# How To Prepare Schedule of Loads

Schedule of load preparation is essential and a basic calculation for electrical engineers. In this process the proper sizing of conductors, overload protection and conduits are determined.

While there are different methods doing an electrical design but there is only one thing that cannot be altered --- code requirements must be followed.

- This example emphasized the procedure rather than mimicking the actual loads of a residential unit.
- In this example the voltage drop and short circuit calculation is not included.
- The system voltage of this example is 220 VAC, 60 Hz.

**Schedule of Loads**
Ckt |
Load |
Ph |
Rating Per outlet |
No. of Outlets |
VA |
Volts |
Amps |
Wire |
CB |
Cond. |

1 |
L.O. |
1 |
100 VA |
12 |
1,200 |
220 |
5.45 |
#14 TW |
15 AT, 1P |
½” dia. |

2 |
L.O. |
1 |
100 VA |
9 |
900 |
220 |
4.09 |
#14 TW |
15 AT, 1P |
½” dia. |

3 |
L.O. |
1 |
100 VA |
6 |
600 |
220 |
2.73 |
#14 TW |
15 AT, 1P |
½” dia. |

4 |
C.O |
1 |
180 VA |
10 |
1,800 |
220 |
8.18 |
#12 TW |
20 AT, 1P |
¾” dia. |

5 |
C.O |
1 |
180 VA |
12 |
2,160 |
220 |
9.82 |
#12 TW |
30 AT, 1P |
¾” dia. |

6 |
ACU |
1 |
2.5 HP |
1 |
2331 |
220 |
10.60 |
#10 TW |
30 AT, 1P |
¾” dia. |

7 |
ACU |
1 |
2.5 HP |
1 |
2331 |
220 |
10.60 |
#10 TW |
30 AT, 1P |
¾” dia. |

8 |
ACU |
1 |
2.5 HP |
1 |
2331 |
220 |
10.60 |
#10 TW |
30 AT, 1P |
¾” dia. |

9 |
Range Load |
1 |
5000 W |
1 |
5000 |
220 |
22.71 |
# 8 TW |
80 AT, 1P |
1.0” dia. |

Schedule of loads are just a summary of data to easily identify and facilitate the necessary values and equipment rating to be used in any electrical installation. Any data given in the schedule of loads were backed by calculation based on a well settled electrical principles and code requirements.

I = 1,200 VA/ 220 V = 5.45 Ampere

I = 900 VA/ 220 V = 4.09 Ampere

I = 600 VA/ 220 V = 2.72 Ampere

I = 1,800 VA/ 220 V = 8.18 Ampere

Continuous loads = 9,963 VA or 45.29 A @ 220V (lighting loads and ACU)

Total Loads = 19, 923 VA

Main Feeder Current = (45.29 x 100% ) + (40.72 x 125%) = 96.19 Amperes [4]

Use 50 sqmm TW cable as main feeder or service entrance wire

Use 100 Ampere MCCB, 1 pole - 10 kAIC*

1. NEC 210-9a - Maximum to be served by branch circuit must not be less than 80% of the ampacity of the condutor

2. NEC 430 -22 = The size of the wire supplying motorized load shall not be less than 125% of the rated full load current of the motor.

3. NEC 430- 52 = The size of the branch circuit protection for motor loads shall not be greater than 250% of motor full load current for CB and 300% for non-time delay fuses on full voltage starting.

4. NEC 210-22(C) = Over-Current Protection Device shall be calculated as 100% of non-continuous load + 125% of the continuous load.

1. National Electrical Code 2011 (Handbook)

2. General Electric Circuit Breaker Catalogue

**The general rule: The cable and circuit breaker must always be coordinated.**

**Computations**__Circuit 1:__

I = 1,200 VA/ 220 V = 5.45 Ampere

**Wire**= 5.45 / 80% = 6.82 Amperes ,

__Use 2.0 sqmm TW wire or #14 AWG__[1]

**Circuit Breaker**=

__Use 15 A Circuit Breaker__

**Conduit**=

__Use 1/2" diameter PVC conduit.__

__Circuit 2:__

I = 900 VA/ 220 V = 4.09 Ampere

**Wire**= 4.09/ 80%= 5.11 Amperes ,

__Use 2.0 sqmm TW wire or #14 AWG__

**Circuit Breaker**=

__Use 15 A Circuit Breaker__

**Conduit**=

__Use 1/2" diameter PVC conduit.__

Circuit 3:

