Laminated Core design transformers also referred to as Auto transformers are the pick of choice for most applications. They are suited to applications where the voltage conversion ratio is less than 3:1.
8ZED Step Down Transformers are Laminated Core design and shielded between primary and secondary lamination’s to reduce EMI or electromagnetic interference. Thermal protection cut out, is built into the winding to protect against overheating. Laminated Core Step Down Transformers are considerably cheaper, lighter, smaller, and more efficient than an Isolated Toroidal Transformer of the same power rating.
Single winding auto transformers are also commonly found in large three-phase electric power distribution networks, to interconnect sub-transmission stations. They are the most commonly deployed because they are the most efficient method of voltage conversion, eg typically 66 KVA to 33 KVA. These Auto transformers are not fully shielded so they emit a low register hum, which you can sometimes here around sub stations. The main advantages when used in sub stations is the auto transformer is smaller, lighter, and cheaper than typical dual-winding transformers. Other advantages of Auto transformers include lower leakage reactance, lower load losses, lower excitation current, and increased KVA rating.
Where equipment is being used by multiple end users, particularly medical or quasi medical equipment, isolation transformers are preferred but not essential. The exception is certain environments e.g. hospitals, surgeries etc. but with special leakage protection circuits. The electrical isolation of dual windings means there is no current leakage, particularly important in research and medical applications. 8ZED Toroidal transformers are designed to virtually eliminate the external magnetic field noise interference around the transformer, important when the volume on amplifiers are cranked up and voltage conversion ratios rise well above 3:1. Toroidal Transformers have doughnut shaped twin windings, which are used to save space. However, the isolated transformers remain much larger than the more commonly used Laminated Core Step Down Transformers for a given power rating. The Toroidal windings require more complex and slower production equipment and therefore cost a lot more to make.
Normal earth leakage equipment will not work at all with standard isolation transformers and therefore personnel are less protected and in public/semi public circumstances this is a real issue, far beyond equipment protection, especially in wet/moist environments or with equipment that has contact with people.
Auto transformers are no more likely to fail than similarly constructed isolation transformers.