Electrical Load List — The Starting Point of EPC Electrical Design

Electrical EPC Design Course — Beginner to Professional Level

After understanding the Electrical Design Basis (EDB), the next major step in EPC electrical engineering is understanding the Electrical Load List (ELL).

This is where electrical design starts becoming much more practical.

The Electrical Load List is one of the most important documents in an industrial electrical project because it provides the foundation for several downstream engineering activities, including:

• Transformer sizing
• DG sizing
• MCC/PCC sizing
• Cable sizing
• Single Line Diagram (SLD) development
• Power system studies
• Electrical equipment selection

If you understand the Electrical Load List properly, many of these later topics become much easier.

1. What Is an Electrical Load List?

In simple terms:

An Electrical Load List is a master list of the electrical loads in a plant.

Every electrical load—such as motors, pumps, compressors, fans, lighting systems, and small-power loads—is identified and documented.

For example:

This list gives the electrical engineer the first clear picture of how much electrical capacity the plant requires.

2. Where Does the Load Information Come From?

An important point for a beginner is that the electrical engineer does not normally decide the motor rating independently.

The information comes from other engineering disciplines, equipment vendors, and project documents.

A simplified EPC workflow looks like this:

PROCESS
   │
   ▼
Equipment Requirement
   │
   ▼
MECHANICAL
   │
   ▼
Equipment / Motor Data
   │
   ▼
ELECTRICAL
   │
   ▼
Electrical Load List

For example:

The Process Engineer determines that a cooling-water pump is required.

The Mechanical Engineer develops the pump and motor requirements.

The equipment vendor may then provide detailed motor data.

The Electrical Engineer uses this information to develop the electrical load list and design the electrical supply system.

This is a good example of how different engineering disciplines work together on an EPC project.

3. What Information Is Included in an Electrical Load List?

A real EPC Electrical Load List contains much more information than simply:

Pump = 90 kW

Depending on the company and client requirements, it may contain columns such as:

The exact format and columns will vary from project to project.

Some projects may also include information such as:

• Starting current
• Motor code
• Load category
• Emergency status
• UPS status
• VFD information
• Area classification
• Operating hours
• Load shedding priority
• Source of supply
• Feeder identification

The important thing is to understand why each piece of information is required, rather than trying to memorize every column.

4. Connected Load

The first important concept is Connected Load.

Connected load is the total rated capacity of all loads connected or installed in the electrical system.

Consider the following loads:

Pump 1          90 kW
Pump 2          90 kW
Compressor     500 kW
Fan 1           55 kW
Fan 2           55 kW
Lighting        50 kW
Small Power     30 kW

The total connected load is:$$90 + 90 + 500 + 55 + 55 + 50 + 30$$$$= 870\ kW$$

Therefore:

Connected Load = 870 kW

This represents the total installed/rated load in this simplified example.

5. Is the Entire Connected Load Always Consumed?

No.

This is one of the most important concepts to understand.

Consider two pumps:

P-101 → DUTY
P-102 → STANDBY

Both pumps may be installed in the plant.

Therefore, both contribute to the installed or connected capacity.

However, under normal operating conditions:

P-101 → Running
P-102 → Standby

Only one pump is normally operating.

Therefore:

Installed capacity does not necessarily equal operating demand.

This is why EPC engineers need to consider operating philosophy and factors such as:

• Demand factor
• Diversity
• Load factor
• Duty/standby arrangement
• Operating conditions

6. Running Load

The running load represents the electrical load expected to be operating under a particular operating condition.

Let’s use the previous example.

For normal operation, the running loads are:

• P-101 = 90 kW
• C-101 = 500 kW
• F-101 = 55 kW
• Lighting = 50 kW
• Small Power = 30 kW

Therefore:$$90 + 500 + 55 + 50 + 30$$$$= 725\ kW$$

So:

Installed/Connected Load = 870 kW

Normal Running Load = 725 kW

This distinction is fundamental to electrical load calculations.

7. Demand Load

The next concept is Demand Load.

The maximum electrical load that the plant is expected to require during a particular operating condition may be lower than the total connected load.

For example:

Connected Load = 870 kW
Maximum Demand = 700 kW

Therefore:

Connected load = 870 kW

Maximum demand = 700 kW

The actual demand calculation depends on the plant operating philosophy and the assumptions defined by the project.

8. Demand Factor

A commonly used relationship is:$$Demand\ Factor = \frac{Maximum\ Demand}{Connected\ Load}$$

Suppose:

• Connected Load = 870 kW
• Maximum Demand = 700 kW

Then:$$DF = \frac{700}{870}$$$$DF \approx 0.805$$

Therefore:

Demand Factor ≈ 0.81

A demand factor below 1 indicates that the maximum demand is less than the total connected load.

9. Diversity Factor

Diversity Factor is another important concept in electrical system design.

It is based on the fact that different loads do not necessarily reach their individual maximum demands at exactly the same time.

For example:

Pump system      → High demand
Lighting         → Moderate demand
HVAC             → High demand
Workshop         → Low demand

Each system may have its own maximum demand.

However, the maximum demand of the entire plant may not occur when every individual load is simultaneously operating at its own maximum.

Therefore:

The total plant demand can be lower than the simple sum of all individual maximum demands.

This concept becomes particularly important when designing large electrical distribution systems.

