**Radial Feed** - One primary bushing per phase.

**Rating** - The rating of an arrester - either
duty cycle or MCOV rating.

**Ratio** - A reference to either the turns ratio
or the voltage ratio of a transformer.

**Reactance** - A component of impedance produced
by either inductance or capacitance in an ac circuit.

**Recloser** - An automatic, high-voltage electric
switch (see "What is a
Recloser?").

**Recovery
Voltage** - The voltage potential established across the open
electrodes of an overcurrent protection device after clearing the
circuit at a current zero; a term used to designate the voltage
impressed by the circuit upon the interrupting device after
interruption of the current at or about the time of a natural
current zero.

**Reduced
Capacity Tap** - Tap that is not designed to deliver the rated
capacity of the transformer.

**Reference
Current (Iref)** - The reference current is the peak value of
the resistive component of a power frequency current high enough
to make the effects of stray capacitance of the arrester
negligible. This current level shall be specified by the
manufacturer.

**Reference
Voltage (Vref)** - The lowest peak value independent of
polarity of power frequency voltage, divided by the square root
of 2, required to produce a resistive component of current equal
to the reference current of the arrester or arrester element. The
reference voltage of a multi-unit arrester is the sum of the
reference voltages of the series units. The voltage level shall
be specified by the manufacturer.

**Resistor**
- Any device of material that limits the flow of current when
voltage is applied.

**Resonance**
- A state in which the capacitance and the inductance values in a
circuit are equal (net reactance is equal to zero) and the only
quantity left is resistance.

**Resonant
Frequency** - Frequency at which the voltage and the current at
the input terminals are in phase. Reactance is equal to zero.

**RMS
Line Current** - The square root of the average of the squares
of all the instantaneous current amplitudes occurring during one
cycle.

**Routine
Tests** - Test made by the manufacturer on every device or
representative samples, or on parts or materials, as required, to
verify that the product meets the design specifications.