2012/01/07 at 6:04 pm #10751elec masterParticipant
This voltage drop calculator will provide an approximate value for use in project design and it is based on the following public domain formula.
NEC Rules controlling Voltage Drop:
NEC article 210.19(A)(1) FPN No.4 and 215.2(A)(3) FPN No.2 :
These FPN’s (Fine Print Notes) suggest that a design with no more than 3% voltage drop for feeders and no more than a total of 5% voltage drop in branch circuits to the farthest outlet will provide reasonable efficiency at operation.
Note: Even though FPN’s (Fine Print Notes) in this case are not code requirements but recommendations, it is still good engineering practice to closely follow these guidelines
NEC article 647.4(D):
For Sensitive Electronic Equipment, The voltage drop on any branch circuit shall not exceed 1.5 percent and the combined voltage drop feeder and branch-circuit conductors shall not exceed 2.5 percent.
NEC article 647.4(D) (1):
For Fixed Equipments, The voltage drop on branch circuits supplying equipment connected using wiring methods in Chapter 3 shall not exceed 1.5 percent and the combined voltage drop of feeder and branch-circuit conductors shall not exceed 2.5 percent.
NEC article 647.4(D) (2):
For cord-connected equipment, The voltage drop on branch circuits supplying receptacles shall not exceed 1.0 %. For the purposes of making this calculation, the load connected to the receptacle outlet shall be considered to be 50 percent of the branch-circuit rating. The combined voltage drop of feeder and branch-circuit conductors shall not exceed 2.0 %.
NEC Article 695.7:
For Fire pumps, the voltage at the controller line terminals shall not drop more than 15 percent below normal (controller-rated voltage) under motor starting conditions. The voltage at the motor terminals shall not drop more than 5 percent below the voltage rating of the motor when the motor is operating at 115 percent of the full-load current rating of the motor.
Exception: This limitation shall not apply for emergency run mechanical starting. [NFPA 20, 6.4]
This spreadsheet includes three different worksheets as follows:
1-Voltage Drop Calculator worksheet
to read more and download your copy , please follow the link:
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