GE SHOWBIZ - Manual (Page 58)

GE LIGHTING - SHOWBIZ™ ENTERTAINMENT LIGHTING CATALOGUE 110
Surge Current
The cold resistance of a halogen studio lamp is approx. 1/17 of its value in normal operation. On switch on,
theoretically a surge current of 17
√
2 x the normal current would flow and depending on the thermal mass of
the filament* this will fall to the lamp normal current in approx. 1 sec. In practice this maximum theoretical
current does not appear due to (a) switch on does not always occur at the peak of the AC voltage, (b) the
supply has some impedance which is comparable with the cold resistance of high wattage lamps, i.e.
maximum possible surge current where V is the applied voltage and Z is the sum of the lamp cold resistance
and the supply impedance.
Typically supply impedance is the order of 0.3 ohm and lamp life is based on testing with such a supply. In the
rare cases where the line impedance is lower than this figure, an adverse effect on life may be encountered
particularly with high wattage types, due to the then extremely high surge current on switching.
lamp type cold max. surge current (amps) normal
resistance line impedance = operating
(ohms) 0 ohms 0.1 ohms 0.3 ohms 0.5 ohms current
240V 10kW 0.34 1000 774 530 405 41.5
240V 5kW 0.7 486 424 340 283 20.8
115V 5kW 0.15 1085 650 360 250 43.5
240V 2kW 1.7 200 189 170 154 8.35
117V 2kW 0.41 404 324 233 182 17.1
240V 1kW 3.4 100 97 92 87 4.15
GE LIGHTING - SHOWBIZ™ ENTERTAINMENT LIGHTING CATALOGUE 111
Fusing of Tungsten Halogen Studio and Theatre Lamps
A lamp normally fails at end of life by fusing of the filament. Often an arc then forms and as there is
little resistance to limit the current this rises to a very high value which if maintained can result in a
serious overload on the envelope and seals. This might result in the lamp shattering. A quick acting
high breaking capacity fuse must be connected in the supply line in all applications. Suitable types are
given in BS88 (IEC 60269), IEC 60127 or IEC 60241.
lamp fuse (rated current)
power (amps)
(watts) 100-115V 115-130V 220-250V
500 6 6 4
650 10 6 4
1000 16 (15 UK) 10 6
1500 20 16 (15 UK) 10
2000 25 (30 UK) 25 (20 UK) 10
2500 35 (30 UK) 25 (30 UK) 16 (15 UK)
5000 63 (60 UK) 50 25 (30 UK)
10000 125 100 50