Practical Transformer Terms Explained
Boardman Transformers manufactures standard and custom-built transformers for industrial, commercial, OEM and specialist electrical applications.
This glossary explains common transformer terms used across control transformers, industrial transformers, auto transformers, transformer enclosures and custom-built transformer specifications.
Use this page as a practical guide when reviewing transformer requirements, comparing product ranges or preparing information for a transformer enquiry.
Transformer Types
Transformer
A transformer is an electrical device used to transfer electrical energy between circuits, usually by changing voltage from one level to another.
Transformers are used in control panels, machinery, industrial equipment, power systems, automation systems and specialist electrical applications.
Boardman Transformers manufactures a wide range of standard and custom-built transformers for industrial, commercial, OEM and specialist requirements.
Related page:
View Transformer Manufacturer UK
Control Transformer
A control transformer is used to provide suitable control voltages for industrial control panels, machinery and automation systems.
Control transformers are commonly used to supply control circuits, contactors, relays, panel controls, signalling equipment and automation devices.
Boardman manufactures several control transformer ranges, including SCL, MCL, CL and cCSAus C Range transformers for different rating, voltage and compliance requirements.
Related page:
View Control Transformers
Control Circuit Transformer
A control circuit transformer is a transformer designed specifically for control circuit applications.
It is typically used to step voltage down to a safer or more suitable control voltage, such as 24V, 48V, 110V or another specified secondary voltage.
Control circuit transformers are widely used in industrial control panels, machinery controls, panel building and automation systems.
Related page:
View Control Transformers
Industrial Transformer
An industrial transformer is designed for machinery, equipment, production environments, control panels and wider industrial electrical systems.
Industrial transformers may be single phase or three phase and can be supplied across a range of ratings, voltage configurations and installation requirements.
Boardman manufactures industrial transformers for standard applications and can also support custom-built industrial transformer requirements.
Related page:
View Industrial Transformers
Three Phase Transformer
A three phase transformer is designed for three phase electrical systems, which are commonly used in industrial and commercial power applications.
Three phase transformers are often used with machinery, production equipment, plant installations and larger electrical systems requiring reliable voltage transformation.
Boardman manufactures three phase industrial transformers, including 3CL ranges for different power ratings.
Related page:
View Industrial Transformers
Single Phase Transformer
A single phase transformer is designed for single phase electrical systems.
Single phase transformers are commonly used in control panels, machinery, equipment, commercial installations and specialist electrical applications where single phase voltage transformation is required.
Boardman manufactures single phase control, industrial and custom-built transformer solutions.
Related page:
View Control Transformers
Auto Transformer
An auto transformer uses a single winding to provide voltage transformation.
Auto transformers are commonly used where voltage step-up or step-down is required and full electrical isolation is not necessary.
Boardman manufactures single phase and three phase auto transformers for industrial, commercial and specialist electrical applications.
Important note: auto transformers do not provide full electrical isolation between input and output. If isolation is required, an isolating transformer may be more suitable.
Related page:
View Auto Transformers
Auto Starter Transformer
An auto starter transformer is designed for reduced-voltage motor starting applications.
It is used as part of a motor starting system to reduce the voltage applied to a motor during start-up. This can help control starting current and reduce electrical and mechanical stress during motor starting.
Auto starter transformers are different from general auto transformers. An auto transformer is used for voltage conversion, while an auto starter transformer is specifically used for motor starting.
Related page:
View Auto Starter Transformers
Isolation Transformer
An isolation transformer uses separate primary and secondary windings to provide electrical separation between circuits.
Isolation transformers are used where circuit separation, safety, noise reduction or system protection is required.
Unlike an auto transformer, an isolation transformer provides electrical isolation between input and output.
Related page:
View Control Transformers
Double-Wound Transformer
A double-wound transformer has separate primary and secondary windings.
This construction provides separation between the input and output circuits and is commonly used in control transformers, isolation transformers and industrial transformer applications.
Double-wound construction is often selected where electrical isolation is required.
Related page:
View Industrial Transformers
Custom-Built Transformer
A custom-built transformer is manufactured to suit specific voltage, rating, mounting, connection, enclosure or application requirements where a standard transformer range is not suitable.
Custom-built transformers may be required for non-standard voltages, specialist machinery, OEM equipment, unusual mounting arrangements, specific compliance requirements or demanding installation environments.
Boardman manufactures custom-built transformers for industrial, commercial, OEM and specialist electrical applications.
Related page:
View Custom Built Transformers
Bespoke Transformer
A bespoke transformer is another term for a custom-built transformer.
It means the transformer is designed or manufactured around a specific project requirement rather than selected directly from a standard range.
Bespoke transformers may include custom voltages, ratings, enclosures, terminations, mounting arrangements or documentation requirements.
Related page:
View Custom Built Transformers
Transformer Enclosure
A transformer enclosure is a protective housing used to support safe and practical transformer installation.
Enclosures can help protect transformers from physical contact, environmental conditions and installation risks while also supporting ventilation and access requirements.
Boardman supplies transformer enclosures for single phase, three phase and larger industrial transformer installations.
Related page:
View Transformer Enclosures
Ratings and Electrical Terms
VA
VA stands for volt-amperes.
It is a unit used to describe the apparent power rating of a transformer, especially on smaller transformers such as control circuit transformers.
For example, a 100VA transformer can supply a certain combination of voltage and current within its rated capacity.
kVA
kVA stands for kilovolt-amperes.
One kVA equals 1,000VA. It is commonly used for larger transformer ratings.
Industrial transformers, three phase transformers and larger custom-built transformers are often specified in kVA.
MVA
MVA stands for megavolt-amperes.
One MVA equals 1,000kVA. It is used for very large transformer ratings.
MVA ratings are normally associated with larger power transformer applications.
Transformer Rating
A transformer rating describes the amount of electrical load the transformer is designed to supply.
Ratings may be shown in VA, kVA or MVA depending on transformer size.
Choosing the correct rating is important. A transformer should be selected based on voltage, current, phase, frequency, load type, duty cycle, environment and any required safety margin.
Load
Load refers to the equipment or electrical demand connected to the transformer output.
The type of load affects transformer selection. For example, control circuits, motors, heaters, power supplies and machinery may each have different starting, running or duty requirements.
Load Current
Load current is the amount of current drawn by the connected equipment.
Knowing the load current helps determine the required transformer rating.
For a quote, it is useful to provide the expected load current, output voltage and whether the application is single phase or three phase.
Inrush Current
Inrush current is the initial current drawn when equipment is first energised.
Some loads draw a much higher current at start-up than during normal running. This can affect transformer selection and protection requirements.
Applications with high inrush current may require special consideration when specifying transformer rating and circuit protection.
Duty Cycle
Duty cycle describes how often and how long a transformer or connected load operates.
Some transformers operate continuously, while others operate intermittently. Duty cycle can affect heating, rating, protection and transformer selection.
For custom or specialist transformer enquiries, duty cycle information is useful.
Continuous Duty
Continuous duty means the transformer is designed to operate continuously at its rated load under specified conditions.
Many industrial transformers are designed for continuous duty, but the correct transformer should always be selected based on rating, application and installation environment.
Frequency
Frequency refers to the alternating current supply frequency, usually measured in hertz.
Common frequencies include 50Hz and 60Hz.
The required frequency should be confirmed when specifying a transformer, especially for international, export or specialist applications.
Power Factor
Power factor describes the relationship between real power and apparent power in an electrical system.
It can affect transformer sizing, especially in applications with motors, inductive loads or complex electrical equipment.
For many transformer enquiries, the load type and power factor may help confirm the correct rating.
Voltage and Phase Terms
Primary Voltage
Primary voltage is the voltage supplied to the transformer input winding.
When requesting a transformer quote, the primary voltage should be provided clearly.
Examples may include 230V, 400V, 415V or another specified voltage depending on the application.
Secondary Voltage
Secondary voltage is the voltage provided by the transformer output winding.
The required secondary voltage depends on the equipment or control circuit being supplied.
Common secondary voltages for control applications may include 12V, 24V, 48V, 110V and 230V, depending on the transformer range and specification.
Input Voltage
Input voltage is another term for the voltage supplied to the transformer.
It is usually the same as primary voltage.
For enquiries, include the input voltage and whether the supply is single phase or three phase.
Output Voltage
Output voltage is another term for the voltage supplied by the transformer to the load.
It is usually the same as secondary voltage.
For enquiries, include the required output voltage and the load it will supply.
Step-Down Transformer
A step-down transformer reduces voltage from a higher input voltage to a lower output voltage.
Step-down transformers are commonly used in control panels, machinery, automation systems and industrial equipment where a lower control or equipment voltage is required.
Step-Up Transformer
A step-up transformer increases voltage from a lower input voltage to a higher output voltage.
Step-up transformers may be used in specialist applications where equipment requires a higher voltage than the available supply.
Voltage Tapping
Voltage tappings are connection points on a transformer winding that allow different voltage options or adjustments.
Tappings can help match transformer output or input requirements to the available supply or required load voltage.
Different transformer ranges may offer different tapping arrangements.
Single Phase
Single phase refers to an electrical supply using one alternating voltage waveform.
Single phase transformers are commonly used in control circuits, smaller industrial applications, commercial systems and specialist equipment.
Three Phase
Three phase refers to an electrical supply using three alternating voltage waveforms.
Three phase supplies are common in industrial and commercial power systems because they are suitable for larger machinery, motors and industrial equipment.
Three phase transformers are often used in production environments, plant installations and larger electrical systems.
Neutral
Neutral is a conductor that can provide a return path in an electrical system.
Transformer neutral arrangements depend on the transformer design, winding configuration and application.
If a neutral connection is required, it should be specified clearly during enquiry.
Star Connection
A star connection is a three phase winding connection arrangement.
It may also be referred to as a wye connection. Star configurations are used in many three phase transformer and electrical system applications.
Specific winding connections should be confirmed when specifying a transformer.
Delta Connection
A delta connection is another three phase winding connection arrangement.
Delta connections are commonly used in three phase electrical systems and may be required depending on supply, load and application requirements.
Specific winding connections should be confirmed when specifying a three phase transformer.
Construction and Protection
Winding
A winding is the coil of wire used in a transformer to transfer electrical energy through electromagnetic induction.
Transformers usually include primary and secondary windings, unless they are auto transformers, which use a shared winding arrangement.
Primary Winding
The primary winding is the transformer winding connected to the input supply.
It receives electrical energy from the supply and transfers it magnetically to the secondary winding.
Secondary Winding
The secondary winding is the transformer winding connected to the output load.
It provides the required output voltage to the connected circuit or equipment.
Earth Screen
An earth screen is a conductive screen placed between transformer windings.
It can help improve safety and reduce electrical interference between primary and secondary circuits.
Some Boardman transformer ranges include an earth screen between primary and secondary windings.
Insulation Class
Insulation class describes the temperature rating of the insulating materials used in a transformer.
Common classes include Class B, Class F and Class H.
The correct insulation class depends on transformer design, operating temperature, environment and application.
Temperature Rise
Temperature rise refers to the increase in transformer temperature above ambient temperature during operation.
Transformer design, load, ventilation, duty cycle and installation environment can all affect temperature rise.
Ambient Temperature
Ambient temperature is the temperature of the surrounding environment where the transformer operates.
It is important because high ambient temperatures can affect transformer performance, cooling and lifetime.
If the transformer will operate in unusual temperature conditions, this should be included in the enquiry.
Cooling
Cooling refers to how heat is removed from a transformer during operation.
Many dry-type transformers rely on natural air cooling. Enclosed transformers may require suitable ventilation to maintain safe operation.
The installation environment and enclosure type should be considered when specifying a transformer.
Ventilation
Ventilation allows heat to escape from a transformer or transformer enclosure.
Ventilated transformer enclosures are commonly used where airflow is needed to support transformer cooling.
If environmental protection is required, the balance between ventilation and IP rating should be considered.
Terminals
Terminals are the connection points used to connect cables to the transformer.
Different transformer ranges may include different terminal arrangements. For custom applications, termination requirements should be specified during enquiry.
Touch-Proof Terminals
Touch-proof terminals are designed to reduce the risk of accidental contact with live parts.
They are often used in control transformer and panel applications where practical installation and user safety are important.
Mounting
Mounting refers to how the transformer is physically installed.
Transformers may require foot mounting, panel mounting, enclosure mounting or other arrangements depending on the product range and application.
Mounting requirements should be included when requesting a quote.
Enclosed Transformer
An enclosed transformer is supplied within a protective enclosure.
Enclosures may be selected for physical protection, installation requirements, environmental protection, safety or site requirements.
Boardman supplies transformer enclosures for single phase, three phase and large industrial transformer applications.
Related page:
View Transformer Enclosures
Open Transformer
An open transformer is supplied without a complete protective enclosure.
Open transformers may be installed inside control panels, electrical assemblies or suitable protected environments.
When using an open transformer, installation protection and access safety should be considered.
Circuit Protection
Circuit protection helps protect the transformer and connected circuits from fault conditions.
This may include fuses, circuit breakers or other protective devices.
The correct protection depends on transformer rating, inrush current, primary voltage, secondary load and application requirements.
Primary Protection
Primary protection is protection installed on the transformer input side.
It helps protect the transformer and supply circuit against faults or overload conditions.
