Wire Sizing
NEC® Table ___ is used to size the conductor installed between the ground bar in a service panel and the metal housing of a 3-phase motor.
NEC 250.122
The connection between the grounded circuit conductor and the equipment grounding conductors at the main service is the Code definition of
Main Bonding Jumper
A 277/480-volt, 3Ø, 4W feeder has been installed in EMT between a 3-pole breaker in a main breaker panelboard and another panel. If one of the ungrounded conductors touches the EMT, this is considered to be a ___.
Ground Fault
Determine the minimum size overload protection required for a 480-volt, 3-phase, 15 hp, continuous duty motor given the following information.
* Design B * temperature rise - 50ºC
* service factor - 1.12 * actual nameplate rating - 18 amps
20.7A
18 x 1.15 = 20.7 amps
What are the 2 main multipliers for motor OCPDs?
175% (For DETD) & 250% (For ITCB)
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
A 120/240-volt, 1-ph, 3-wire service is to be installed to serve a 60-Amp service. The conduit will have two ungrounded conductors and one grounded conductor. The ungrounded conductors will be 6 AWG copper conductors. The load on the neutral will be 35 amps. The smallest neutral that can be installed is a ___ AWG conductor.
8 AWG - 250.102(C)(1)
&
T310.16 (B)
As circuit resistance ___, the time it takes for an OCPD to operate decreases.
Decreases
Motor Nameplate Information: 115/230-V 1Ø 3 hp
Supply: 1-pole breaker in a 120/240-V, 3-ph, 4-W panel
What minimum size SJ cord is needed to connect this motor?
7 AWG SJ Cord
T/F
Most motors require a local disconnect switch
False
A grounded conductor is run in four parallel conduits with 4 sets of 250 kcmil service conductors to a 1000-amp 277/480-volt, 3-ph, 4-w switchboard. The minimum size of the neutral in each conduit is ___ AWG or kcmil.
for 250 kcmil: T.250.102(C)(1) 2 AWG vs
1/0 minimum for parallel 250.24(D)(2)
When a service-entrance conductor consists of one set of 500 kcmil conductors, the main bonding jumper shall be ___ AWG in size.
1/0
When a 3Ø, 4-W supply system delivers 120/208 volts, the system has a neutral.
True
Nameplate Info: 10 HP, 3 Phase
Supply Info: 480/277-volt, 3Ø, 4-wire panelboard.
The minimum size branch circuit conductors for the motor are ___ AWG.
14 AWG
T.FLC =11 - 11 X 1.25 = 13.75 = 14 A 14 AWG
What is the process for finding and setting overload values for a motor
1) Use Nameplate FLA
2) Find Service Factor/Temp Rise
3)Use Correct Multiplier (115%/125%)
What is the smallest size wire permitted to be used as a system bonding jumper in an 800-A fused safety switch? The safety switch is fed from a transformer with four parallel sets of 3/0 AWG wire.
2/0 AWG
167,800 cm x 4 = 671.2 kcmil 2/0 AWG
Section ___ of the NEC® states that bonding shall be provided where necessary to ensure electrical continuity and the capacity to conduct safely any fault current likely to be imposed.
NEC 250.90
A circuit is installed in EMT and compression fittings are used. A separate EGC is NOT installed in the conduit. If a ground fault occurs and some couplings were never tightened properly, compared to normal operation, the fault current will be ___ and the OCPD will take ___ time to open.
Lower More
When a motor branch circuit consists of 12 AWG wire and 60 amp fuses, the largest equipment grounding conductor required by the NEC® is ___ AWG.
12 AWG
The rotating magnetic fields in a 3Ø motor are ___ electrical degrees apart.
120 Degrees
What is the smallest size copper wire permitted to be used as a GEC to building steel from a 1200-A fused safety switch? The safety switch is fed from a transformer with four parallel sets of 350 kcmil wire.
3/0 AWG
A 1200-ampere, 3-phase 208/120-volt service is supplied with four parallel sets of size 350 kcmil ungrounded conductors. The minimum size MBJ permitted is ___ AWG or kcmil.
4/0
4 x 350 kcmil = 1400 kcmil 1400 kcmil x 0.125 = 175 kcmil 4/0 AWG
The NEC® does not require the _____ conductor to be larger than the derived ungrounded conductors.
Grounded
Motor - 240V, 3 Phase, 7 1/2 HP
The largest permitted breaker that can be installed in the panel for this motor is ___ A.
60 A Breaker
Table FLC = 22 amps
22 X 2.5 = 55 A
What are the 3 distances for motor feeder taps?
10', 25', & over 25,