# how to do load calculation for office or apartments

As an electrical design engineer they should know why load calculation is very important for before doing any electrical works. in general the electrical load calculation is done before they sizing electrical supply for domestic and industrial purpose. here we will see about why we should we need load calculation and how to calculate the load calculation .

## Why should we need load calculation:

There are three important factors behind the load calculation,

1.Sizing of incomer source

- a) Ministry supply b) Generator
- Prepare the load distribution
- Selection of protection device

we will see one by one briefly below,

**Sizing of incomer source**

Generally any industry or domestic construction required electrical power for their equipment’s or appliances. so that purpose they have to calculate electrical load first, then only they can sizing the incomer supply. there are two option available in any country for incomer supply.

- government supply
- self power producing by generator

**For example: **

we need power supply for our office and we are choosing with generator supply. Now we need to find generator sizing?

In this case we have to prepare load calculation first,

**Load calculation **:

for making load calculation we should need load details that is what are the load we are going to use or connect to our power supply.let us consider below load details for our office and we will do load calculation.

S.No |
Electrical appliances |
Watts |
quantity |
Total watts |

1. | Air Conditioner, 2 TON, Single Phase |
2400 | 5 | 12000 |

2. |
Tube Lights |
72 | 20 | 1440 |

3. | Personal Computer(PC) |
1600 | 15 | 24000 |

4. | Printer |
500 | 3 | 1500 |

5. | Geezer |
1500 | 3 | 4500 |

6. | Microwave Oven |
1400 | 1 | 1400 |

7. | Elect. Kettle |
2400 | 1 | 2400 |

as per the load details we can calculate total loads required,

so our total load is = 47240 watts

load = 47.24KW

**Generator Sizing:**

Based on our total load we can easily sizing the generator,

according to IEC standard, the generator capacity should be 125% of total load .

(Note: its include 25% for future purpose)

so our total load is 47.24KW and 125% of total load is 60KW.

so we need 60KW or 75KVA generator for our connecting load.

**Load distribution**

You have to distribute your load in balanced way otherwise its leads to voltage drop and reduce the efficiency of generator. so prevent this problem we should calculate load calculation

For example:

We have 60 kw total load and we have 3 phase 415v 50Hz power supply. Then how to we distribute the load

**TOTAL LOAD = 60KW**

Connecting load |
R PHASE |
Y PHASE |
B PHASE |

LOAD 1(10KW) |
10 |
||

LOAD 2 (10KW) |
10 |
||

LOAD 3 (10KW) |
10 |
||

LOAD 4 (10KW) |
10 |
||

LOAD 5 (10KW) |
10 |
||

LOAD 6 (10KW) |
10 |

**Selection of protective device for incomer**

If you know the total load and load distribution then you can easily select the protective device

There are 5 main protective device for incomer.

1.ELCB

2.RCCB

3.MCCB

4.Isolator

5.MCB

Based on load we can select our main incomer ELCB and MCCB

For example: total load is 60KW then ELCB rating should be

4pole 200Amp.