Voltage Units

Voltage is the "electrical pressure" that pushes electrons through a circuit. It's essential for understanding compressor power.

What is Voltage?

Voltage ($V$) is the electrical potential difference between two points. Think of it as:

• Water pressure in a pipe → Voltage in a wire
• Higher pressure = more force to move water
• Higher voltage = more force to move electrons

Voltage Units

Unit	Symbol	Equivalence
Volt	V	Base unit
Kilovolt	kV	1,000 V
Millivolt	mV	0.001 V

Common Industrial Voltages

Single Phase

Voltage	Application
120V	Small tools, lighting (Americas)
220-240V	Residential, small equipment

Three Phase

Voltage	Application
208V	Light commercial (Americas)
220-240V	Small industrial
380-415V	Standard industrial (Europe, Latin America)
440-480V	Heavy industrial (Americas)
600V	Heavy industrial (Canada)

Voltage and Compressors

Why Three Phase?

Industrial compressors use three-phase power because:

1. Higher efficiency - Less transmission losses
2. Smaller motors - For the same power
3. Smoother starting - No extreme current spikes
4. Lower wiring cost - Thinner cables

Voltage-Current-Power Relationship

Single phase:

$$P = V \times I \times \cos\phi$$

Three phase:

$$P = \sqrt{3} \times V \times I \times \cos\phi = 1.732 \times V \times I \times \cos\phi$$

Where:

• $P$ = Power (W)
• $V$ = Voltage (V)
• $I$ = Current (A)
• $\cos\phi$ = Power factor

Rule of Thumb

Higher voltage means lower current for the same power. Lower current = thinner cables = lower cost.

Voltage Drop

Voltage drop in long cables affects performance:

Voltage Drop	Effect
< 3%	Acceptable
3-5%	Efficiency reduction
> 5%	Motor overheating

Drop Calculation

$$\Delta V (\%) = \frac{L \times I \times K}{V \times A} \times 100$$

Where:

• $L$ = Cable length (m)
• $I$ = Current (A)
• $K$ = Material constant
• $A$ = Conductor area (mm²)

Important

A 10% voltage drop can reduce motor life by 50%.

System Conversion

From	To	Factor
380V three-phase	220V phase-neutral	$\div \sqrt{3}$
480V three-phase	277V phase-neutral	$\div \sqrt{3}$