Second Year 2nd semester mid-term
Between the transfer switch and the disconnect switch for the generator input, you are required to install _____ -inch conduit.
1 1/2
Each winding set in a Group III, B-B transformer has a turns ration of ______.
10:1
A wye-connected transformer secondary has line to line voltage of 208 volts. The voltage across each winding is _____ volts.
120
From Y2 annex D you have selected a catalog number 21110 transformer to boost the circuit voltage from 208 to 240 to serve a load. The 208 volt circuit originates in a 120/208 volt 3 phase 4 wire panelboard. The largest breaker permitted by the NEX for this circuit is a 2 pole ____ A.
150
A transformer with a k rating of ____ should be used for computer rooms
20
A 480x120/208 volt transformer is connected to a line with a voltage of 518. if compensating taps are not used what will be the secondary line voltage?
224
A 480- delta to 240 delta transformer, without taps, is connected to a 510 volt line. The line to line voltage on the secondary will be ______ volts.
225
Where a transformer is installed in a vault on the 3rd floor of a highrise building and is not protected by an automatic fire suppression system, the minimum fire rating for the floor is _____
3
A circuit supplied from a 225 amp 480 volt breaker connects to the primary of a225 kva 480- 120/208 volt 3 phase 4 wire transformer. the transformer feeds a panelboard with a 200 amp main breaker. the length of the secondary conductors between the transformer and the main is 13 feet. these conductors must be atleast _____ in size.
3/0
The Type VE luminaires in the BCEs kitchen contain a total of ____ lamps
4
The 10 awg thhn/thwn copper circuit conductors are connected to a3 pole breaker in a 120/240 volt, 3 phase 4 wire panelboard. The circuit serves a load that draws 14.5 amps. The maximum distance between the panel and the load is ____ feet where the manufacturer limits the voltage to +%5. The manufacturer's nameplate rating on the equipment is 240 volts. use K= 11.7 to solve this problem.
424
A "bank" of three individual single phase transformers is to be connected to deliver 277/480 volts. Each of the transformers is rated at 150 KVA. The total rating of the bank is ______ KVA.
450
When a 120/208 volt 3 phase 4 wire supply system (typically a transformer) delivers power to a load, the line current equals _______.
I coil
An electrical system must be designed using equipment that meets or exceeds the short circuit current rating available during a fault. T/F`
True
Optional accessories for generator sets may include _____. i. audio visual alarms ii. common failure relay kits iii. line circuit breakers iv. low fuel switches
all of these
Optional standby systems, as classified by the AHJ would generally be required for which of the following? i.HVAC equipment ii. refrigeration equipment in food stores iii computer equipment in office buildings
all of these
Selection criteria considerations for generator include _____ requirements. i. voltage ii.fuel source iii isolation pad iv full load
all of these
When a supply voltage is to be changed from 102 V to 120 V a buck boost transformer is connected as ____- tio deliver the proper voltage to the 120- volt load.
an autotransformer
transfer switches are categorized as _____. i. open transition ii. closed transition iii. closed transition soft load
any of these
when installing conduit system in an area designated for a generator installation, careful planning is required to not ingibit the installation or operation of the ____ sytems. i.cooling ii. exhast iii. fuel
any of these
To deliver adequate fuel to diesel fueled generators sets, without clogs and without injecting air into fuel lines, ______ piping is used for the fuel lines.
