plumbing scince Flashcards
Voltage = V
The unit for electromotive force (emf). The higher the
voltage the greater the force is to cause electrons to flow
along the conductor (eg 240v for domestic).
Current = I
The ampere is the unit of current, and can be defined as
the unit of quantity or volume passing down a conductor.
(3 amp fuse).
Resistance = R
The ohm is the unit of resistance, which opposes the flow
ofcurrent.
Watts = W
It is the unit of power for an appliance. Power is used to
make an appliance work; as some power is absorbed, an
appliance is never 100% efficient (e.g 3kW immersionheater).
Joules = J
The unit of electrical energy. As this is so small, it is not
generally used. Today it would be measured in the
kilowatt hour, which is how electricity bills are measured.
If an appliance needs 3kW in a domestic property, what
is the fuse size?
12.5 amp.
In a domestic property, an appliance has a fuse size of
3 amp. What is the maximum power rating of the
An appliance has a 5 amp fuse and needs 1.2kW of
power. What is the voltage required?
240v.
What would be the resistance of a domestic appliance
the fuse size was 3 amp?80 ohms.
DC = direct current = batteries (chemically)
Dissimilar metals in a dilute acid solution
Cathode eats away at the anode
In a domestic property:
Sockets are 230v single phase AC
Use a step-down transformer for 110v single phase AC
May also use battery operated tools, which will be 24v,
18v or 12v DC.
Dedham: Electrocuted builder’s death was an accident
Father-of-three, Paul Hamlyn, 44, of Chase Road West in Great
Bromley, was killed when he touched a live cable at a house in
Forge Street, Dedham.
“We had the toilet macerator changed about six or eight weeks
ago and the plumber had put it on a normal plug and not
re-wired it back into the fuse box,” the customer said.
“Paul said he knew someone who could do any electrical work
if it needed doing – I can’t think why he moved the wire. I think
he was reaching for his tool box.”
A post-mortem at Colchester General Hospital concluded that
the victim had died of electrocution.
Lighting circuit:
Radial circuit
1.5mm twin and earth
6 amp circuit protection
One circuit upstairs and one
Ring circuit
Sockets
2.5mm twin and earth
32 amp circuit protection (consumer unit)
13 amp appliance protection (plug)
Minature circuit breaker (MCB)
protection of circuits
Lighting
6 amp
Immersion
16 amp
Water heater
16 amp
Ring final
32 amp
Cooker
32A-45A (typically) amp
As plumbers, we are not allowed to interfere with either
the ring final or lighting circuit.
Only a qualified electrician – competent person
We can attach an appliance from a fused spur.
Consumer unit
Found where the electrics enter the property
Contains all MCBs, residual current device, RCDs and main
isolator
Where the single source is divided into multiple circuits.
Consumer unit
If an MCB needs replacing, the main isolator in the
consumer unit would have to be isolated while an
electrician replaced the item.
Mains supply
Suppliers fuse
Meter
Consumer unit
Feeds the circuits
Earth bar
Up to the meter is the
responsibility of the supplier.
From the meter tails
onward is the responsibility
of homeowner.
Central heating S plan
Wire in from switched fused spur:
- Programmer
- Cylinder thermostat
- Room thermostat
- Boiler
- Pump
- 2 x two port valves
Central heating Y plan
Wire in from switched fused spur:
- Programmer
- Cylinder thermostat
- Room thermostat
- Boiler
- Pump
- 1 x three port valve
Domestic electrics
Correct earthing is very important, as the majority of
electric shocks and electrocutions are due to incorrect
earths or earthing faults
Any problems should always be reported to the
customer.
Miniature circuit breakers (MCB):
Found in the consumer unit and protect one appliance
or circuit
Trip out if an overload is detected.
Residual circuit breakers (RCD):
Found in modern consumer units
Trip out if there is an earth fault (test and re-set
switch)
Plug-in RCDs should be used with 230v tools.
