Toroidal isolation transformers use the same operating principle as other transformers. A primary winding surrounding an iron core generates an electrical field in the core. This electrical field induces an electrical field in a secondary winding resulting in a voltage across the winding and an electrical current.

The turn winding ratio between the primary winding and the secondary winding determines the voltage ratio between the primary circuit and the secondary circuit. The large transformers you see on utility poles have different numbers of turns in the primary and secondary windings. These transformers are called step up and step down transformers because their purpose is to increase or decrease, respectively, the voltage on each side of the transformer.

By contrast, a toroidal isolation transformer has the same number of turns in the primary and secondary windings. As a result, the voltage in the secondary circuit is the same as the voltage in the primary circuit.

Why would a circuit include a transformer that has the same voltage on each side? Because the current in the secondary circuit is induced, it is physically isolated from the current in the primary circuit. In other words, there is no conductor that connects the primary circuit to the secondary circuit.

This has important effects:

  • Current cannot flow directly from the primary circuit to the secondary circuit.
  • The primary circuit is not grounded by the secondary circuit.

Those without experience in electrical engineering may ask, what does this mean? In effect, this means that when the second circuit is short circuited or grounded, a surge of current does not flow from the voltage source to the ground. As a consequence, anything in the way of the current, whether it be a human body or sensitive electronic devices, will not be electrocuted or fried.

Here are two industries that make use of isolation transformers:

Medical Isolation Transformers

The U.S. had over 6,200 hospitals in 2017. These hospitals had over 36 million admissions and employed over 7 million doctors, nurses, and staff that year. With this number of patients and medical personnel who come into contact with electrical medical equipment, electrocution is bound to happen at least occasionally.

Toroidal isolation transformers are used to isolate patients and staff from voltage sources, such as regular AC power flowing through the electrical lines and sockets of medical clinics, hospitals, and doctor’s offices. The reason for this should be obvious. Whether accidental or due to misuse, patients who are in physical contact with electrical medical equipment are at risk of electrocution.

By introducing a toroidal isolation transformer into the circuit, current cannot run from the voltage source, namely the electrical socket, through the patient to ground. Without this electrical pathway, the risk of electrocution is substantially reduced. Similarly, a sudden voltage surge cannot be passed from the voltage source, through the medical equipment, to the patient if the voltage source is isolated from the patient with custom made toroidal transformers. Thus, both the patient and the medical equipment are protected from electrocution and damage resulting from short circuits caused by damaged wires and liquid spills.

Marine Isolation Transformers

Ship-board isolation transformers are introduced between a shore power connection and the onboard power converter and battery charger. These portable isolation transformers protect both the vessel and anyone onboard by isolating the shore power source from the vessel. These are used whether the vessel is a personal boat or a commercial ship.

The isolation transformer prevents current leaking from the shore power source from electrifying the vessel or the water surrounding the vessel. A phenomenon known as electric shock drowning (ESD) occurs when current leakage from a shore power source electrifies the water around a vessel. Anyone swimming through the electrified water risks electrocution when they are electrically grounded by touching the vessel or sea bottom. A toroidal isolation transformer can prevent current leakage from reaching the water around the vessel.

Similarly, shore power or polarity reversals can electrify the vessel or electrical appliances on the vessel. These electrified surfaces can cause electrocution. The risk of this type of electrocution can be substantially reduced by a marine isolation transformer.

Toroidal isolation transformers serve an important electrical safety role in dangerous environments such as hospitals and marine vessels.