Page 198 - The City and Guilds Textbook: Plumbing Book 1 for the Level 3 Apprenticeship (9189), Level 2 Technical Certificate (8202) and Level 2 Diploma (6035)

The City & Guilds Textbook: Plumbing Book 1

These relationships between current, voltage and resistance are the theory
behind Ohm’s law, which will be looked at in detail later in this section.

IMPROVE YOUR MATHS

Resistance can be calculated by:
Voltage (V) ÷ Current (I)

Amperage

In the UK, voltage is supplied at 230 V, but different appliances need different
amounts of electricity in order to work effectively. The rate at which electricity flows
through an appliance is known, in electrical units, as amperage, often shortened to
amps. If we consider that water at a certain pressure with a certain size pipe will
deliver a set amount of water, if we increase the pipe size, then the pressure stays
the same but the flow rate increases. In electrical terms, if voltage is the pressure
then amps is the flow rate; the bigger the cable, the bigger the flow rate or amperage.

The ampere, symbol I, is the SI unit of electric current, and is defined in terms of
the coulomb: 1 ampere is the amount of electric current (flow rate of electricity)
carried by a charge of 1 coulomb flowing for 1 second.

IMPROVE YOUR MATHS
Amps can be calculated by:

Voltage (V) ÷ Resistance (R)

Power
The rate at which electric energy is converted to other forms of energy, such as
heat, light or mechanical, is called power (P) and is equal to the sum of the current
and the voltage. An electrical shower that is rated at, say, 8 kW simply means that
the electrical power of 8 kW is converted into heat to heat the water. Electrical
power is, therefore, the rate at which electricity is produced or consumed, and can
be defined as the amount of electric current flowing due to the voltage.

IMPROVE YOUR MATHS
Electrical power is measured in watts (W). The formula is:

Current (I) × Voltage (V) = Power (W)

The types of electrical current
There are two types of electrical current. These are:

1 direct current
2 alternating current.

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