1st of all, there are much better ways to test those windings, not sure where you found that testing procedure. PI, DAR, and MCE testing is more common.
2nd, to answer your question:
1910.269(l)(1)(i) Except as provided in paragraph (l)(1)(ii) of this section, at least two employees shall be present while the following types of work are being performed:
(l)(1)(i)(A) Installation, removal, or repair of lines that are energized at more than 600 volts,
(l)(1)(i)(B) Installation, removal, or repair of deenergized lines if an employee is exposed to contact with other parts energized at more than 600 volts,
(l)(1)(i)(C) Installation, removal, or repair of equipment, such as transformers, capacitors, and regulators, if an employee is exposed to contact with parts energized at more than 600 volts,
(l)(1)(i)(D) Work involving the use of mechanical equipment, other than insulated aerial lifts, near parts energized at more than 600 volts, and
(l)(1)(i)(E) Other work that exposes an employee to electrical hazards greater than or equal to those posed by operations that are specifically listed in paragraphs (l)(1)(i)(A) through (l)(1)(i)(D) of this section.