Eaton Cutler Hammer MN05001002E Installation Manual

Intelligent Technologies QCPort System Install ManualNovember 2005MN05001002E For more information visit www.eatonelectrical.com Page 22Sizing CalculationA power supply that is not end connected creates two sections of cable. Because of this,each section needs to be evaluated separately. The equation sums the calculated dropfor each device and compares it to 4.65V.SUM {[(L n x Rc) + (N t x (0.005))] x In } <= 4.65VTerm Definition Term DefinitionL n L = The distance (ft) between thedevice and the power supply,excluding the drop line distance.n = The number of the devicebeing evaluated, starting with 1 forthe device closest to the powersupply and increasing by 1 for thenext device.(0.005) The nominal-contact resistance used forevery connection to the trunk line.Rc Long Run0.021 (ohm/ft)QCPort Interconnect0.105 (ohm/ft)4.65V The maximum voltage drop allowed.This is the total cable system voltagedrop of 5.00V minus 0.35V reserved fordrop line voltage drop.N t The number of taps between thedevice being evaluated and thepower supply. For example:• When a device is the firstone closest to the powersupply, this number is 1.• When a node has one devicebetween it and the powersupply, this number is 2.• When 10 devices existbetween the evaluated nodeand the power supply, thisnumber is 11.For a device attached as a dropfrom a device, the currents for thetrunk and drop device should besummed and used with theequation only once.In I = The current drawn from the cablesystem by the device. For currentswithin 90% of the maximum, use thenominal device current. Otherwise, usethe maximum rated current of the device.For a device attached as a drop from adevice, the currents for the trunk anddrop device should be summed andcounted as one tap.n = The number of devices beingevaluated, starting with 1 for the deviceclosest to the power supply andincreasing by 1 for the next device.