6.8.2 Current Transformers. These units provide a method of obtaining a
lower amperage at a low-voltage from a higher-voltage circuit. Current transformer cases
and secondaries should be grounded before energizing any current transformer.
The main risk involved with the maintenance of current
transformers occurs when the secondary side is unintentionally
opened while the primary side is energized. Opening the
secondary side causes a very high voltage to be set up in the
secondary winding, which stresses the insulation and presents a
serious personnel hazard.
220.127.116.11 Circuit Opening. The secondary circuit of a current transformer should
not be opened while the primary side is energized. Before opening the secondary circuits
of any current transformer, the secondary leads should be short-circuited and grounded at
some point between the current transformer and the location at which the secondary
circuit is to be opened.
Power Transformer and Regulator Safety. Power transformers change
voltage levels. Voltage regulators apply needed control for variations in loads whose
effect on line-voltage drop exceeds that which is acceptable. Both require regular
servicing but their protective and circuit disconnecting means are not necessarily similar.
Refer to Section 7 for additional power transformer safety requirements.
6.9.1 Power Transformers. Consider all transformers energized and at full
voltage, unless they are disconnected from primary and secondary wires, or unless they are
disconnected from the primary wires and then short circuited and grounded. The
secondary neutral will be considered a sufficient ground, provided there is a grounding
conductor that is interconnected with the common neutral, the transformer case, and a
ground electrode. Always check continuity of this ground connection. When removing
transformers, the case and neutral grounds should be disconnected last.
Under no conditions should transformer covers or handhole plates
be removed, nor should any work be done on the inside of
transformers until these instructions have been complied with.
a. When transformers are installed or replaced, the secondaries will be checked for
correct voltage and, where applicable, for phase rotation.
b. When transformers are installed, and before they are energized, the ground
connection will first be made to the case and to the neutral when applicable.