black iron
Common transformer mountings include _____ i. pole or vault ii. floor or platform
both i and ii
Section 240.21(c)(2) in the NEc is the 10 foot rule. This section requires that the secondary conductors be 10 feet or shorter in length, be installed in a reaceway and _____/ i. be sized to carry the load ii. have an ampacity that is > the rating of the circuit breaker or fuses at the end iii. have an ampacity that is > ( PRI OCPD/10)x(Eprimary line/ E sec line)
i, ii and iii
Some typed of transformers are liquid filled. The liquid helps to dissipate the heat generated by the transformer windings. T/F
true
The connected load on the secondary of a transformer causes current to flow in primary. T/F
true
an auto transformer may be used to ____supply circuit voltages. i.boost ii.buck
both i and ii
Which of the following are linear loads? i.hid light ii. booster heater for a dishwasher
a booster heater for a dishwasher
A _____ output could be produved by connecting three individual 240x 480 --- 120/240 volt single phase transformers into a bank i. 240 volt 3 phase 3 wire ii. 120/240 volt 3 phase 4 wire
either i or ii
A piece of equipment has arrived at the job its nameplate indicates that it is rated to operate at 230 volts. You already run a 2wire circuit form a 2 pole breaker in a 120/208 volt 3 phase 4 wire panelboard to supply the equipment. You should connect the equipment _____.
through a 120/240-- 12/24 Buck boost transformer
For a wye system, the line voltages and coil voltages ______ equal. Are/are not
are not
Which of the following are linear loads? i. hid lighting ii. computers
neither i or ii
small transformers that are back fed can experience ______. i. high inrush currents ii. nuisance tripping of primary OCPD's
both i and ii
when buck boost transformers are connected to ______ the input voltage the primary and seco dary voltages are subtractive. BUck/Boost
buck
1500 kV= _______ volts
1,500,000
The catalog number for a5 KVA 120x240-- 12/24 V transformer is ______.
11111
The ampacity of coductors from the generator to the first distribution device containing overcurrent protection shall not be less than ____ percent of the nameplate current rating of the generator,
115
A 45 KVA 480 to 208y/120volt dry type transformer is located in front of a plywood telephone equipment board that is attached to the wall. The general rule in the NEC is taht the minimum clearance from the transformer to this combustible wall covering is _____ inches.
12
For emergency systems where internal combustion engines are used as the prime mover an on site fuel supply shall have sufficient fuel supply for not less than ____ hours full demand operation of the system
2
Type _____ buildings have fire resistance ratings from o to 2 hours.
2
When a 120/240, 3 phase 4 wire open delta bank of transformers delivers power to a load, the b phase to neutral voltage is ______ volts.
208
A 3 phase generator is supplying 27 amps to a 480 volt 3 phase load. The generator is supplying _______ wattes to the load.
22,447
When a 3 phase, 4 wire supply system ( typically a transformer) delivers 120/240 volts, the system has line-to-line voltages that are ________.
240
A transformer supplies power to a 240 volt, 3 phase non-continuous 32.286 KVA load. The smallest secondary circuit conductors that can be used are _____ AWG.
4
a 7200 to 4160 volt 3 phase 150 KVA transformer is installed in a supervised location and is supplied from a feeder tap that is protected with a 3 phase fused safety switch. The transformer supplies power to a circuit breaker in an enclosure. As limited by NEC 450.3, the maximum size CB permitted to be installed in the enclosure is ____ amps. The transformer Z=7%
50
The maximum size ITCB permitted to protect the primary of a 4260 to 480 volt single phase 75 KVA transformer is ____ amps. as required by NEC 450.3. The transformer has an impedance of 4.3% and is installed in a supervised location. Secondary protection is NOT required.
60
A 15 KVA single phase load has a rated voltage of 208 volts. This load will pull _____ amps when supplied from a circuit in a 120/208 volt 3 phase 4 wire panelboard.
