Last month, we dealt with the construction of a low-voltage transformer (Photo A).1 This tool can supply low voltage AC excitation to unknown iron-core power transformers to help identify and characterize them. The low-voltage approach is intended to reduce the likeliness and severity of electric shock. As mentioned last month, safety and liability are your own responsibilities. You are the responsible party, no one else. This concluding article will offer an old safety procedure to reduce risk, and a few examples of how to use this tool.
Continuity Testers
I advocate using continuity testers. These simple devices can rapidly discover shorts and open circuits, and you do not have to read any numbers. Simple continuity tests can also help reveal unsafe or defective transformers. Healthy transformers should exhibit a continuous primary and a continuous secondary; and should not show continuity from the primary to the laminations, from primary to secondary, or from secondary to the laminations, in most instances. There are some exceptions: The secondary of some high-voltage (HV) transformers are connected to the laminations. Many neon sign transformers and microwave oven transformers exhibit continuity from secondary to laminations.
Ohmmeters
An ohmmeter can also help identify unknown transformers. In general, manufacturers use smaller diameter
