MIL-HDBK-1025/10
transformers are installed or replaced, their secondaries should be checked for voltage and phase
rotation when necessary. When distribution transformers are installed and before they are
energized, the ground connections should be made to the case, secondary neutral, and then to the
primary neutral when used, in the order named.
7.12.4.1 Aerial Energized Work. Except for testing, replacement of fuses, and
switching, work on energized pole-mounted transformers and lines is prohibited.
7.12.4.2 Aerial Installation. To meet these requirements, engineering guidance may be
necessary.
a. All frames and tackles used in erecting pole-type transformers should be carefully
inspected each time before use. Defects should be repaired before the frames and tackles are
used.
b. Wherever possible, junction poles, subsidiary poles, and streetlighting poles should not
be used as transformer poles. When it is necessary to install transformers on junction, subsidiary,
or streetlighting poles, take care to maintain proper climbing space and to avoid crowding of
wires and equipment.
c. Transformers should be installed only on poles strong enough to carry their weight.
Transformer poles should be straight and, where necessary, guyed to prevent leaning or raking of
the pole after the transformer is hung.
d. When transformers are raised or lowered, all crew members should stand clear and
traffic should be detoured if necessary. In congested traffic, the pole space should be roped off.
Personnel on the pole should place themselves on the opposite side from that on which the
transformer is being raised or lowered. Pole steps and other obstructions in the path of
ascent/descent of large transformers should be removed.
e. When transformers are installed, the pole climbing space should be carefully maintained
so that it will not be necessary for climbing workers to come too close to the transformer case.
7.12.4.3 Aerial Connection. Pole-type transformers should not be installed until they are
supplied with a sufficient amount of good quality oil.
a. When a three-phase bank of pole-type transformers is replaced, the new transformers
should be carefully checked for phase rotation before service is restored, so that the new service
connections will be the same as before the change. If incorrect phase rotation results, any
connected motorized equipment will be dangerous as it will revolve in the wrong direction.
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