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.

AlternativesSafety of electrical equipment in respect of protection from electric shock can be improved by operation at low voltages using a transformer or batteries.

           

           

SES (E14)Small Edison Screw

Diameter: 14 mm

           

          

BC (B22d)Bayonet

Cap

Diameter: 22 mm

           

           

SBC (B15d)

Small Bayonet

CapDiameter:

14 mm

           

            

ES (E27)Edison Screw

Diameter: 27 mm

           

           

GU10Push and Twist

Pins 10mm apart

           

           

 G6.352 Pins 6.35 mm apart

           

          

G42 Pins

4 mm apart

Socket styles for electric lamps

Bayonet cap – mostly used in UK

Edison Screw – widely used

Other fittings - mostly for low voltage halogen lamps

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.