plumbing scince

Question 1

Voltage = V

Answer 1

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).

Question 2

Current = I

Answer 2

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).

Question 3

Resistance = R

Answer 3

The ohm is the unit of resistance, which opposes the flow
ofcurrent.

Question 4

Watts = W

Answer 4

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).

Question 5

Joules = J

Answer 5

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.

Question 6

If an appliance needs 3kW in a domestic property, what

is the fuse size?

Answer 6

12.5 amp.

Question 7

In a domestic property, an appliance has a fuse size of

3 amp. What is the maximum power rating of the

Question 8

An appliance has a 5 amp fuse and needs 1.2kW of

power. What is the voltage required?

Answer 8

240v.

Question 9

What would be the resistance of a domestic appliance

Answer 9

the fuse size was 3 amp?80 ohms.

Question 10

DC = direct current = batteries (chemically)

Answer 10

Dissimilar metals in a dilute acid solution

Cathode eats away at the anode

Question 11

In a domestic property:

Answer 11

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.

Question 12

Dedham: Electrocuted builder’s death was an accident

Answer 12

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.

Question 13

Lighting circuit:
Radial circuit

Answer 13

1.5mm twin and earth

6 amp circuit protection

One circuit upstairs and one

Question 14

Ring circuit

Answer 14

Sockets

2.5mm twin and earth

32 amp circuit protection (consumer unit)

13 amp appliance protection (plug)

Question 15

Minature circuit breaker (MCB)

protection of circuits

Answer 15

Lighting
6 amp

Immersion
16 amp

Water heater
16 amp

Ring final
32 amp

Cooker
32A-45A (typically) amp

Question 16

As plumbers, we are not allowed to interfere with either
the ring final or lighting circuit.

Answer 16

Only a qualified electrician – competent person

We can attach an appliance from a fused spur.

Question 17

Consumer unit

Answer 17

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.

Question 18

Consumer unit

Answer 18

If an MCB needs replacing, the main isolator in the
consumer unit would have to be isolated while an
electrician replaced the item.

Question 19

Mains supply

Suppliers fuse

Meter

Consumer unit

Feeds the circuits

Answer 19

Earth bar

Up to the meter is the
responsibility of the supplier.

From the meter tails
onward is the responsibility
of homeowner.

Question 20

Central heating S plan

Answer 20

Wire in from switched fused spur:

• Programmer
• Cylinder thermostat
• Room thermostat
• Boiler
• Pump
• 2 x two port valves

Question 21

Central heating Y plan

Answer 21

Wire in from switched fused spur:

• Programmer
• Cylinder thermostat
• Room thermostat
• Boiler
• Pump
• 1 x three port valve

Question 22

Domestic electrics

Answer 22

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.

Question 23

Miniature circuit breakers (MCB):

Answer 23

Found in the consumer unit and protect one appliance
or circuit

Trip out if an overload is detected.

Question 24

Residual circuit breakers (RCD):

Answer 24

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.

Question 25

Fuses and MCBs are there to protect the circuit and
appliance. If an appliance or circuit is overloaded, the
insulation in the cable is the first item to get damaged
and possibly burnt.

Answer 25

The fuse inside a fused spur will protect the cable and
appliance.

Any visual faults need to be reported to the homeowner
or your supervisor for them to make a decision.

Question 26

Domestic electrics

Answer 26

Cartridge fuses are the older type of circuit protection
and are re-wireable

Plug tops have cartridge fuses inside.

Question 27

All circuits and appliances must be protected by the

Answer 27

use of a fuse or MCB. Modern regulations also require
the use of an RCD

Every circuit and appliance must also have a means of
isolation

Permanent de-commissioning is done at consumer unit

Temporary de-commissioning can be done at appliance.