10. Duty and Standby Loads

Duty/standby arrangements are extremely common in EPC projects.

Consider:

P-101 → 90 kW → DUTY
P-102 → 90 kW → STANDBY

The installed capacity is:$$90 + 90 = 180\ kW$$

However, if only P-101 operates during normal conditions:$$Normal\ Running\ Load = 90\ kW$$

Therefore:

Installed Capacity = 180 kW

Normal Operating Load = 90 kW

This is why you should always check the status and operating philosophy of each load before using it in an electrical calculation.

11. Building a Simple EPC Electrical Load List

Let’s build a small practical load list.

Step 1 — Calculate Installed Load

Add all equipment ratings:$$90 + 90 + 500 + 55 + 55 + 50 + 30$$$$= 870\ kW$$

Therefore:

Installed Load = 870 kW

Step 2 — Calculate Normal Running Load

Include the loads operating under the assumed normal operating condition:$$90 + 500 + 55 + 50 + 30$$$$= 725\ kW$$

Therefore:

Normal Running Load = 725 kW

This simple calculation demonstrates why a load list is more than just a list of equipment.

It also captures how the plant is expected to operate.

12. Why Is the Electrical Load List So Important?

The Electrical Load List becomes an input to many other engineering activities.

A simplified engineering flow is:

                ELECTRICAL LOAD LIST
                         │
          ┌──────────────┼──────────────┐
          ▼              ▼              ▼
    Transformer          DG          MCC/PCC
       Sizing           Sizing         Sizing
          │              │              │
          └──────────────┼──────────────┘
                         ▼
                       SLD
                         │
                         ▼
               Power System Studies
                         │
                         ▼
             Cable & Protection Design

For example, when someone asks:

“Why was this transformer selected?”

A professional electrical engineer should eventually be able to trace the answer back through the design calculations to the Electrical Load List, Electrical Design Basis, and project operating philosophy.

This traceability is very important in EPC engineering.

13. kW vs kVA — A Very Important Concept

One of the most important concepts for an electrical design engineer is understanding the difference between kW and kVA.

kW — Active Power

kW represents the real or active power consumed by the load.

kVA — Apparent Power

kVA represents apparent power.

For a given power factor:$$kVA = \frac{kW}{PF}$$

Suppose the running load is:

725 kW

and the power factor is:

0.85

Then:$$kVA = \frac{725}{0.85}$$$$\approx 853\ kVA$$

Therefore:

725 kW at 0.85 power factor corresponds to approximately 853 kVA.

This is important because transformers and many other electrical equipment are commonly rated in kVA or MVA, rather than kW.

However, the final transformer selection cannot be made from this number alone.

Other considerations may include:

• Future margin
• Transformer loading
• Redundancy
• Ambient conditions
• Motor starting requirements
• Voltage level
• Standard transformer ratings
• Project specifications
• Operating philosophy

This is the engineering thought process we will build throughout the course.

14. The Five Concepts You Must Understand

At this stage, don’t try to memorize dozens of formulas.

Focus on these five concepts.

① Connected Load

The total installed/rated load.

② Running Load

The load expected to operate under a particular operating condition.

③ Demand Load

The expected maximum demand under the defined operating conditions.

④ Duty/Standby

Installed equipment does not necessarily mean simultaneous operation.

⑤ kW and kVA

For a given power factor:$$kVA = \frac{kW}{PF}$$

Understanding these five concepts will make the upcoming electrical design calculations much easier.

🧠 A Simple Way to Think Like an EPC Engineer

Whenever you see an electrical load, don’t immediately ask:

“How many kW is it?”

Start asking:

1. What equipment is this?
2. Is it duty or standby?
3. Does it run continuously?
4. What is its operating load?
5. What is its power factor?
6. What voltage does it use?
7. Is it normal, emergency, or UPS load?
8. What happens when the equipment fails?
9. Does it operate simultaneously with other loads?
10. What electrical system will supply it?

This way of thinking is much more valuable than simply memorizing formulas.

🎯 Lesson 4 — Exercise

Consider the following plant loads:

Calculate the following:

1. Total Connected Load

Add the rating of all installed equipment.

2. Normal Running Load

Include the equipment that is expected to operate normally.

Remember:

• Pump A → Running
• Pump B → Standby
• Compressor → Running
• Fan A → Running
• Fan B → Standby
• Lighting → Running
• Small Power → Running

3. Running Load in kVA

Assume:

Power Factor = 0.8

Use:$$kVA = \frac{kW}{PF}$$

Take your time with the calculation.

Making mistakes at this stage is completely normal. The important thing is to understand why you are including or excluding each load.

🚀 What Comes Next?

Now we know what loads exist in the plant and how to calculate the basic electrical demand.

The next question is:

How do we decide which voltage levels should be used to distribute this power around the plant?

That takes us to:

Lesson 5 — Electrical Power Distribution System

In the next lesson, we will learn:

• How plant voltage levels are selected
• HV, MV and LV systems
• How transformers fit into the distribution system
• How electrical power flows through an industrial plant
• PCC and MCC
• Main and sub-distribution systems
• How to develop a basic Single Line Diagram (SLD)
• Why large motors may use MV
• How an EPC engineer starts building the plant electrical network

This is where we start connecting the Load List → Transformer → Switchgear → MCC/PCC → Cables → Loads into one complete electrical system. ⚡