9140053447 Rev. 0
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LHD2 Series EMERGENCY TWO HEAD LED EXIT
WIRING CALCULATIONS FOR VOLTAGE DROP PROTECTION
IN EMERGENCY LIGHTING SYSTEMS
TO DESIGN A PROPER EMERGENCY LIGHTING SYSTEM, CIRCUIT RUNS MUST BE OF SUFFICIENT SIZE TO MAINTAIN A PROPER
OPERATING VOLTAGE TO ALL LAMPS. MAXIMUM ALLOWABLE VOLTAGE DROP SHOULD NOT EXCEED 5%. PROPER WIRE SIZE
IS DETERMINED FROM THE FOLLOWING FORMULA, TABLE AND EXAMPLE SHOWN BELOW.
L =
CM x EI
CM=
I x 22 x L
I x 22
EI
CM = WIRE SIZE IN CIRCULAR MILLS
I = LOAD IN AMPERES (EMERGENCY MODE)
L = LENGTH OF WIRE RUN. (UNIT TO REMOTE LOAD)
EI =
I x 22 x L
I=
CM x EI
EI = MAXIMUM ALLOWABLE VOLTAGE DROP. (5%)
CM
L X 22
USING THE ABOVE FORMULA AND HAVING CALCULATED THE CIRCULAR MILLS REQUIRED TO CARRY THE SPECIFIED LOAD AT
A PREDETERMINED AND ALLOWABLE VOLTAGE DROP, THE FOLLOWING CHART WILL IDENTIFY THE NECESSARY WIRE GAUGE
FROM THE CORRESPONDING CIRCULAR MILL SIZE LISTED.
WIRE GAUGE
AMPERE CAPACITY
OHMS PER 1000 ft
CIRCULAR MILL SIZE
12 20
1.586
6,530
10 25
.9972
10,380
8 35
.6271
16,510
6 50
.3944
26,250
4 70
.2480
41,740
EXAMPLE:
WHAT SIZE SHOULD BE USED FOR A 6-VOLT CIRCUIT TO TRANSMIT A CURRENT OF 4 AMPERES A
DISTANCE OF 75 FEET WITH A VOLTAGE DROP OF NOT MORE THAN 5%?
EI = MAXIMUM ALLOWABLE VOLAGE DROP 5% OF SELECTED VOLTAGE:
USING 6 VOLTS x .05 = .3 VOLTS.
USING THE FORMULA AND SUBSTITUTING THE GIVEN QUANTITIES:
CM = 4 x 22 x 75 = 22000 CIRCULAR MILLS NEEDED. (USE #6 WIRE)
.3
NOTE:
SMALLEST PERMISSIBLE WIRE SIZE FOR SYSTEMS UNDER 50 VOLTS IS #12 FOR EMERGENCY LIGHTING EQUIPMENT
UNDER ARTICLE 720-4 OF THE NATIONAL ELECTRIC CODE
.
6 VOLT
WIRE WATTS
SIZE 12
24 60
#12 47
23 9
#10 75
37 15
#8 119 59 23
#6 189 94 38
WIRING DISTANCE IN FEET
Summary of Contents for LHD2 Series
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