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Subsequently, one may also ask, does DC need a ground?
Circuits powered by batteries do not have an earth ground. Batteries do not have have a connection to the physical earth. So most DC-powered circuits, especially by batteries, have a floating ground, not an earth. So if you have a 5-volt voltage source, from ground (0 volts), it is 5 volts.
In respect to this, why do circuits need a ground?
Electrical power distribution systems are often connected to ground to limit the voltage that can appear on distribution circuits. A distribution system insulated from ground may attain a high potential due to transient voltages caused by arcing, static electricity, or accidental contact with higher potential circuits.
(1) All 3-wire DC systems must have their neutral conductor grounded. (3) AC circuits of less than 50 volts must be grounded if they are installed as overhead conductors outside of buildings or if they are supplied by transformers and the transformer primary supply system is ungrounded or exceeds 150 volts to ground.