Overload
An overload occurs when an otherwise sound circuit carries more than its intended rating because of the loads connected to it. Several high-power appliances on one extension lead can exceed its rating even without a . Overload is a kind of , and can cause overheating. An alone does not provide overload protection; that is a different protective function.
Where Overload fits in the learning path
The Installation section covers these units:
- Wiring Systems & Enclosures
- Cable Selection & Circuit Design
- Earthing, Bonding & Consumer Units
Curriculum mapping: C&G 2365 Units 203/204/305.
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- Cable SizingInstallation
- Consumer UnitsInstallation
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- Cable Selection — quiz previewPlus · Installation
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Any current above the value a circuit is designed to carry. It comes in two flavours with different time scales: overload, where a healthy circuit is simply asked for too much for too long, and fault current, where a short circuit drives an enormous current that must be broken in milliseconds. Protective devices are chosen to handle both.
Overcurrent
Read the Overcurrent entryCompare related terms
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Overcurrent
Any current above the value a circuit is designed to carry. It comes in two flavours with different time scales: overload, where a healthy circuit is simply asked for too much for too long, and fault current, where a short circuit drives an enormous current that must be broken in milliseconds. Protective devices are chosen to handle both.
Read the Overcurrent entryCurrent-carrying capacity — Iz
The current a cable can carry continuously in its installed conditions without its insulation exceeding the temperature it was designed for. Tabulated values assume reference conditions; the real, installed capacity is what remains after correction factors for temperature, grouping and insulation have taken their share.
Read the Current-carrying capacity entryMCB — Miniature Circuit Breaker
An automatic switch that turns a circuit off when too much current flows, whether a slow overload or a sudden short circuit. It has replaced the rewirable fuse in modern boards. Each one is chosen by its current rating, such as 6 A for lights or 32 A for sockets, and by its type: B for most home circuits, C or D where equipment draws a big surge as it starts.
Read the MCB entryRCD — Residual Current Device
A safety switch that compares the current going out on the line conductor with the current coming back on the neutral. If they differ, current is leaking somewhere it should not, possibly through a person, and the RCD cuts the supply in a fraction of a second. Most socket circuits in UK homes need RCD protection, usually rated at 30 mA.
Read the RCD entryShort circuit
A short circuit is an unintended connection of very low impedance between points that should have a voltage difference, such as line and neutral. It bypasses the intended load and can allow a large current to flow, limited by the supply and circuit impedance. It differs from an overload caused by too many loads. PSCC describes the current that could flow in such a fault, rather than a current flowing in normal use.
Read the Short circuit entryA definition is a start. Using it in a real question is where it sticks.