basics of electrical

potential difference

Charge moving in an electric circuit gives rise to a current, Naturally, it must take some work, or energy, for the charge to move between two points in a circuit, say, from point a to point b. The total work per unit charge associated with the motion of charge between two points is called voltage. …

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kirchhoff’s current law

Kirchhoff’s laws govern the conservation of charge and energy in electrical circuits. Kirchhoff’s Laws The junction rule The closed loop rule At any node (junction) in an electrical circuit, the sum of currents flowing into that node is equal to the sum of currents flowing out of that node, or: The algebraic sum of currents …

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elementary charge

The word electricity originated about 600 B.C.; it comes from elektron, which was the ancient Greek word for amber. The true nature of electricity was not understood until much later. the atomic structure of matter, consisting of a nucleus—neutrons and protons—surrounded by electrons. The fundamental electric quantity is charge, and the smallest amount of charge …

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electrical network elements

An electrical network is a collection of elements through which current flows. The following definitions introduce some important elements of a network. Branch A branch is any portion of a circuit with two terminals connected to it. A branch may consist of one or more circuit elements Node A node is the junction of two …

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ideal current source

An ideal current source is a device that can generate a prescribed current independent of the circuit to which it is connected. To do so, it must be able to generate an arbitrary voltage across its terminals.

Ideal Voltage Sources

An ideal voltage sources are an electric device that generates a prescribed voltage at its terminals. The ability of an ideal voltage source to generate its output voltage is not affected by the current it must supply to the other circuit elements. Note that the output voltage of an ideal source can be a function …

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what is residual current

No commentary on protective devices would be complete without reference to residual current devices. The IEE Regulations specify that, provided the required disconnection times can be met for circuits and all bonding is in place, fuses and/or CBs will provide the necessary protection against electric shock. RCDs are only required • when disconnection times cannot …

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earth fault loop impedance

circuit protection should operate in the event of a fault to earth. The speed of operation of the protective device is of extreme importance and will depend on the impedance of the earth fault loop path. • the circuit protective conductor (CPC)• the consumer’s earthling terminal and earthing conductor• the return path, either metallic or …

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electric shock

This is the passage of current through the body of such magnitude as to have significant harmful effects. below Figure illustrates the generally accepted effects of current passing through the human body. How, then, are we at risk of electric shock and how do we protect against it? 1 mA–2 mA Barely perceptible, no harmful …

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