120608 voltage drop

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Voltage Drop

Voltage drop is the reduction in voltage in an electrical

circuit between the source and load. It is caused by the

current flow through conductors resistance (Ohms law).

What is Voltage Drop

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Voltage Drop

• Operating voltage at electrical equipment will be less than the output

voltage of the power supply.

• Inductive loads (i.e. motors, ballasts, etc.) that operate at voltage below

its rating can overheat resulting in shorter equipment operating life and

increased cost.

• Under-voltage for sensitive electronic equipment such as computers,

laser printers, copy machines, etc., can cause the equipment to lock up

or suddenly power down

Why is Voltage Drop is undesired?

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Voltage Drop

• VD=((2*K*L*I)/CM)*.866 (only for 3-phase)• VD= Voltage drop

• K=Resistivity 12Ω for copper

• L= Length one way

• I= Current in amps

• CM= Circular mill area of wire (Chapter 9 Table #8 of NEC)

How to Calculate voltage Drop?

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• We have a Voltage Drop Calculator saved in:

• T:\Engineering\Details and Schedules - Autocad\Electrical Schedules

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Voltage Drop

• ALL 120V BRANCH CIRCUITS IN EXCESS OF 75’ & 277V BRANCH

CIRCUITS IN EXCESS OF 120’ SHALL HAVE CONDUCTOR SIZE INCREASED

A MINIMUM OF 1 CONDUCTOR SIZE.

Example

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Voltage Drop

• National Electrical Code (NEC)

• Section 210.19.A.1 & 215.2.A.3 requires that voltage drop shall not

exceed TOTAL 5% at the farthest outlet of connected load.

• 2% feeder conductors.

• 3% branch circuit wiring.

Voltage Drop is code required

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Voltage Drop

• It is required by energy calculation:

• Comcheck

• T24

• Florida

Voltage Drop is code required (cont.)

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Voltage DropCONCLUSION . . .

THANK YOU.