How an EPC Electrical Engineer Actually Works: A Practical Guide for Beginners

Introduction

In the previous lesson, we learned what EPC means. Now we move to the next important question:

What does an electrical engineer actually do inside an EPC project?

The purpose of this lesson is to understand the overall workflow of an EPC electrical engineer before we start detailed electrical calculations.

If you are a beginner, don’t worry if some of the terms look unfamiliar. We will study each topic in detail in the upcoming lessons.

1. Imagine a Real EPC Project 🏭

Let’s use one project throughout our learning journey:

New Process Plant — 100 MW Electrical Load

The client wants a complete industrial plant to be designed, constructed, tested, and commissioned.

An EPC project normally involves several engineering disciplines working together.

                         CLIENT
                            │
                            ▼
                     EPC CONTRACTOR
                            │
          ┌─────────────────┼─────────────────┐
          ▼                 ▼                 ▼
       PROCESS           MECHANICAL       ELECTRICAL
          │                 │                 │
          ├─────────────────┼─────────────────┤
          │                 │                 │
          ▼                 ▼                 ▼
   INSTRUMENTATION         CIVIL             HVAC

An important point

Electrical engineering cannot work independently.

A large part of EPC engineering involves:

• Receiving information from other disciplines
• Developing electrical engineering based on that information
• Providing electrical information back to other disciplines
• Coordinating with procurement and construction
• Supporting testing and commissioning

This coordination is one of the most important parts of working as an EPC electrical engineer.

2. Where Does Electrical Engineering Get Its Information?

This is one of the most important concepts for a beginner to understand.

Suppose the process engineer says:

“We need a pump to move liquid from Tank A to Tank B.”

The process engineer determines the process requirement.

The mechanical engineer may then select and specify the pump.

The electrical engineer does not decide the process flow.

Instead, electrical receives information required to design the power supply.

Typical information may include:

• Motor rating
• Motor voltage
• Motor efficiency
• Power factor
• Starting method
• Motor speed
• Number of motors
• Duty/standby arrangement
• Hazardous-area classification

Electrical then designs the electrical power supply for the motor.

Example

Mechanical tells electrical:

Pump P-101 → Motor 250 kW, 6.6 kV

Now electrical has to answer:

How do I supply this motor safely and reliably?

A simplified arrangement could look like this:

        6.6 kV SWITCHGEAR
                │
                │
              Cable
                │
                ▼
          250 kW MOTOR
                │
                ▼
            PUMP P-101

Electrical must then determine several things, such as:

• Cable size
• Breaker size
• Protection
• CT ratio
• Relay settings
• Starting method
• Voltage drop
• Short-circuit withstand
• Earthing
• Cable routing

This is the basic mindset of electrical design:

Other disciplines define their equipment requirements, and electrical develops the system required to supply and protect that equipment.

3. Electrical Design Starts With Inputs 📋

One common mistake beginners make is thinking:

“I received a project, so I should start drawing the SLD.”

Not yet.

Before starting detailed design, you need to understand the design inputs.

Electrical engineering normally receives information from several sources.

Client Documents

Typical client inputs include:

• Project specifications
• Electrical specifications
• Design criteria
• Applicable standards
• Utility requirements
• Reliability requirements

Process Inputs

Typical process information includes:

• Process description
• Process Flow Diagrams (PFDs)
• Equipment list
• Motor list
• Critical equipment

Mechanical Inputs

Mechanical may provide information related to:

• Motors
• Package equipment
• Pumps
• Compressors
• Fans
• HVAC equipment

Instrumentation Inputs

Instrumentation may provide:

• Control philosophy
• Instrument power requirements
• Emergency shutdown requirements
• UPS loads

Civil Inputs

Civil information may include:

• Electrical room dimensions
• Substation locations
• Cable trench requirements
• Equipment foundations

Why are these inputs important?

Because electrical design decisions depend on information from the complete plant.

You cannot properly design the electrical system if you don’t understand what equipment the plant contains and what that equipment requires.

4. What Does Electrical Engineering Produce?

Now the process works in the opposite direction.

Electrical takes the information received from the client and other disciplines and converts it into engineering documents, calculations, drawings, and specifications.