72.1
Emergency systems as classified by the AHJ would generally be required for which of the following? i.exit and egress lighting in hotels ii. 911 communication systems iii,= elevators in hospitals
all of these
which of the following would be considered non-linear loads? i. ac variable speed drives for motors ii. welders iii. desktop computers
all of these
A 3 phase 240 load is to be supplied with a 3 phase 3 wire circuit that originates from a 120/208 volt 3 phase 4 wire panelboard. You will install Group II "buck boost" transformers that will be field connected per connection diagram ____- Y2 annex D
B-B
Three individual 240/480------ 120/240 volt single phase transformers could be connected to produce a _______. output i. 240- volt 3 phase 3 wire ii. 120/240 volt 3 phase 4 wire iii. 120/208 volt 3 phase 4 wire`
i, ii, and iii
to produce an output of 12 volts a 120x240 volt primary 12/24 volt secondary transformer is connected as an ______.
insulating transformer
The BCEs walk in cooler / freezer is ____ powered from teh generator when normal power is lost.
manually
______ are manufactured with neutrals that are twice the size of a normal transformer.
non linear load isolation transformers
Temperature _____ is the amount of heat that an electrical component produces above the ambient temperature.
rise
Larger distribution transformers are commonly cooled by a liquid. T/F
true
The required clearances for proper transformer ventilation shall be clearly marked on the transformer.T/F
true
Generator set circuit breakers and fuses must open all ____ output circuit conductors.
ungrounded
A 277/480 volt 3 phase 4 wire service is supplied by a utility transformer that is located far away from the service equipment and the line to line voltage has dropped to 456 volts at the service equipment. The actual line to neutral voltage available at the servive equipment is _____ volts.
263
A piece or equipment has arrived at the job and its nameplate indicates that it is rated to operate at 240 volts. you have already run a 2 wire circuit from a 2 pole breaker in a 120/208 volt 3 phase 4 wire panelboard to supply the equipment . you should connect the equipment _____
Through a 120/240---16/32 Buck boost transformer
non linear load isolation transformers are readily available in standard k factor ratings of ______. i.20 ii.4 iii.13
all of these
ATS are _____ switches that coordinate the starting, running and stopping of emergency generator engine sets.
double-throw
Batteries for generator sets are usually of the ____ type.
lead-acid type
A 1.5 kVa single phae 120 to 24 volt transformer is fed by a branch circuit from a 20 amp circuit breaker. from a 20 amp circuit breaker. The secondary conductors are 4 AWG copper Thhn/thwn. Is secondary protection required for the transformer? comare the requirements of NEC 450.3 with 240.4 (F) Y/N
yes
Three sets of secondary conductors are run from a 225 KVA 480-- 120/208-volt 3 phase 4 wire transformer. set 1 feeds a panel board with a 100 amp main breaker set 2 feeds another panelboard with 200 amp main breaker set 3 feeds a safety switch fused at 100 amps Is this permitted by the NEC where triple lugs are installed in the transformer? Y/N
yes
you are installing a 150 KVA, 480 volt to 120/208 volt 3 phase transformer. IF the Z is 2.7% the available fault current on the secondary is _____ amps.
15421
Each winding set in a Group II, B-B transformer has a turns ratio of _____.
15:2
When a 3 phase load is drawing 48 amps at 208 volts, this is a ______ load.
17.3 kva
A single-phase, 480 volt duct heater is rated for 10 KVA. It is being fed from a 277/480 volt 3 phase panel. The duct heater will draw _____ amps.
20.83
A particular load has a nameplate rating of 51.2 at 240 volts. The circuit you habe available to supply the load is 208 volts. The catalog number for a B-B transformer that can operated tha load at its rated voltage is _____-.
21109
A wye connected generator has a line-line voltage of 380 volts. What is the voltage across each winding?
219
A bank of transformers will require that three transformers with ratings of atleast _______ KVA each be used to supply enough power at 120/240 volts to a 69 KVA 3 phase load.
23
The primary of a 112.5 KVA transformer is 480-volt delta and is delivering 100 amps to a 3 phase load. GIven these conditions, ______ amps of current are flowing through each primary winding.
29
Where a transformer vault is not protected by an automatic fire suppression system the minimum fire rating for the walls is _____ hours.
