Wire Sizing
A single-pole breaker in a 120/240-V, 1-ph, 3-W panel supplies power to a motor circuit consisting of the smallest permitted conductors. The largest permitted DETD fuses are installed in a safety switch for the 115/230-V, 1Ø, 1 hp motor. The minimum size EGC permitted for this installation is ___ AWG. *
14 AWG
Table FLC = 16 amps -> 1.75 X 16 = 28 30 A fuse 10 AWG
versus 16 X 1.25 = 20 A 14 AWG
EGC not req’d to be > 14 AWG
NEC® Table ___ is used to size the conductor installed between the ground bar and the neutral bar in a service panel. *
NEC 250.102(C)(1)
An effective ground-fault current path has ___. *
Continuity, Sufficient Ampacity, Low Impedance
A motor has the following nameplate information:
208V 3ph 15 HP 42 Amps 1.15 Service Factor
The initial overloads were not sufficient to run the motor. What is the new rating of the overloads? *
58.8 A
NEC 430.32
A 3-phase motor can be reversed by swapping any two circuit conductor connections at what location? *
Load side of starter, Terminal box at the motor, line side of starter, Load side of safety switch
The smallest THHN/THWN copper grounded conductor that can be installed for a service is ___ when the ungrounded conductors are 1/0 THWN/THHN copper and the load on the neutral is expected to be 120 amps.
1 AWG
T. 250.102(C)(1)_vs_T. 310.16
Rod and pipe electrodes are defined and described in ___. *
NEC: 250.52(A)(5)
How does grounding prevent an electrical fault? *
It Doesn't
The nameplate for a 15 HP, three-phase motor shows an FLA of 35 amps at 230 volts. What minimum size SOO cord is required to connect the motor to the branch circuit? *
4 AWG SOO Cord
Table FLC = 42 amps -> 42 X 1.25 = 52.5 A 4 AWG
Circuit conductors (14 AWG) are installed between a 3-pole, 40-A circuit breaker in a panel and a motor. The circuit breaker protects the conductors against ___. *
Short circuit, Ground fault
Motor Nameplate Information: 208-230/460-V 3Ø 100 hp
Supply: 3-pole breaker in a 120/240-V, 3-ph, 4-W panel
Minimum size circuit conductors are ___ AWG/kcmil. *
Table FLC = 248 amps -> 248 X 1.25 = 310 A -> 350 kcmil
The minimum size of an equipment grounding conductor for a circuit protected by an automatic overcurrent device rated at 100 amperes is a ___ AWG wire. *
8 AWG
NEC: 250.122 (Table
If a GEC were to be installed inside a “conduit” to protect it from physical damage, which "conduits" may be used? *
EMT, IMC, Sch. 80 PVC, RMC
The smallest permitted circuit conductors are to be installed to feed a 2 hp, 115/230-V, single-phase motor. The circuit is supplied from a 1-pole breaker in a 120/208-V, 3-ph, 4-W panel. The maximum permitted size ITCB was installed for the motor circuit. Under these conditions, the minimum size EGC permitted is ___ AWG. *
10 AWG EGC
Table FLC = 24 amps -> 2.5 X 24 = 60 A breaker 10 AWG
24 x 1.25 = 30 A -> 10 AWG at 75º terminations EGC not req’d to be > 10 AWG
“Heaters” are installed in motor starters to protect ___. *
The motor against overload
The branch circuit conductors against overload
A grounded conductor is to be pulled in with 500 kcmil THHN/THWN aluminum conductors as part of a 277/480-volt, 3Ø, 4-W service to a 300-amp fused safety switch. The maximum unbalanced load on the neutral will be 140 amps. The minimum size of the neutral is ___ AWG aluminum. *
3/0 AWG
140 amps -3/0 AWG vs T.250.102(C)(1) - 1/0 AWG
The minimum size of a grounded conductor in a conduit is based on ___.
The size of the largest ungrounded conductor
The load the neutral must carry
Electrical systems that are grounded shall be connected to earth in a manner that will limit the voltage imposed by what 3 things? *
Line surges, Lightning, Unintentional contact with higher-voltage lines
Motor: 7 1/2 HP 208V 3 Phase
The branch circuit for the motor is supplied from a 120/208-volt, 3Ø, 4-wire panelboard. The maximum size ITCB that can be used on the motor branch circuit is ___ A. *
70 A ITCB
T.FLC=24.2 24.2 X 2.5 = 60.5
Size the overloads for a motor with the following nameplate information:
480 Volt - 3-phase 5 HP 4 Amps 50°C temperature rise *
4.6 A
A 225 KVA, 480 delta to 208/120-volt, 3-ph, 4-w transformer is to be installed. One conduit will be installed between this 225-amp panel and the transformer. The conduit will contain 3 each 4/0 ungrounded conductors and the smallest permitted size grounded conductor. Almost all the connected load is 3-phase. The smallest grounded conductor you can install in the conduit to the 225-A PB is ___ *
2 AWG
250.102(C)(1)
Determine the minimum standard size (AWG or kcmil) main bonding jumper required for a service with two sets of paralleled 750 kcmil conductors.
2 x 750 kcmil = 1500 kcmil x 121/2% = 187.5 kcmil
187.5 kcmil from Table 8, Chapter 9 (next larger size) 4/0 AWG
4/0 AWG is the minimum size main bonding jumper permitted for this service.
T/F
An overload occurs when an electrical conductor or equipment is operated in excess of its current rating. *
True
Motor Nameplate Information: 208-230/460-V 3Ø 200 hp
Supply: 3-pole breaker in a 120/208-V, 3-ph, 4-W panel
Minimum size circuit conductors are ___ AWG or kcmil where 3 paralleled sets of conductors are used. *
Table FLC = 528 amps -> (528 X 1.25) ÷ 3 = 220 A 4/0 AWG at 75º terminations
The ___ is the rotating part of a 3Ø motor. *
Rotor