Specifications

Inselfampliedspeakers,thesmallampliersbehindeachspeakerarepoweredwith24VDC,andtheseampliers
haveadenitecurrentdraw,whichmeansthataspeciclengthofrunandwiresize(whichinturncreateacertain
resistance)willhaveanimpactontheamountofcurrent,measuredinamperes,ormilliamps,thattheamplierswill
actuallyreceive.Byimposingalargercurrentdrawthanthewiringcanhandle,thesystemwill“see”adropinvoltage
andcurrentow.Mostdevicesspecifyaminimumoperatingvoltageandcurrentrequirement.
All of these considerations are basically gyrations of Ohm’s Law. And, unless the wire is sized correctly for the current
drawandlengthofrun,strangethingsmayhappenwhenyoureupthesystem.Volumewillbelowerthanexpected,
sound may drop in and out, or, in extreme cases, it may not work at all!
Table#2,ataglance,giveswiresize,lengthofrunsandcurrentdrawfora10%dropinvoltagefor24VDCsystems.A
voltagedropof10%represents21.6VDC,wellwithintheoperationalrangeofWheelock’s24VDCpoweredproducts.
Asanexample,let’ssayyourinstallationcallsforten8”selfampliedceilingspeakers.Thedistancebetweenthepower
supplyandthelastspeakeronthelineisabout170feet.Forsimplicityandevengreater“headroom”,let’sassumean
“endoftheline”situation—thatis,viewthesituationasifall10speakerampliersweresittingoutthereattheendof
a 170 foot run of wire.
If,atfullpower,atypicalselfampliedspeakerdrawsabout105mA,thefullconnectedloadwilldraw105mAx10
speakers=1050milliamps,(1.05amps).Lookingatthechart,1100milliampscanbedrawnthrough170feetof#18
gauge wire. The correct wire size, therefore, is #18 AWG.
1. Doubling the current draw reduces cable length 1/2. Halving the current draw
doubles cable length.
  2. Doublingthevoltage(ie.48VDC)doublescablelength.Halvingthevoltage
   (ie.12VDC)reducescablelength1/2.
3. 1000 milliamps — 1.0 amp.
Table #2
2 WIRE COPPER CABLE LENGTHS FOR 24 VDC POWER LINES
AT A 10% DROP IN VOLTAGE
AWG CURRENT DRAW (MILLIAMPS) AWG
Size 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 Size
10 12000 6000 400030002400 2000 1720 1500 1335 1200 1090 1000 925 860 800 10
 12 7500 3750 250018801500 1250 1070 940 835 750 680 625 570 535 500 12
 14 4800 2400 16001200 960 800 690 600 535 480 435 400 370 345 320 14
16 3000 1500 1000 750 600 500 430 375 335 300 275 250 230 215 200 16
 18 1880 940 630 470 380 310 270 235 210 190 170 155 145 135 125 18
 20 1200 600 400 300 240 200 170 150 135 120 110 100 90 85 80 20
 22 375 375 250 185 150 125 110 95 85 75 70 65 60 55 50 22
 24 470 235 160 120 95 80 70 60 55 50 45 40 35 35 30 24
LENGTH IN FEET
NOTES: