What is an Isolation Transformer?

Transformers transfer required signals and power across the separated circuits through magnetic flux while physically and electrically isolating circuitry from unwanted currents,

Although any transformer consisting of two separate coils and no grounding shields provide isolation, the best isolation transformers are especially designed for providing electrical isolation, whose primary purpose is to isolate an AC source from circuits, devices, and equipment.

Best Isolation transformers serve three main purposes: isolating the secondary from the ground (earth); providing step up or step down of line or mains voltages; reducing line noise being transmitted from the primary to the secondary or vice versa.

Isolates Secondary from Ground (Earth)

An isolation transformer is used to prevent an unconditioned ground connection between the primary and secondary and prevent high-voltage discharge. Through such separation, it eliminates ground loops and inadvertent test equipment grounding. 

In single-phase distribution, where multiple, physically-separated devices share a common power line, ground loops are created due to different ground potentials of the devices. These ground loops cause problems in medical devices and can be troublesome during device tests. 

Designers find it difficult to measure ground loops with devices that use rectified line voltages where AC supply is converted into DC supply. Grounded test equipment like oscilloscopes can inadvertently short power supplies in these devices.

When using an oscilloscope to measure signals in an electrical circuit that is not galvanically isolated from the network, isolation transformers must be used. This is because the current circuit can be closed (short-circuited) between the oscilloscope common point and grounding. 

When equipment under test is powered by an isolating transformer, its ground (equipment ground) is separated from the earth ground; the transformer isolates the device under test from the common supply ground.

A person working on the equipment (standing at earth ground) cannot accidentally provide a path to the ground should they make contact with the circuit. This makes the setup safer for users, eliminating the possibility of a shock.

Provides Step Up or Down of Line or Mains Voltages

Basically, isolation transformers are transformers. Transformers are electromagnetic devices that transform alternating current (AC) electrical energy from primary to secondary side. 

The transformer core magnetic field transforms the energy with equal frequency and approximately equal power. Thus, transformers provide galvanic isolation in the electrical system.

Isolation transformers operate in the same way as transformers except their main task is to provide galvanic isolation in the electrical system.

They can work as step-up or step-down transformers but often operate with turns ratio of 1:1, that is, with the same number of turns on the primary and secondary windings. That is, the primary and secondary voltage values are equal. 

Isolation transformers used for safety usually have a turns ratio of 1:1 but step-up and step-down isolation transformers are used when the voltage also needs to be changed.  

For example, isolation transformers are used as instrument transformers for measuring the high voltage. High voltage is both dangerous to the person measuring and the measurement circuits. In this case, the step-down isolation transformer reduces the high voltage to the safe level and measurement range.

Reduces Line Noise Being Transmitted from Primary to Secondary or Vice Versa

The isolation transformer is used for breaking a circuit into primary and secondary so that direct current (DC) noise does not get through. It prevents capacitance build-up by high-frequency noise from AC power lines, which cause problems for sensitive transducers and instruments.

Isolation transformers are built with electrostatic shields which additionally increase the electrical noise suppression.

Windings capacitance in isolation transformers create capacitive coupling. This enables AC signals to pass from primary to the secondary side which significantly increases the noise level. To counter this, the windings are surrounded by a metal strip which is grounded, creating a Faraday shield.

Three-Phase and Shielded Isolation Transformer

A three-phase isolation transformer is a 3-phase transformer and has isolated primary and secondary windings. Thus, the power input and output are also isolated.

A shielded 3-phase transformer is more efficient than the standard one and provides protection for sensitive equipment.

Shielded isolation transformers possess all the features of standard isolation transformers but have a full copper or aluminum shielding between the primary and the secondary windings.

The electrostatic shielding helps reduce the effects of power surges by isolating electrical power from the normal power supply source.

When multiple shielded 3-phase isolation transformers are installed between the source and the load, it is known as cascading and improves power quality.

Double Isolation

Double isolation is implemented by putting a metallic safety shield between the primary and secondary windings and then connecting it to the ground. This way the electricity will flow to the ground in case of isolation damage, providing safety.

Another method of implementing double isolation is through reinforced insulation made up of multiple layers. In this case, if one layer breaks the next layer will provide required safety.

Benefits of Isolation Transformers

Isolation transformers benefit individuals, equipment, and organizations.


Isolation transformers provide high-levels of safety to electrical appliances from power issues. Sudden shocks and voltage fluctuations can damage parts or components of the equipment and disrupt their normal functioning.

Isolation transformers separate such equipment from the power source to prevent such risks.They help to save them and elongate their qualitative life-span.

Hospitals and healthcare centers use sensitive medical equipment for diagnostics, treatments, etc. Doctors, nurses, and patients may all be susceptible to sudden damages of such equipment during power voltage problems.

Reduced Surges

Power surges have devastating effects on power-based appliances. Though such voltage spikes occur for a short period, they can severely damage the equipment. 

Isolation transformers protect the equipment through galvanic isolation while reducing the surges. Generally, they isolate DC power signals and so there is no chance of equipment damage due to surges.

Noise Reduction

Often certain noise disturbances are evident from audio speakers when signals from amplifiers reach the speakers’ output circuit. Isolation transformers mitigate such audio problems. 

Isolation transformers are designed to include Faraday shields, which block the electric field if there are any interruptions in the power flow. Any electromagnetic noise present in the equipment will be reduced.

Isolation transformers are helpful in many industries. Specifically, telecommunication equipment, CNC machines, and remote control equipment require reliable isolation transformers.

Improved Power Quality

The Faraday shields of isolation transformers improve efficiency. They decrease the chances of current leakage and thereby improve the quality of power supplied to the equipment. In essence, isolation transformers increase the durability of the equipment.

Harmonics Correction

Many industrial machinery incorporate electronic motors that cause harmonic voltage distortions. Such harmonic variations result in malfunctioning of the equipment. Isolation transformers are the best solutions for harmonics correction.

Avoid Earthing Failures

Isolation transformers are highly beneficial because they cut out the conductive connection between the earth and the secondary end and avoid earthing failures.


In order to protect circuits, equipment and people from shocks and short circuits and also make accurate measurements, electrical isolation is required. It is also called galvanic isolation as there is no direct conduction path or physical connection for current to flow. 

Isolation transformers provide electrical isolation. They often include special insulation between the primary and secondary coils and are specified to withstand high voltage between windings. 

Isolation transformers have additional features to reduce noise – common-mode, transverse mode, and electromagnetic. Otherwise, power line or transient voltage noise can be coupled through the capacitance and resistive paths of the coils.

Isolation transformers block DC signals as well as interference caused by ground loops. For sensitive equipment (computers or measuring instruments), they include electrostatic shields to reduce capacitance between the windings.

Using an isolation transformer is not an assurance of safety. At the end of the day, the isolated circuit is a live circuit. When using an isolation transformer, whether powering the unit under test, an oscilloscope or other equipment, you must still follow several safety measures. Know the ground(s) in use, and check voltages and current in your work area and your circuit.