New Mexico CID Low Voltage Special Systems (Under 50 Volts) Examination

Per NEC 2020 250.20(A), when must an alternating-current system of less than 50 volts be grounded?

• AOnly when the Authority Having Jurisdiction writes a special condition
• BWhenever the secondary current can exceed 8 amperes
• CWhen supplied by a transformer whose primary exceeds 150 volts to ground, when the transf…
• DNever; systems under 50 volts are exempt from Article 250

What is the minimum size of the copper bonding conductor or grounding electrode conductor for a communications primary protector under NEC 2020 800.100?

• A16 AWG copper
• B18 AWG copper
• C14 AWG copper
• D6 AWG copper

In a one- or two-family dwelling, NEC 2020 800.100 limits the primary-protector bonding conductor or grounding electrode conductor to a maximum length of:

• A6 feet
• B10 feet
• C20 feet
• D50 feet

Where an intersystem bonding termination required by NEC 250.94 is present, the preferred connection for a communications primary-protector bonding conductor is:

• AThe intersystem bonding termination at the service equipment
• BA driven rod that is intentionally isolated from the power grounding-electrode system
• CA cold-water hose bibb on the far side of the building
• DThe nearest metallic sprinkler main, without bonding to the electrical service

If a separate communications grounding electrode is installed because the protector bonding conductor would exceed the dwelling length limit, how must that electrode be connected to the power grounding-electrode system?

• ABond the two electrode systems together with a copper bonding jumper not smaller than 6 A…
• BNo connection is required if the rod measures 25 ohms or less
• CConnect them only through the equipment grounding conductor of a nearby receptacle
• DKeep them isolated so lightning current cannot enter the service

Under NMAC 14.10.4.12, what grounding-electrode installation is required on new construction when a concrete-encased electrode is not present?

• AA single 4-foot rod driven inside the electrical room
• BAt least 20 feet of 2 AWG bare copper in a continuous trench not less than 30 inches deep…
• CTen feet of 6 AWG insulated copper laid on grade and stapled to the foundation
• DNo electrode is required if all branch circuits are GFCI-protected

Where an outdoor CATV drop enters a building, the outer conductive shield of the coaxial cable must be bonded or grounded:

• AAs close as practicable to the point of entrance, typically with a listed grounding block…
• BAt the first TV set only, using the appliance equipment grounding conductor
• COnly if the drop is longer than 150 feet
• DTo a dedicated isolated ground rod that is not bonded to the power system

An ES-3 technician drives a new ground rod for a telephone protector 40 feet from the service and leaves it unbonded to the electrical grounding-electrode system. What is the principal hazard?

• AThe telephone pair will carry too much DC loop current
• BA large potential difference can appear between communications equipment and grounded pow…
• CThe Class 2 cable insulation voltage rating will be exceeded in normal operation
• DThe protector will not pass a 25-ohm megohmmeter test

Which cable marking identifies a general-purpose Class 2 cable that is not listed for riser or plenum use?

• ACL2P
• BCL2R
• CCL2
• DFPLP

Class 2 cable installed exposed in a plenum or other space used for environmental air must be which listing?

• ACL2X
• BCL2
• CCL2R
• DCL2P

NEC 725.136 generally prohibits placing Class 2 or Class 3 conductors in the same raceway or enclosure with electric light or power conductors unless:

• AThe power conductors are 20 amperes or less
• BThe Class 2 conductors are 18 AWG or larger
• CThe circuits are separated by a barrier, or another 725.136 permission (such as power int…
• DThe installer labels the raceway “mixed voltage”

Accessible portions of abandoned Class 2 and Class 3 cable must be:

• ATagged and left in place for future use
• BRemoved, per NEC 725.25
• CPainted red and documented on as-builts
• DSpliced into the nearest active homerun

Where Class 2 conductors are installed in “other applications” beside open power conductors, NEC 725.136(I) requires a separation of at least:

• A1/8 inch
• B1/4 inch
• C2 inches
• D12 inches

Power conductors are brought into a Class 2 equipment enclosure solely to supply that associated equipment. Unless a nonconductive sleeve or barrier is used, those power conductors must be routed to maintain a minimum separation of:

• A1/8 inch from the Class 2 conductors
• B1/4 inch (6 mm) from the Class 2 conductors
• C2 inches from the Class 2 conductors
• DNo separation is required inside listed equipment

What are the minimum voltage ratings required by NEC 725.179 for Class 2 cable and Class 3 cable?

• AClass 2: 30 volts; Class 3: 50 volts
• BClass 2: 150 volts; Class 3: 300 volts
• CClass 2: 300 volts; Class 3: 600 volts
• DBoth classes: 600 volts

A specification calls for CL2R in a vertical shaft. Which substitution is permitted by the NEC 2020 Class 2/3 cable substitution hierarchy?

