Neutral - The junction point of the legs in a Wye circuit.
Neutral Grounding Resistor - A grounding device, the principal element of which is resistance, which is used to connect the neutral point of the transformer to earth.
Normal Duty - A lightning impulse classifying current category for distribution class arresters defined by ANSI/IEEE C62.11. A normal duty rated arrester has 5000 amperage impulse value crest (refer to heavy duty)
NM - Nonmetallic-sheathed (plastic).
NMC - Solid plastic nonmetallic-sheathing used in wet or corrosive areas, but not underground (see UF).

Ohm - A unit that measures the resistance a conductor has to electricity.
Ohm's Law - Voltage equals resistance multiplied by current.
Overvoltage - A voltage above the normal rated voltage or the maximum operating voltage of a device or circuit. A direct test overvoltage is a voltage above the peak of the line alternating voltage.