Electrical Systems Flashcards
How do we measure electrical pressure?
The “pressure” in an electrical system is measured in Volts, and normally annotated as “V”.
How do we measure the quantity of electricity drawn through a circuit?
Current is drawn through a circuit, measured in Amps and represented by the letter I for intensity.
Describe a direct current.
In a DC circuit, the current flows in one direction, often from the positive terminal of a battery, through the load and back to the battery’s negative terminal.
Stays constant
Can be positive or negative
Many end devices use DC power from batteries or a transformer.
Describe alternating current.
In an AC circuit, the power changes (usually 50-60 times a second) from positive to negative, following a sine wave pattern.
Both “positive” and “negative” terminals are effectively live.
What is the risk of short circuits?
Electricity will follow all available pathways to return to its source, or Earth as an alternative.
If an additional pathway is unintentionally created, electricity may flow in an unexpected area putting users at risk, as well as damage equipment.
What is power?
Power is a measurement of work done, and is normally measured in watts (W).
1 amp flowing though 1 ohm equals 1 watt.
What do we mean by V=I*R?
Voltage equals Current times Resistance.
Current therefore equals Voltage divided by Resistance.
What is the relationship between power, current and voltage?
Power equals current times voltage.
E.g. the power of a light bulb (in watts) is the current (0.25A) times the Voltage (240V).
Therefore, the power of a lightbulb drawing 0.25A is 60W.
Current is power divided by voltage, so 60W divided by 240V is 0.25, so to calculate the fuse required (current), divide the power (in W) of the load by the voltage.
What is the difference in readings between a series circuit and a parallel circuit, each with three loads or resistors?
In a series circuit the voltage is divided between the three resistors, and the current stays the same, whereas in the parallel circuit the voltage stays the same and the current is split between the three loads.
What useful feature does grounding provide?
Grounding an installation provides a quick route to ground for any electricity, thereby reducing exposure to users. By providing an escape route minimises the danger of fire or electrocution.
How is power distributed within a building?
Power from the central power input is normally fed to separate panel boards or subpanels looking after specific parts of the premises. Circuit breakers are often installed as an additional safety measure.
What is the maximum you could ever load an electrical circuit?
Never go beyond 80 per cent of the rated electrical system capacity.
