The term demarcation means the setting or marking of boundaries or limits. Demarcation point is the service point where the electrical-utility power transmission/distribution grid with installation governed by the NESC (National Electrical Safety Code) stops, and the electrical power distribution system for a building or other structure (premise electrical-power distribution system) with installation governed by the NEC begins.
Dielectric / Dielectric Strength.
A dielectric is an insulator. Dielectric strength relates to the maximum voltage that a given insulation can withstand without breaking down.
Difference of Potential / Potential Difference.
The voltage created between two points in an electrical system separated by an open circuit or other impedance when supply power is applied. The voltage measured across a circuit or circuit component is often referred to as the potential difference as well.
Double-Insulated / Ungrounded Tool.
Any of several ungrounded electrical tools that are constructed so that the case, normally made of a nonconductive material, contains a second type of insulation from electrical energy.
An insulating material between the plates inside of a capacitor.