Design Study
electric table lamp
J Errington MSc
Metal body table lamp
A frame of machined and cast brass
supports a hemispherical maroon
colored translucent glass shade with
an acid etched surface, and original
Edison screw socket.
Condition
Perfect, rewired with new
reproduction cloth covered flex, fitted
discreetly with an earth connection.
Dimensions
42.5cm high (16.75").
Insulating body table lamp
4" Iris Table Lamp
Made of pottery and hand
painted. The iris design is
carved in low-relief on the
outside. The base is
scalloped so that your
favorite side can face the
front. The total height is 25"
with a 5 x 17 x 11" shade.
Design criteria
• Must meet electrical safety standards
• Must meet fire safety standards
• Stability of shape – how easy to knock
over
• Choice of appropriate materials
Electrical safety regulations
Two categories of protection against electrical
shock
• Class 1: All exposed metalwork that is not
already shielded from live parts by an earthed
screen shall be connected to a protective earth
of low impedance
• Class 2: All live parts of the appliance shall be
protected by two independent layers of
insulation (double insulated)
Class 1
• Insulation between mains and any
accessible part shall withstand a flashover
voltage of 2120V
• The minimum distance between mains
voltage carrying parts and touchable parts
must be 3mm.
• All touchable parts must be properly
earthed.
Class 2
• Insulation between mains and every touchable
part shall withstand a flashover voltage of 4240V
• The minimum distance between mains voltage
carrying parts and touchable parts must be
6mm.
• Double insulated construction should be so
designed that failure of two independent layers
of insulation has to occur before any exposed
metalwork can become connected with a live
conductor.
Practical considerations for design
of electrical appliances
• Keep mains carrying parts as compact as
possible and well away from other parts of the
design
• Only use approved parts for mains carrying parts
of the equipment e.g. cable entry, switch, fuse
holder, lamp holder
• Use only approved colour coded wires
throughout the design.
• Remember mains operated equipment may get
hot so choose materials that will withstand this.
Static and dynamic equilibrium
A structure will be
stable, ie hard to knock
over, if the centre of
gravity has to rise for
this to happen.
Fire safety
• Minimise risk by ensuring only those parts
intended to get hot do so.
• Keep combustible materials away from sources
of heat
• Use protective devices (electrical and thermal
fuses) to disconnect appliance if there is a fault
• Choose materials that can comfortably withstand
the expected levels of temperature
• New appliances should be submitted for testing
for BEAB approval.
Alternatives
Safety of electrical
equipment in respect of
protection from electric
shock can be improved
by operation at low
voltages using a
transformer or batteries.
Socket styles for electric lamps
Bayonet cap –
mostly used in UK
BC
(B22d)
Bayonet
Cap
Edison Screw –
widely used
G6.35
2 Pins
6.35 mm
apart
ES
(E27)
Edison
Screw
Diameter:
22 mm
Diameter:
27 mm
SBC
(B15d)
SES
(E14)
Small
Bayonet
Cap
Diameter:
14 mm
Other fittings mostly for low
voltage halogen
lamps
Small
Edison
Screw
Diameter:
14 mm
G4
2 Pins
4 mm
apart
GU10
Push and Twist
Pins 10mm apart
Antique (c. 1900) ceramic & brass
bayonet lampholder
E27 ceramic lamp holder
GU 5.3 max 50V
B22D holder
with switch
Switches
White in-line cord switch units with
rocker actuators. 2A rating.
PL00550: Clip-on. Double pole,
complies with NF C 61-120.
PL00551: Neutral terminal and
capacity for through conductor. Single
pole. Complies with CEE24.
Press switch push for on push for off
Often used in lamp bases
Single pole so only switches the live
side
Normally suitable for operation up to
2A = 500W
Cable strain relief components
Cable entry collet locks
cable in place where it
enters the appliance –
prevents cable being
pulled out
Nylon cable support
provides strain relief to
prevent cable kinking at
entry to appliance –
often seen on electric
irons.