Final answer:
In TTL circuits, an isolation transformer is used to electrically isolate the transmitter from the receiver, providing a safety layer by adding high resistance to prevent a complete circuit.
Step-by-step explanation:
The special electrical device used in TTL circuits to electrically isolate the transmitter from the receiver is an isolation transformer. The isolation transformer provides a large resistance between the original voltage source and the device being operated, which helps prevent a complete circuit between the two, even if there is physical contact with one of the transformer's output wires. By isolating the appliance from the original voltage source, the isolation transformer ensures that the person touching the output wire is not part of a complete circuit, significantly reducing the risk of electrical shock.