3
The maximum size fuse permitted to protect the primary of a 480 to 240 v single phase 15 KVA a dry type transformer is ____ amps. The secondary conductors are 6 awg copper thhn/thwn and over current protection is not provided on this secondary. Dont forget to check 240.4 (F) and 240.21 (C) in the NEC then pick the smaller permitted by artcle 240 or note 1 to T.450.3(B)
30
When used to buck or boost a 120 volt supply circuit A 1.5 KVA 120x 240-- 12/24 transformer can be connected to supply ____ different voltage outputs. The primary windings are supplied with rated, or close to rated voltage.
4
A 480-- 120/240 volt wye transformer is delivering power to a 3 phase load and has 75 amps of coil current flowing through each winding. The current flowing in each circuit conductor to the load is _______ amps.
75
two THHN/THWN copper circuit conductors are conected to a load that draws 11.9 amps. 176 feet of cable are run to the load and connected to a 2-pole breaker in a 480/277 volt 3 phase 4 wire panelboard. the smalles conductors you can install to the load are _____ awg where the specifications limit the voltage drop to 2.1%. use K= 10.86 to solve this problem
12
When a 480 volt 66 KVA 3 phase load is operated at its rated voltage, the current draw should be _______.
79.4
The minimum clearance from the bottom of a pole mounted 240 v transformer tot the ground is _____ feet.
8
When a 3 phase, 3 wire supply system delivers 480 volts, the system is ______ connected.
Delta
When a 120/208 volt, 3 phase, 4 wire supply system (typically a transformer) delivers power to a load, the coil current equals ________.
I(L)
When a 277/480 volt 3 phase 4 wire supply system ( typically a transformer delivers power to a load , the coil current equals
I(L)
A 3 phase 240 volt load is to be supplied with a 3 phase 3 wire circuit that originates from a 120/208 volt 3 phase 4 wire panelboard. The 3 phase load is rated at 30 KVA. The smallest Group II transformers you can select for this load is _____ KVA. Y2 Annex D
1
Although NEC 450.3 permits a certain OVPD rating for transformer protection,check 240.4(F) for secondary conductor protection requirements. The maximum size fuse permitted among those listed below to protect the primary of a 480 to 240 volt, single phase 500 VA dry type transformer is ____ amps. The secondary conductors are 14 awg copper thhn/thwn and overcurrent protection is not provided on this secondary/
3
A 3 phase circuit supplies power to a 23.1 A load. A 3 pole breaker in a 480/277 volt 3 phase 4 wire panel provides this power through 196 feet of 12 awg MC cable. The voltage applied to the load is _____ volts. The K value for this cable installation is 11.7.
466
Between the transfer switch and the disconnect setich for the generator input, you are required to install a total of _____ conductors in the conduit.
5
To limit the voltage drop to 3%, ______ AWG are the minimum size thhn/thwn copper branch circuit conductors permitted. The circuit is 480 volt, three phase and serves a 25 KVA load. The load is located 420 feet from the panel. Use K = 12 to solve this problem.
6
When a 277/480 volt 3 phase 4 wire supply system ( typically a transformer) delivers power to a load, the coil ( or winding) voltage equals_______.
E(L)/1.732
When a 120/240 volt 3 phae 4 wire supply system delivers power to a load the coil or winding current equals _____
I(L)/1.732
A 2 wire circuit is run from a 2 pole breaker in a 120/240 volt 3 phase 4 wire panelboard to supply a pieve of equipment. The equipment nameplate indicates that it is rated to operate at 225 volts. You should connect the equipment _____.
Through a group II buck boost transformer
A 120/240 volt single phase 3 wire panel is fed from a 50 KVA single phase transformer that has Z=2.8% on its nameplate. The transformer is supplied power from a 2 pole breaker in a 277/480 volt 3 phase 4 wire panel. If X1 and X4 are connected together using a 4/0 awg copper jumper ______ amps of current will flow through the 4/0.
7440
Transformer vaults shall be constructed of materials with a minimum fire resistance of ____ hours.
3
