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Load Calculations - Branch And Feeder Circuits (Chapter 1): Questions/Solutions
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Load Calculations - Branch And Feeder Circuits(Chapter 1): Questions/Solutions
What is the maximum continuous load that may be connected to a 20A, 120V
fuse? Right Ans - 20A x 80% or .80 = 16A (continuous loads are calculated
at 125% of the maximum current rating of the load. the reciprocal of 125% is
equivalent to 80%)
The voltage drop for a 208V, 1 ott circuit with a load of 28A, using No. 8
stranded copper conductors at the circuit length of 160' is....... Right Ans -
VD (Voltage Drop) = (2xLxRxI) / 1000, L- load center or total length in feet, R-
conductor resistance (NEC chapter 9, table 8), I- current.
(2x160ftx.776x80A)/1000 = 6.97V
The ampacity of a 120V, 1 ott load rated at 800VA is..... Right Ans - 800VA /
120V = 6.67A
Appliance Right Ans - utilization equipment, generally other than
industrial, normally built in standardized sizes or types, that is installed or
connected as a unit to perform one or more functions such as clothes washing,
air conditioning, food mixing, deep frying, or other purposes
Appliance branch circuits Right Ans - Branch circuits supplying energy to
one or more outlets to which appliances are to be connected. such circuits are
to have no permanently connected lighting fixtures that are not part of an
appliance
Demand factors Right Ans - ratio of the maximum demands of a system, or
part of a system, to the total connected load of a system or the part of the
system under consideration
General-purpose branch circuit Right Ans - Branch circuits that supply two
or more receptacles or outlets for lighting and appliances
What is the calculated load, in amps, for a 120V circuit supplying 8 recessed
fluorescent fixtures operating continuously? (Each fluorescent ballast is rated
at 0.5A.) Right Ans - 8 fixtures x 0.5A = 4A, 125% of 4A, 4Ax 1.25 = 5A
, What is the maximum number of continuous duty duplex receptacles that can
be connected to 20A, 120V circuit in a commercial building? Right Ans -
total circuit capacity = 20A x 120V = 2400VA, rating per receptacle = 180VA x
125% = 225VA, total loads that may be connected = (circuit capacity)/(rating
per receptacle) = 2400VA/225VA = 10.7 (round down) = 10 receptacles
What is the total load, in VA, for 4 small appliance branch circuits in a single-
family dwelling? Right Ans - 4 small appliances = 4 circuits, 4 circuits x
1500VA = 6000VA
What is the demand load for one household dryer with a nameplate rating
4.75kW? Right Ans - NEC section 220.54 household dryer load calculated at
either 5000VA or nameplate rating, whichever is larger, first convert the
nameplate dryer to VA and determine, which is larger
4.75kW x 1000 = 4750VA, 4750 < 5000VA
What is the demand load, in amps, for a small two-burner electric range with a
nameplate rating of 7kW, 1 ott, 240V Right Ans - Calculate 80% of the
nameplate rating, 7kW x 0.8 = 5.6kW, 5.6kW x 1000 = 5600VA, 5600VA/240V
= 23.3A
What is the ampacity of a water heater with a nameplate rating of 8400VA at
240V Right Ans - 8400VA/240V = 35A, 35A x 1.25 = 43.75A
What is the minimum conductor ampacity for four 1200W, 240V, 1 ott electric
baseboard heaters? Right Ans - 1200W x 4 heaters = 4800W = 4800VA,
4800VA/240V = 20A, 20A x 1.25 = 25A
What size copper branch circuit conductors are required to supply an air
conditioning unit with a nameplate rating of 18A, 240V, 3 ott? Right Ans -
find 125% of ampacity, 18A x 1.25 = 22.5A, looking at NEC table 310.16, 22.5A
= No. 10
Multi-outlet assembly Right Ans - type of surface, flush, or freestanding
raceway designed to hold conductors and receptacles, assembled in the field
or at the factory.
The load for 8' of multi-outlet assembly used simultaneously is Right Ans -
1 outlet considers 180VA, 8 x 180VA = 1440VA
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