What is the lowest transformer tap?

The universal answer to this question is the number 1 tap. The deeper question is what does this represent? Transformers vary in design so the number 1 tap can also vary by design. What does not vary is that the lowest tap connects the primary to the maximum number of turns in the transformer. This will produce the lowest voltage available from the transformer. This low voltage will in turn drive lower currents and welding power. All other tap settings will produce more voltage and power being delivered to the resistance welder.

 Tap Rating of 100 KVA Transformer

This table represents a 100 KVA AC press welder transformer. It exhibits two methods of wiring the taps on the same transformer. In this case there is a series/parallel tap switch. The upper range is wired in parallel. The lower range is wired in series and produces the lowest power.
There are many transformer designs and options to design the output voltages. Therefor the actual tap outputs will vary but tap 1 will always be the lowest voltage/power option available.

Reference: RWMA Manual Chapter 19

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