Designed & manufactured in Great Britain
+44 (0) 1443 813500 sales-uk@hotset.com
Hotset

Electrical guide

Understanding
phase configurations

Single phase, line-to-line, star, open wye and delta arrangements place different voltages across each heating element. Correct selection is essential for the intended heat output and safe operation.

The basic principle

The element voltage determines the heat

The supply voltage and the way the elements are connected determine the voltage across each element. Applying the wrong voltage can cause a major change in wattage because resistive heater power is proportional to voltage squared.

PowerP = V × I
ResistanceR = V² ÷ P
Balanced 3 phaseP = √3 × VL × IL
UK supply example: a typical three-phase supply is approximately 400 V between phases and 230 V from a phase to neutral. Always confirm the actual site supply and control arrangement before manufacture or connection.

Common heater arrangements

Five useful configurations

LN
Single phase

One supply circuit

A heating element or group of elements is connected across a single supply voltage, commonly live to neutral at approximately 230 V.

  • Simple connection and control
  • Common for lower-power heaters
  • Element voltage equals the applied supply voltage
L1L2
“2 phase” / line-to-line

Connected across two live phases

Hotset commonly describes this as 2 phase: one heater circuit connected between two phases of a three-phase supply, normally receiving approximately 400 V line-to-line.

  • No neutral connection
  • Element is designed for the full line-to-line voltage
  • Electrically this remains a single-phase load
L1 L2 L3 N
Three phase wye / star

Three elements share a star point

One end of each element is joined at a common star point. With a neutral connected, the star point is tied to the supply neutral.

  • Each element sees line voltage ÷ √3
  • On 400 V three phase, each element sees about 230 V
  • Neutral can accommodate imbalance where the system is designed for it
L1 L2 L3 NO NEUTRAL
Three phase open wye

Star connected without neutral

The three elements are joined at a common star point, but no neutral is connected. With equal element resistances, the load remains balanced and the star point floats at the electrical centre.

  • Three live connections only
  • Each balanced element sees approximately line voltage ÷ √3
  • Resistance is normally checked across any two live terminals
L1 L2 L3 EACH ELEMENT RECEIVES FULL LINE VOLTAGE
Three phase delta

Each element connects between two phases

The three elements form a closed triangle. Each element is connected directly across a pair of phases and therefore receives the full line-to-line voltage.

  • On a 400 V supply, each element receives 400 V
  • No neutral connection
  • Element resistance must be designed for the full line voltage

At a glance

How the arrangements compare

Configuration Connections Voltage across each element Neutral
Single phase L + N, or two supply conductors Applied supply voltage Usually, when connected L–N
“2 phase” / line-to-line L1 + L2 Line-to-line voltage No
Three-phase wye / star L1 + L2 + L3 + N VL ÷ √3 Yes
Three-phase open wye L1 + L2 + L3 VL ÷ √3 when balanced No
Three-phase delta L1 + L2 + L3 Full line-to-line voltage No
Terminology note: “2 phase” is widely understood in heater workshops to mean a load connected across two phases. It is not the same as the historical true two-phase electrical supply system.

Interactive calculator

Phase configuration calculator

Select the heater configuration and enter the supply voltage. Change any white calculation field and the remaining values will update automatically.

Electrical calculation

Heater phase values

OPEN WYE
Three elements connected in star without neutral

Each element receives the line voltage divided by √3. A resistance measurement between two live terminals passes through two elements in series.

Important: Calculated values assume a balanced resistive load with three equal heating elements. Measurements must only be taken with the heater safely isolated from the electrical supply and control equipment.

Testing a disconnected heater

What a resistance measurement represents

Resistance checks must be made only with the heater safely isolated from the electrical supply and any controller. The reading seen at the terminals depends on the internal connection.

Single phase or line-to-line Reading = R

The meter measures the resistance of the connected heater circuit directly.

Three-phase star, live to neutral Reading = Relement

Measure from each live terminal to the accessible neutral point. Each reading represents the resistance of one individual Phase

Open wye, line to line Reading = 2Relement

With no neutral connection available, the meter passes through two equal heating elements in series via the common star point.

Delta, line to line Reading = ⅔Relement

One element is measured in parallel with the other two elements connected in series.

Useful three-phase checks: For a star heater with neutral, measure L1–N, L2–N and L3–N. For an open-wye heater, measure L1–L2, L2–L3 and L1–L3. With three equal, healthy elements, the three readings in either arrangement should be approximately equal. A significant difference indicates that an element or connection requires investigation.

Preparing an enquiry

What Hotset needs to know

Supply voltage

State both the available line-to-line and line-to-neutral voltage where known.

Configuration

Single phase, line-to-line “2 phase”, star with neutral, open wye or delta.

Total wattage

Give the total heater power—not only the wattage of one internal element.

Terminal arrangement

Identify the number of terminals, links, cables and any accessible star point.

Control method

Contactor, solid-state relay, thyristor controller or another switching arrangement.

Existing information

Include a drawing, wiring diagram, nameplate photograph or resistance readings where available.

Unsure which connection is required?

Send us the supply and heater details.

Hotset can help establish the correct element voltage, resistance and connection arrangement for the application.

Discuss your heater →
Safety: Three-phase equipment can present lethal voltages. Installation, isolation and testing must be carried out by a suitably qualified person in accordance with the equipment documentation and applicable regulations.