Primary protection should be selected based on transformer rating, inrush current and applicable requirements.
Secondary Protection
Secondary protection is protection installed on the transformer output side.
It helps protect the secondary circuit and connected load.
The need for secondary protection depends on the transformer, load and circuit design.
Standards and Compliance
IEC / BS-EN 61558
IEC / BS-EN 61558 is a standard commonly associated with safety requirements for transformers, power supplies and similar equipment.
Several Boardman transformer ranges are designed and manufactured to comply with IEC / BS-EN 61558 requirements.
The applicable standard depends on the product type and specification.
IEC 60076
IEC 60076 is a standard series relating to power transformers.
It may be relevant for larger industrial transformers and three phase transformer applications.
Where standards are important to a project, requirements should be confirmed during enquiry.
cCSAus
cCSAus is a certification mark indicating compliance with applicable Canadian and U.S. safety requirements.
Boardman manufactures cCSAus C Range control transformers for applications requiring recognised certification for U.S. and Canadian markets.
Related page:
View cCSAus Control Transformers
UL5085
UL5085 is a standard relating to low voltage transformers for U.S. market applications.
It is relevant to certain certified transformer products and applications requiring recognised compliance for North American markets.
If your project requires UL or CSA-related compliance, include this information in your enquiry.
CE Marking
CE marking indicates that a product meets applicable European requirements.
Whether CE marking applies depends on the product, specification and applicable legislation.
For projects requiring specific documentation or compliance, requirements should be confirmed during enquiry.
UKCA Marking
UKCA marking is used for certain products placed on the market in Great Britain.
If UKCA marking or related documentation is required for a project, this should be included in the transformer enquiry.
Compliance Documentation
Compliance documentation may include declarations, test information, certification references, datasheets or other technical documents.
The required documentation depends on the transformer type, project requirements and applicable standards.
If documentation is required, include this in the enquiry.
Enclosures and IP Ratings
IP Rating
An IP rating describes the level of protection an enclosure provides against solid objects and water ingress.
For transformer enclosures, IP rating is important because it affects where and how the transformer can be installed.
Boardman transformer enclosures are available with standard IP23 rating, with IP54 and IP65 options available on request depending on the application..
IP21
IP21 is an enclosure protection rating commonly used for indoor electrical equipment where basic protection against solid objects and vertically falling water droplets is required.
Suitable for clean, dry indoor environments where ventilation and practical installation are more important than higher environmental protection.
IP23
IP23 is an enclosure protection rating commonly used for ventilated indoor applications.
It provides a level of protection while allowing ventilation for heat dissipation.
IP54
IP54 provides increased protection against dust and water splashes compared with IP23.
IP54 transformer enclosure options may be suitable where additional environmental protection is required.
Availability depends on the enclosure type and application requirements.
IP65
IP65 provides a higher level of dust and water protection.
IP65 transformer enclosure options may be required for more demanding environments where increased protection is necessary.
When requesting an IP65 enclosure, provide details of the installation environment and transformer requirements.
Sheet Steel Enclosure
A sheet steel enclosure is a protective enclosure manufactured from steel sheet.
Boardman transformer enclosures use sheet steel construction with a durable finish suitable for industrial and commercial installations.
Epoxy Powder Coated Finish
An epoxy powder coated finish is a durable protective coating applied to metal surfaces.
Boardman transformer enclosures are finished in hammer grey epoxy powder coating to support long-lasting protection and a professional finish.
Hammer Grey Finish
Hammer grey is the standard finish used on many Boardman transformer enclosures.
It provides a durable industrial appearance suitable for electrical and transformer installations.
Wall Mounted Enclosure
A wall mounted enclosure is designed to be fixed to a wall or suitable vertical surface.
Wall mounted transformer enclosures can be useful where floor space is limited or where the installation requires elevated positioning.
Floor Mounted Enclosure
A floor mounted enclosure is designed to sit on the floor or suitable base.
Floor mounted transformer enclosures are often used for larger or heavier transformer installations.
Specification and Enquiry Terms
Transformer Specification
A transformer specification defines the electrical, mechanical, environmental and compliance requirements for the transformer.
A useful transformer specification may include input voltage, output voltage, phase, rating, frequency, load type, duty cycle, mounting, enclosure and documentation requirements.
Primary and Secondary Voltage Requirements
Primary and secondary voltage requirements describe the input and output voltages needed for the transformer.
These are two of the most important details required for transformer selection or quotation.
Phase Requirement
Phase requirement describes whether the transformer is single phase or three phase.
