Cable Amepre Capacity For Motor

Simple tips for select cable size for a motor:

 When you want to select a cable for motor, you need to calculate 125% to 150% load current of motor rating current. It is necessary for the high starting ampere of motor. If you select cable as rating of motor, it should be burn within some time. So, for safety, you should select a cable over the ampere rating of the motor.  

For example, for a 3 phase 30 Kw motor has running on 400 V with Power factor 0.8 and efficiency is 80%

Here, P = 30 kw = 30 × 1000 = 30000 W

V = 400 v

Power factor, Cos θ = 0.8

Efficiency, η = 80% = 0.8

From the power law,

P = √3ηVICos θ

30000 = 1.73 × 0.8 × 400 × I × 0.8                [√3 = 1.73…]

I = 30000 / 442.88

I = 67.74

So, you need to select,

67.74 × 1.25 = 84. 675 Ampere Capacity Cable

                              Or,

67.74 × 1.5 = 101.61 Ampere Capacity Cable

Now, you can easily select cable for your motor.

DOL (Direct On-Line) Starter

Circuit Diagram of DOL (Direct On-Line) Motor Starter:

Star - Delta Motor Circuit

Motor Controlling Circuit: Star - Delta

Types of Conductor

Types of Conductor

Washer - Types and usage

Frequently Using Washers:

Washer Picture	Washer Name	Details
	Flat	Used to distribute Load. Available in SAE, USS and other patterns.
	Fender	An oversize flat washer used to further distribute load especially on soft material.
	Finishing	A washer used to obtain a finish look. Usually used with over head screw.
	Split Lock	The most common style of washer used to prevent nuts and bolts from backing out.
	External Tooth Lock	A washer with external teeth. Used to prevent nuts and bolts from backing out.
	Internal Tooth Lock	A washer with internal teeth. Used to prevent nuts and bolts from backing out.
	Square	A square shape washer.
	Dock	Dock washer have a larger outside diameter and are thicker than standard.
	Ogee	Thick, larger diameter, cast iron washers with a curved or sculpted appearance. Typically used in dock and wood construction.

Air Conditioner Capacity Measurement

Capacity of an Air Conditioner always measure on ton. You can hear 1ton or 3 ton AC. We know that ton is a measuring unit of mass. So, this question must be arise on your mind, why the capacity of an Air Conditioner measuring in ton??!! Now, before getting the answer of your question, I want to review some old school topics.

There are two measuring system using world wide – Metric System and Imperial System. I am not going to describe these systems.

Now,

1 ton = 2204.62 lb = 1000 Kg

1 short tone = 2000 lb = 907.185 KG

For Temperature,

0˚C = 32˚F = 273 K

100˚C = 212˚F = 373K

Current Transformer

A Current Transformer (CT) is an electric component that produced an alternating current in its secondary coil which is proportional to the AC in its primary coil. Current Transformers are known as instrument transformer, which are designed for measurement. Current Transformers using in an electrical line with high current or high voltage where current or voltage directly measurement is too risky. CT gives a lower amount of current with its secondary which is proportional to the current in the primary. This lower amount of current is suitable for measuring instruments. Current Transformers are broadly used for metering and protective relays in the electrical power industry.

A CT is applying where we need to measure line / Phase current. It is some time difficult to measure directly for high current or high voltage of the circuit. A CT provides an isolated lower current in its secondary coil to the ammeter for showing the measuring value. This lower current is proportional to the current in the primary circuit and it is suitable for measuring instruments. Current transformer widely used in electrical power industry for measuring, billing and protective relays.