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Causes current to flow through a circuit
U = voltage, measured in Volts (V)
Is the movement of free electrons
I = current, measured in Amperes (A)
Is the opposition to the movement of free electrons (current)
R = resistance, measured in Ohms (Ω)
Are materials through which electric current can flow freely, examples: gold, silver, copper, aluminum
Are materials through which electric current can not flow freely, examples: PVC, rubber, plastic, glass
An electrical circuit is a closed, continuous, and unbroken loop of conductive material that allows electric current to flow from a power source (like a battery or generator) through components (such as loads like light bulbs, resistors, or motors) and back to the source.
Current flowing through a circuit is directly proportional to the voltage across that circuit, and inversely proportional to the resistance of that circuit
I = U / R
I = Current U = Voltage R = Resistance
Alternatively the formula can be transposed as U = I * R
The cable must be suitable for the load that we want to power. The current carrying capacity of a cable varies with its construction & installation method.
According to Irish Standards: I.S. 10101 Table 52B.1 for a PVC (Thermoplastic) insulated, 2 core, current carrying conductors (Line & Neutral) in a conduit on a wooden wall. We must then use Table 52B.2 Column 5
| Cross Sectional Area (CSA) mm² | Maximum current-carrying capacities in amps |
|---|---|
| 1.5 | 16.5 |
| 2.5 | 23 |
| 4 | 30 |
| 6 | 38 |
| 10 | 52 |
| 16 | 69 |
| 25 | 90 |
| 35 | 111 |
To figure out how many amps a device will use, we can calculate this with the Electric Power Law:
P = U * I
P = power (watts, W) U = voltage (volts, V) I = current (amperes, A)
Most electrical appliances will have a rated power consumption on the box, manual or device itself.
Say for example we have an electric blanket rated at 140W:
140W = 230V * I
I = 140W / 230V = 0.61 Amps
Once we have a cable installed, we must protect it from an Overload / Over-Current event (plugging in too many devices or a dead short by driving a nail through the live conductors) otherwise the cable could over-heat catching on fire, burning down a house.
The design current must be less than The MCB's rated current which must be less than The cable's current carrying capacity.
A Fuse opens the circuit in which it is placed by breaking the current when the current exceeds a given value for a sufficient time.
An MCB can trip in two ways:
Thermal trip from a bi-metallic strip during an overload, caused by a gradual temperature rise due to increased current over time.
Magnetic trip from a solenoid during a high over-current, where a large current produces an instantaneous tripping force.
To protect a circuit from leakage current, which is current flowing through an unintended path back to earth. If a person becomes part of a live circuit, 50mA is enough to kill, therefore most RCD's are set to trip at 30mA.
We can additionally protect our sensitive electronic devices in our homes like TV's and medical equipment from High Voltage spikes which may occur on the incoming electricity connection.
This can occur from lighting strikes, transformers failing on the grid or Industrial factories switching large motors in your area.
SPD's should be installed as close as possible to the origin of an installation, with the shortest possible cable runs used, The max cable run allowed is 0.5m (The idea is to have the SPD absorb the voltage spike before it reaches into your home and damage your equipment)
An SPD needs to be protected against Over-Current, This protection may be internal to the SPD or required externally, It is your responsibility to check this with the Manufacturer's instructions.
MCB: Miniature Circuit Breaker, designed to protect low-current circuits (Domestic)
MCCB: Molded Case Circuit Breaker, designed to handle higher levels of current (Industrial)
RCD: Residual Current Device, disconnects the power when it detects current leaking to earth
RCBO: Residual Current Breaker Over-current, Combines functions of an RCD & MCB
AFCI: Arc Fault Circuit Interrupters, detects dangerous electrical arcing and disconnects the circuit to prevent fires.
Type B: Trips at 3-5 times rated current
Type C: Trips at 5-10 times rated current
Type D: Trips at 10-20 times rated current
Type AC: Designed for AC currents (old, no longer recommended)
Type A: Designed for AC + pulsating DC currents
Type B: Designed for AC + pulsating DC currents + PV systems + EV chargers
Type F: Designed for AC + pulsating DC currents + mixed frequency VFD (e.g. heat pumps, air conditioning)
Type 1 SPD: Protects against lightning strikes entering the installation.
Type 2 SPD: Protects against switching surges within the installation.
Type 3 SPD: Protects sensitive equipment close to the load.
resistance testing + disconnection times
<2MΩ insulation resistance is problematic.
Mains Electricity in Ireland:
230V AC 50Hz
LV: Low Voltage
Voltages exceeding 50 VAC or 120 VDC, but not exceeding 1,000 VAC or 1,500 VDC.
ELV / SELV: Safe Extra Low Voltage
Voltages not exceeding 50 VAC or 120 VDC between conductors at any point of a circuit.
Isolating transformer:
The input winding of which is electrically separated from the output winding by insulation.
Safety transformer:
The input winding of which is electrically separated from the output winding by insulation, and which is designed to supply SELV circuits.
Line conductor:
Conductor which is energized in normal operation and capable of contributing to the transmission or distribution of electric energy, but which is not a neutral.
Neutral conductor:
Conductor electrically connected to the neutral point and capable of contributing to the distribution of electric energy.
PEN:
Conductor combining the functions of both a Protective Earthing conductor and a Neutral conductor.
Leakage current / Earth current:
Electric current in an unwanted conductive path under normally operating conditions.
MOD:
Main Over-Current Device.
The 1st coloured band = The value of the 1st digit
The 2nd coloured band = The value of the 2nd digit
The 3rd coloured band = The number of 0 digits
| Better | Black | 0 |
| Be | Brown | 1 |
| Right | Red | 2 |
| Or | Orange | 3 |
| Your | Yellow | 4 |
| Great | Green | 5 |
| Big | Blue | 6 |
| adVenture | Violet | 7 |
| Goes | Grey | 8 |
| Wrong | White | 9 |
The 4th coloured band = The % tolerance
| Gold | +/- 5% |
| Silver | +/- 10% |
| No band | +/- 20% |