A simplified EPC electrical workflow looks like this:

CLIENT REQUIREMENTS
        ↓
ELECTRICAL DESIGN BASIS
        ↓
LOAD LIST
        ↓
LOAD CALCULATIONS
        ↓
POWER SYSTEM PHILOSOPHY
        ↓
SINGLE LINE DIAGRAM
        ↓
EQUIPMENT SIZING
        ↓
SHORT CIRCUIT STUDY
        ↓
LOAD FLOW STUDY
        ↓
VOLTAGE DROP STUDY
        ↓
CABLE SIZING
        ↓
PROTECTION
        ↓
EARTHING
        ↓
LIGHTING
        ↓
LAYOUTS
        ↓
MTO
        ↓
PROCUREMENT
        ↓
CONSTRUCTION
        ↓
COMMISSIONING

Notice something important:

These documents are connected.

They are not independent drawings or calculations.

One engineering decision becomes an input for another engineering activity.

Understanding these dependencies is extremely important for becoming a professional EPC electrical engineer.

5. Understanding the Engineering Dependency 🔗

Let’s take a simple example.

Suppose our plant has 10 motors.

Before selecting major electrical equipment, we need to understand the electrical loads.

For example:

Motor List

M-001 → 90 kW
M-002 → 110 kW
M-003 → 250 kW
M-004 → 55 kW
...

↓

Load List

The motor information is collected into the electrical load list.

We then determine:

• Connected load
• Demand load
• Operating load
• Standby loads
• Essential loads
• Emergency loads

↓

Transformer Sizing

Based on the electrical load and design criteria, we may determine a transformer requirement.

For example:

Required transformer = 2500 kVA

↓

Switchgear

Now we can determine the approximate incoming current and consider the required switchgear ratings and fault withstand capability.

↓

Cable Sizing

Once the electrical arrangement is known, we can determine the cables required between the transformer and switchboards or loads.

↓

Protection

Finally, we develop appropriate breaker and relay requirements based on the system and study results.

The important lesson is:

Electrical engineering is a chain of dependent decisions.

A change in one part of the design can affect many other documents.

6. The Biggest Job of an EPC Electrical Engineer ⚡

A common misconception is:

“An electrical engineer’s job is mainly calculating cable sizes.”

❌ No.

Cable sizing is only one part of electrical engineering.

A professional EPC electrical engineer needs to understand the complete electrical system.

For example, imagine this system:

132 kV
   ↓
TRANSFORMER
   ↓
11 kV SWITCHGEAR
   ↓
11 kV MOTOR

You should eventually be able to ask:

• Why is the incoming voltage 132 kV?
• Why is the distribution voltage 11 kV?
• Why was this transformer rating selected?
• What is the fault level?
• What breaker rating is required?
• What protection is required?
• How is the motor started?
• What happens if the motor trips?
• How is the neutral grounded?
• What cable is required?
• How is the cable routed?
• How is the equipment earthed?

This is the system-level thinking we are going to develop throughout this learning series.

7. What Happens During Detailed Engineering?

Let’s imagine that a new EPC project has just started.

Step 1 — Receive Project Documents

Electrical receives information such as:

• Client specifications
• Process information
• Equipment list
• Preliminary motor list
• Site information

↓

Step 2 — Prepare the Electrical Design Basis

Electrical establishes the fundamental design rules for the project.

For example:

Main distribution voltage = 11 kV

LV voltage = 415 V

Frequency = 50 Hz

System grounding = specified philosophy

Lighting voltage = 230 V

Emergency power philosophy = DG/UPS

These decisions are extremely important because they affect the design activities that follow.

8. Then Comes the Load List ⚡

The electrical load list is one of the most important documents in an EPC electrical project.

A simplified example could look like this:

Suppose the total connected load becomes:

5,000 kW

Does that mean we automatically select a transformer exactly equal to 5,000 kW?

Not necessarily.

Why?

Because not every load operates at maximum load at the same time.

This introduces concepts such as:

• Demand factor
• Diversity factor
• Load factor
• Operating factor

We will study these concepts carefully in later lessons.

9. Developing the Single Line Diagram

Once we understand the electrical loads and the overall power system philosophy, we can develop the Single Line Diagram (SLD).

