Star and Delta Wiring in 3 Phase Systems
A three phase circuit uses three alternating currents to supply power. It stems from three coils placed 120° apart, they rotate in a sinusoidal waveform magnetic field. Three phase circuits are commonly used in industrial equipment where higher power output is required.
Star (or ‘Y’ / ‘wye’) Connection
A star connection has 3 conductors (or in our case elements) connected to a load at one terminal and the other terminal end of each element is connected to a neutral point.
The Neutral Point is used to help manage the loads that are not perfectly balanced. The star connection of the three phases and a neutral connection, allows the use of two voltages. These are identified as the phase voltage and the line voltage.
Line Voltage
Line voltage refers to the voltage between two lines in a three phase configuration.
Phase Voltage
Phase Voltage is the voltage measured across a single component (or element).
In Star set ups, the line voltage is always higher than the phase voltage. In the UK the standard is 240/415V for star.
Example 1 – Star
For the above circuit, we have three Elements wired in Star for an immersion heater ran on 240/415V.
- Each Element is 57.6Ω
- L1 Connects to element 1
- L2 connects to element 2
- L3 connects to element 3
- N is the Neutral connection to all elements.
- Phase Current = 4.17A
- Line Voltage = 415V
Phase Voltage Calculation
Line Voltage Calculation
Line Current and Phase Current Calculation
The line current and the phase current in STAR configuration are equal to one another.
Wired as above, this immersion heater would be operating as a 3kW 240/415V.
How does this look in practice?
For reference, in our FI Immersion Heaters, when a customer will be connecting in STAR. We will connect the terminals with a link for the neutral.
Delta Δ (or mesh) Connection
A delta connection has no neutral point, the conductors (elements) are connected in a loop with the supply, where the end of one load is connected to the start of the next load.
Only a single magnitude of voltage can be achieved by using the Delta Connection.
Example 2 – Delta
For the above circuit, we have three Elements wired in delta for an immersion heater ran on 415V.
- Each Element is 57.6Ω
- L1 Connects to element 1
- L2 connects to element 2
- L3 connects to element 3
- Phase Current = 7.20A
- Line Voltage = 415V
Line Voltage and Phase Voltage Calculation
In a balanced delta configuration the line voltage and the phase voltage will be equal to each other as each conductor is connected directly.
Line Current and Phase Current Calculation
The Line Current for the delta configuration will be the resultant of the two joining phase currents as below.
Wired as above, this immersion heater would be operating as a 9kW 415V.
How does this look in practice?
For reference, in our FI Immersion Heaters, when a customer will be connecting in DELTA. We will connect the terminals with 3 Links to ensure all elements are linked within the loop and connected to the power supply.
Let’s Compare
| Star | Delta |
|---|---|
| All coils are connected to a neutral point and voltage is shared. | No Neutral – all coils are connected to one another in a ‘closed loop’. |
| Line Voltage is higher than phase voltage. | Line Voltage and Phase Voltage is the same. |
| Line Current and Phase Current are the same. | Line current is higher than the phase current. |
| Fits applications that need lower starting currents. | Fits industrial applications needing heavier load from start up. |
| Deemed more efficient to begin with as it will have a slower start up. Used in Long Distance Power Transmission. | Deemed less efficient on start ups, but more effective at taking higher power for longer durations. |
In order for our team to offer the most suitable heater, please advise on your applications requirements.
Upon installing and wiring components into an application, this should be checked and verified by a qualified electrician. Local or site-specific wiring codes and regulations should be adhered to at all times.
