UFC 3-560-01
6 December 2006
Including change 1, 7 December 2006
9-5.1.4.3.5 While the transformer is deenergized, the worker must visually inspect for
obvious symptoms of trouble such as a smoked or burned case, a damaged bushing, or
a damaged fuseholder.
9-5.2
Current Transformers (CT).
WARNING
The most serious hazard associated with the maintenance of CTs occurs
when the secondary side is opened while the primary side is energized.
This causes a very high voltage to develop in the secondary winding,
which both stresses the insulation and presents an extreme personnel
hazard. The secondary circuit of a current transformer must never be
opened while the primary side is energized; however, the secondary leads
can be shorted together without damage to the transformer.
9-5.2.1 Before opening the secondary circuits of any energized current transformer,
the secondary leads must be shorted together and grounded. The location of the short
and ground is preferably located at the transformer secondary terminals, but can be at
any point between the current transformer and the location at which the secondary
circuit is to be opened.
9-5.2.2 Current transformer cases and secondary circuits must be grounded before
energizing any current transformer.
9-6
POWER TRANSFORMERS AND REGULATORS.
9-6.1
Transformers (Power and Distribution).
9-6.1.1 Consider all transformers energized and at full voltage, unless they are
disconnected from primary and secondary wires or disconnected from the primary wires
and all phases shorted together and grounded. The secondary neutral normally is
sufficient as a ground, provided that there is a grounding conductor interconnected with
the common neutral, the transformer case, and a ground electrode. Always check
continuity of the ground connection.
WARNING
Under no conditions should transformer covers or handhole plates be
removed, nor should any work be done on the inside of transformers until
the following instructions have been completed.
9-6.1.2 When transformers are installed or replaced, the secondary terminals will be
checked for correct voltage and for phase rotation (if applicable).
9-9
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