A simplified example is:

                    UTILITY
                       │
                     132 kV
                       │
                       ▼
              ┌─────────────────┐
              │   132/11 kV     │
              │   TRANSFORMER   │
              └─────────────────┘
                       │
                     11 kV
                       │
                       ▼
              ┌─────────────────┐
              │  11 kV          │
              │  SWITCHGEAR     │
              └─────────────────┘
                  │          │
                  │          │
                11 kV      11 kV
                  │          │
               Motor     Transformer
              500 kW       11/0.415 kV
                             │
                            415 V
                             │
                             ▼
                     LV SWITCHBOARD
                             │
                   ┌─────────┼─────────┐
                   │         │         │
                  MCC       LDB        DB
                   │
                 Motors

At first glance, an SLD may look complicated.

Don’t worry.

We will eventually learn how to develop an SLD from the very beginning, including why each component is required.

10. Procurement 📦

Once the electrical design is sufficiently developed, equipment needs to be purchased.

Electrical engineers may prepare technical requisitions for major equipment.

Example:

11 kV Switchgear Technical Requisition

The technical requisition may specify requirements such as:

• Voltage
• Current
• Short-circuit rating
• Busbar rating
• Breaker type
• Protection
• CTs
• VTs
• Metering
• Enclosure
• Applicable standards
• Environmental conditions

Vendors then submit their technical offers.

Electrical engineers review these offers and perform a:

Technical Bid Evaluation (TBE)

A simplified comparison could look like this:

The electrical engineer evaluates the technical compliance and recommends the technically acceptable vendor.

11. Construction 🏗️

After procurement, the equipment reaches the construction site.

Electrical engineering and construction teams may be involved in activities such as:

• Equipment installation
• Cable tray installation
• Cable pulling
• Cable termination
• Earthing
• Junction boxes
• Lighting installation
• Testing
• Inspection

Construction teams may also raise technical issues.

For example:

TQ — Technical Query

“The specified cable tray route clashes with a mechanical pipe. Can the route be changed?”

Electrical engineering reviews the issue and coordinates with mechanical, civil, construction, and other relevant disciplines to resolve it.

This is another example of why EPC engineering is highly interdisciplinary.

12. Commissioning ⚙️

Finally, the project moves toward testing and commissioning.

The overall sequence is:

DESIGN
   ↓
PROCUREMENT
   ↓
INSTALLATION
   ↓
TESTING
   ↓
ENERGIZATION
   ↓
COMMISSIONING
   ↓
OPERATING PLANT

Electrical testing may include:

• Insulation resistance testing
• Continuity testing
• Earth resistance testing
• Transformer testing
• CT/PT testing
• Circuit breaker testing
• Relay testing
• Functional testing
• Interlock testing
• Energization

The objective is to make sure that the installed electrical system operates safely and according to the design requirements.

🧠 The EPC Electrical Engineer’s Big Picture

If you remember only one thing from this lesson, remember this:

Inputs → Engineering → Procurement → Construction → Testing → Operating Plant

Electrical engineering sits in the middle of this entire process.

The electrical engineer does not simply perform calculations.

The engineer must understand:

Where the information comes from → how it is converted into design → how equipment is selected → how the system is constructed → how it is tested → how the plant operates.

That is the mindset we are going to develop throughout this series.

🎯 Your First Practical Exercise

Now let’s test your understanding.

Imagine you receive the following plant equipment information:

Question 1

What is the total connected load?

Question 2

If the plant operates at different loads and only some equipment runs simultaneously, would you design the transformer exactly equal to the connected load?

Question 3

Which discipline would normally provide the motor rating?

Question 4

After receiving the load information, what major electrical document would you develop to show how the loads are supplied?

🚀 What’s Next?

Try answering these four questions yourself.

Don’t worry about getting them wrong.

The purpose of these exercises is to develop your engineering thinking step by step.

In the next lesson, we will start with one of the most important EPC electrical documents:

⚡ Lesson 3 — Electrical Design Basis

We will learn:

• What an Electrical Design Basis is
• Why it is required
• What information it contains
• How voltage levels are selected
• Frequency
• System grounding
• Reliability philosophy
• Emergency power
• Design standards
• Typical EPC project requirements

And most importantly, we will connect the Design Basis → Load List → SLD → Equipment Sizing step by step.

This is where the real electrical EPC design journey begins. ⚡