution system.

Depending on the property and available documentation, CostSegRx engineers may examine electrical one-line diagrams, panel schedules, equipment schedules, design drawings, electrical specifications, connected loads, demand factors, transformer information, switchgear, feeder sizes, conductor sizes, circuit breakers, and actual end uses.

The engineer is trying to reconstruct how the system was designed and what electrical loads it was intended to support.

That can require distinguishing different levels of the electrical system.

Branch circuits do not necessarily use the same demand assumptions as feeders or service equipment.

A branch circuit may need to be designed around the connected equipment it directly serves.

At higher levels of the distribution system, recognized demand factors can account for the fact that not every connected load operates at maximum demand simultaneously.

That distinction matters.

Simply adding every equipment nameplate value together may not reproduce the demand that actually governed the upstream electrical design.

Likewise, reading annual kWh consumption from a utility statement does not establish the design demand.

The engineer has to understand the electrical system itself.

How Does Demand Load Become a Functional Allocation Percentage?

The purpose of the demand analysis is not merely to calculate an electrical statistic.

It supports an allocation of electrical distribution system cost.

Under the ATG methodology, the engineer identifies the property served by the primary and secondary electrical distribution systems and determines the demand associated with the relevant end uses.

Demand associated with qualifying § 1245 property is identified.

Demand associated with § 1250 property and building operation is also identified.

Those demand loads can then be compared to determine a supported proportional allocation.

This methodology is explored more broadly in Electrical Distribution Systems in Cost Segregation Studies.

The critical point is that the percentage should emerge from the property's electrical facts.

It should not come from a historical case percentage.

It should not come from an industry rule of thumb.

And it should not come from the percentage of annual kWh consumed by particular equipment.

Demand load connects the electrical design to the allocation.

Can Similar Energy Consumption Produce Different Electrical Allocations?

Illustrative example only. Actual electrical characteristics, demand factors, classifications, costs, recovery periods, depreciation deductions, and tax results depend on the specific property, engineering analysis, documentation, applicable authority, and taxpayer circumstances.

Assume an industrial property contains two electrical loads.

Equipment A is a large production machine.

When operating, it places a substantial demand on the electrical system, but it runs only during limited production periods.

Equipment B is a smaller building-related load that operates for many more hours throughout the year.

At year-end, assume the two loads have similar measured energy consumption in kWh.

That does not mean they had an equal effect on electrical system design.

Equipment A may have required larger conductors, larger circuit protection, greater transformer capacity, or other distribution capacity to accommodate its operating demand.

Equipment B may consume a similar amount of energy simply because it operates for much longer periods.

An allocation based only on annual kWh could treat the two loads as approximately equal.

A demand-load analysis could show that their impact on electrical design was materially different.

Now assume the supported primary and secondary electrical distribution system cost is $1,000,000.

The functional allocation percentage should come from the supported demand-load methodology described by the ATG, not from dividing annual energy consumption between the two loads.

That distinction can materially change the amount of electrical basis associated with § 1245 property and § 1250 property.

What Is the Most Important Difference Between Demand Load and kWh?

Demand load and energy use should not be treated as interchangeable measurements.

Kilowatt-hours describe energy consumed over time.

Demand load helps describe the electrical capacity the system must support.

That capacity influences the physical design and size of conductors, breakers, transformers, switchgear, conduit, and other electrical distribution components.

Those physical requirements influence cost.

That is why the ATG uses demand-load analysis in its functional allocation methodology and specifically distinguishes that analysis from an energy-usage study.

For CostSegRx engineers, the practical lesson is to trace the engineering logic backward.

What property does the electrical system serve?

What demand does that property place on the system?

How did those loads influence the design and sizing of the distribution infrastructure?

What portion of the supported demand relates to § 1245 property versus § 1250 property?

Only then can the electrical distribution cost be proportionally analyzed under the functional allocation methodology.

Energy consumption tells you how much electricity was used. Demand load tells you what the electrical system had to be designed and sized to support. Functional allocation depends on the second question.