This should be confirmed during enquiry because it affects transformer design, rating and application suitability.
Rating Requirement
Rating requirement describes the required VA, kVA or MVA rating.
The rating should be based on the connected load, duty cycle, inrush current and any required safety margin.
Mounting Requirement
Mounting requirement describes how the transformer needs to be installed.
Examples include foot mounting, panel mounting, wall mounting, floor mounting or enclosure mounting.
Mounting requirements are especially important for custom-built transformers and enclosure selections.
Enclosure Requirement
Enclosure requirement describes whether the transformer needs to be supplied with a protective housing.
Useful details include indoor or outdoor use, required IP rating, ventilation needs, cable entry requirements and mounting arrangement.
Quantity Required
Quantity required is the number of transformers or enclosures needed.
This helps with pricing, lead time and manufacturing planning.
Lead Time
Lead time is the expected time between order placement and supply.
Lead time depends on transformer type, rating, quantity, material availability, custom requirements and current manufacturing workload.
For urgent requirements, contact Boardman Transformers directly.
Custom Voltage
A custom voltage is a primary or secondary voltage that does not match a standard transformer range.
Boardman can manufacture custom transformers to suit non-standard voltage requirements depending on the application and specification.
Custom Rating
A custom rating is a transformer VA, kVA or MVA rating selected to suit a specific application.
Custom ratings may be required when standard products do not match the load, duty cycle or installation requirements.
OEM
OEM stands for Original Equipment Manufacturer.
OEMs often require transformers built into machinery, systems or equipment as part of a larger product or installation.
Boardman supports OEMs with standard and custom transformer solutions.
Panel Builder
A panel builder manufactures electrical control panels or electrical assemblies.
Panel builders commonly use control transformers, industrial transformers, auto transformers and transformer enclosures in their projects.
Boardman supplies transformer solutions suitable for panel building and control panel applications.
Machinery Manufacturer
A machinery manufacturer builds machinery or industrial equipment.
Machinery manufacturers may require control transformers, auto transformers, industrial transformers, auto starter transformers or custom-built transformers depending on their equipment requirements.
Electrical Contractor
An electrical contractor installs or maintains electrical systems.
Electrical contractors may require transformer products for industrial, commercial, machinery, panel or site applications.
Technical Support
Technical support means practical help with transformer selection, specification or application requirements.
Boardman Transformers can help review voltage, rating, phase, enclosure and application details to identify a suitable transformer option.
Common Transformer Questions
What information should I provide for a transformer quote?
To help Boardman Transformers provide an accurate quotation, include as much of the following information as possible:
Primary voltage
Secondary voltage
Single phase or three phase
Required VA, kVA or MVA rating
Frequency
Load type
Duty cycle
Mounting requirements
Enclosure requirements
IP rating if required
Quantity
Compliance or documentation requirements
If you are unsure, contact the Boardman team and we can help identify the information required.
What is the difference between a standard transformer and a custom-built transformer?
A standard transformer is selected from an existing product range.
A custom-built transformer is manufactured to suit specific voltage, rating, connection, mounting, enclosure or application requirements.
Custom-built transformers are useful when a standard range does not match the project specification.
What is the difference between an auto transformer and an isolating transformer?
An auto transformer uses a shared winding arrangement and is used for voltage step-up or step-down where electrical isolation is not required.
An isolating transformer uses separate primary and secondary windings to provide electrical separation between circuits.
If isolation is needed for safety, system separation or noise reduction, an isolating transformer may be more suitable.
What is the difference between an auto transformer and an auto starter transformer?
An auto transformer is used for general voltage conversion where isolation is not required.
An auto starter transformer is used specifically for reduced-voltage motor starting applications.
Although the names are similar, the applications are different.
What is the difference between a control transformer and an industrial transformer?
A control transformer is typically used to supply control circuits, panels, relays, contactors and automation systems.
An industrial transformer is a broader category used for machinery, equipment, production environments, power systems and specialist industrial applications.
Some projects may use both control and industrial transformers.
What is the difference between single phase and three phase transformers?
A single phase transformer is used with single phase electrical systems.
A three phase transformer is used with three phase systems, which are common in industrial and commercial applications.
The correct choice depends on the supply, load and application.
Need Help With a Transformer Specification?
If you are unsure which transformer type, rating, voltage or enclosure is suitable for your application, Boardman Transformers can help.
Our team supports customers with standard transformer ranges, custom-built transformers, industrial transformer applications, auto transformers, control transformers and transformer enclosures.