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S1-Q29.) Which type of transformers must always be shunted prior to performing maintenance operations on
them?

a.) Potential transformers
While it is good idea to shunt all transformers it is very unlikely that a potential transformer would
have stored energy. Once energy is removed from a potential transformer, there is no residual flux
that could collapse and cause current to flow.
b.) Current transformers
Correct. When opening the secondary of a CT, the voltage level induced from the primary may
be exceptionally high. The primary current continues to flow causing a large arc on the
secondary if opened. This could also lead to serious shock and/or death. Shunting the
secondary will not harm the CT since the secondary current is always very low and is a function
of the number of turns (usually one or two).
c.) Autotransformers
Voltage must be removed from the primary and secondary to do maintenance since the primary is part
of the secondary in autotransformers. Therefore, there is no energy that could cause damage or injury.
d.) Isolation transformers
Shunting an isolation transformer could cause damage as the turns ratio is usually 1:1. removing
power from the primary will remove all power and/or residual flux to collapse. Safety will then not
be an issue.

S1-Q30.) Fuses should NEVER be installed

a.) In series with the load
Fuses must always be placed in series with the object they are supposed to protect.
b.) *In series with the neutral
Correct. If the fuse were to open the “hot” side would still be energized causing a possible
short circuit condition if an operator touched the device. This may result in DEATH.
c.) So they will protect the circuit before other safety devices
Fuses are the only electrical device designed to fail. Having them fail first is usually desirable.
d.) So they can be easily removed and replaced after failure
Quick replacement reduces down-time.

S1-Q31.) Which of the following is not used to limit current in a circuit?

a.) Fuse
Low Cost device designed to fail in order to protect equipment.
b.) Ratchet, Pivot, and Pawl
Mechanism used in overload relays for motors. When the eutectic alloy (solder-pot) receives
sufficient heat from the load’s current, the ratchet begins to rotate and the spring loaded pawl moves
the Pivot Arm opening the relay contacts and shutting down the motor. Once the eutectic allow cools,
the device may be reset without replacing any parts.
c.) *Silicon Controlled Rectifier (SCR)
Correct. This is a device used control the amount of voltage used by a device by only turning on
at specified angles of the sine-wave. It has nothing to do with protecting equipment.
d.) Magnetic Circuit Breaker
As current increases past a set level, the magnetic field generated by that current exceeds the rating of
the breaker and causes contacts to be pulled apart. Once the fault has been cleared, the breaker may
be reset without replacing any components.

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