Circuit 3:

I = 600 VA/ 220 V = 2.72 Ampere

**Wire**= 2.72/ 80%= 3.41 Amperes ,

__Use 2.0 sqmm TW wire or #14 AWG__

**Circuit Breaker**= 6.82 Amperes,

__Use 15 A Circuit Breaker__

**Conduit**=

__Use 1/2" diameter PVC conduit.__

__Circuit 4:__

I = 1,800 VA/ 220 V = 8.18 Ampere

**Wire**= 8.18/ 80%= 10.23 Amperes ,

__Use 3.5 sqmm TW wire or #12 AWG__

**Circuit Breaker**=

__Use 20 A CB__

**Conduit**=

__Use 3/4" diameter PVC conduit.__

Read: What are the Different Electric Current Symbols According to IEC Standard

I = 2,160 VA/ 220 V = 9.82 Ampere

VA = [ 2.5 HP x ( 746 Watts/ HP ) ] / 0.8 pf (assume 0.8 pf)

VA = 2331 VA

I = 2,331 VA/ 220 V = 10.60 Ampere

VA = 5000 W / 1.0 pf (heating load is a resistive load w/ 100% pf)

VA = 5,000 VA

I = 5, 000 VA/ 220 V = 22.72 Ampere

Circuit 5:Circuit 5:

I = 2,160 VA/ 220 V = 9.82 Ampere

**Wire**= 9.82/ 80% = 12.27 Amperes ,__Use 3.5 sqmm TW wire or #12 AWG__**Circuit Breaker**=__Use 20 A CB__**Conduit**=__Use 3/4" diameter PVC conduit.____Circuit 6-8:__VA = [ 2.5 HP x ( 746 Watts/ HP ) ] / 0.8 pf (assume 0.8 pf)

VA = 2331 VA

I = 2,331 VA/ 220 V = 10.60 Ampere

**Wire**= 10.60 x 125% = 13.24 Amperes ,__Use 3.5 sqmm TW wire or #12 AWG [2]__**Circuit Breaker**= 5.45 x 250% = 26.5 Amperes,__Use 30 A Circuit Breaker [3]__**Conduit**=__Use 3/4" diameter PVC conduit.__

**Note: since the breaker is 30 Ampere, we need to increase the cable size to 5.5 sqmm (rated 30 amps by NEC ) to maintain the coordination of cable and the circuit breaker**.

__Circuit 9:__VA = 5000 W / 1.0 pf (heating load is a resistive load w/ 100% pf)

VA = 5,000 VA

I = 5, 000 VA/ 220 V = 22.72 Ampere

**Wire**= 22.71 / 80% = 28.41 Amperes ,__Use 8.0 sqmm TW wire or #8 AWG__**Circuit Breaker**=__Use 40 A Circuit Breaker__**Conduit**=__Use 1.0" diameter PVC conduit.__

#### Read: How to Select Proper Type of Miniature Circuit Breakers MCBs

**Main Feeder**

**By inspection:**

Continuous loads = 9,963 VA or 45.29 A @ 220V (lighting loads and ACU)

__Non- Continuous = 8, 960 VA or 40.72 @ 220V (conv. outlet & range load)__

Total Loads = 19, 923 VA

Main Feeder Current = (45.29 x 100% ) + (40.72 x 125%) = 96.19 Amperes [4]

Use 50 sqmm TW cable as main feeder or service entrance wire

Use 100 Ampere MCCB, 1 pole - 10 kAIC*

*note: 10 kAIC is just an assumed value, we need short circuit calculation to determine the right specs of the OCPD to be used in this example*

__Rules Applied:__1. NEC 210-9a - Maximum to be served by branch circuit must not be less than 80% of the ampacity of the condutor

2. NEC 430 -22 = The size of the wire supplying motorized load shall not be less than 125% of the rated full load current of the motor.

3. NEC 430- 52 = The size of the branch circuit protection for motor loads shall not be greater than 250% of motor full load current for CB and 300% for non-time delay fuses on full voltage starting.

4. NEC 210-22(C) = Over-Current Protection Device shall be calculated as 100% of non-continuous load + 125% of the continuous load.

**References:**1. National Electrical Code 2011 (Handbook)

2. General Electric Circuit Breaker Catalogue

Thank you

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ReplyDeletequestion 1: circuit 4; how did you compute circuit breaker: 20.45 amps?

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