• ACL2X in place of CL2R
• BCL2 in place of CL2R
• CCL2P or CL3P (or CMP) in place of CL2R
• DCMX in place of CL2R

Which UPS topology continuously regenerates a new AC output from the DC bus so the load never rides the raw utility waveform?

• ALine-interactive UPS
• BStandby (off-line) UPS
• COnline double-conversion UPS
• DFerroresonant tap-switching regulator without a battery

A Type 2 surge-protective device serving a low-voltage equipment rack is intended to be installed:

• AOn the load side of the service overcurrent device, typically at a panelboard or similar…
• BOn the line side of the service disconnect only
• COnly as a plug-in strip at the utilization equipment
• DIn series with the equipment grounding conductor

A shielded isolation transformer is used on a sound or data rack primarily to:

• ABreak common-mode noise and ground-loop paths between the primary and secondary
• BIncrease the secondary current available to Class 2 loads
• CConvert the circuit from Class 2 to Class 1 automatically
• DReplace the need for an equipment grounding conductor

A listed fire-alarm control unit is plugged into an unlisted office UPS that was sized only for a desktop computer. Why does that arrangement fail NFPA 72-2010 secondary-power rules?

• ANFPA 72-2010 forbids any use of a UPS
• BSecondary power must be a dedicated, supervised supply capable of the required standby pl…
• CThe UPS converts the initiating-device circuits from Class B to Class A
• DOffice UPS units operate at more than 50 volts, which is outside ES-3 scope

A 24-volt DC power-limited supply is connected across a 120-ohm load. What is the load current?

• A0.20 A
• B0.05 A
• C2.0 A
• D5.0 A

A 24-volt power supply delivers 0.50 A to a load. What power is delivered?

• A12 W
• B6 W
• C24 W
• D48 W

Three resistors of 100 Ω, 220 Ω, and 180 Ω are connected in series on a 24-volt control circuit. What is the total resistance?

• A55 Ω
• B180 Ω
• C500 Ω
• D4,000 Ω

A transformer with a 120-volt primary and a 24-volt secondary has which approximate turns ratio (primary to secondary)?

• A1:5
• B2:1
• C5:1
• D24:1

A voltage doubles from 1.0 V to 2.0 V across the same impedance. The voltage-ratio change in decibels is closest to:

• A2 dB
• B3 dB
• C6 dB
• D10 dB

Which statement correctly distinguishes AC from DC as used on ES-3 systems?

• ADC periodically reverses polarity; AC is unidirectional
• BAC periodically reverses polarity; DC is unidirectional
• CBoth AC and DC reverse polarity 60 times per second in the United States
• DClass 2 circuits are prohibited from using DC

In a coupling or filter circuit, a capacitor’s basic behavior is to:

• APass AC and block DC
• BPass DC and block AC
• CShort DC continuously while open-circuiting AC
• DConvert AC voltage to a constant magnetic field

Two 8-ohm loudspeakers are connected in parallel to a low-impedance amplifier output. What load does the amplifier see?

• A2 ohms
• B4 ohms
• C8 ohms
• D16 ohms

A silicon diode is placed in series with an AC source to produce pulsating DC. The diode is acting as a:

• AHalf-wave rectifier
• BZener voltage reference only
• CCenter-tapped full-wave bridge
• DStep-up autotransformer

The period of one cycle of 60 Hz alternating current is:

• A1.67 milliseconds
• B16.7 milliseconds
• C60 milliseconds
• D167 milliseconds

A 24-volt notification circuit draws 0.80 A. Round-trip copper resistance to the last appliance is 3.0 ohms. What voltage remains at that appliance?

• A21.6 V
• B22.4 V
• C23.2 V
• D24.0 V

Impedance (Z) differs from DC resistance (R) because impedance:

• AIncludes the frequency-dependent effects of inductance and capacitance as well as resista…
• BIs used only on Class 1 circuits
• CIs always smaller than the DC resistance of the same circuit
• DCannot be measured on audio or data cables

The New Mexico CID ES-3 examination and license classification are limited to special systems operating at:

• ANot more than 50 volts
• BNot more than 100 volts
• CNot more than 150 volts
• DNot more than 300 volts

NMAC 14.10.4, the New Mexico Electrical Code used on the ES-3 exam, adopts which National Electrical Code edition as amended?

• A2017 NEC
• B2020 NEC
• C2023 NEC
• DNFPA 72-2010 in place of the NEC

NMAC 14.10.4.16 amends NEC communications rules by requiring that any exterior wall penetration for communications circuits be installed:

• AWith only a drip loop and no raceway
• BIn a listed raceway
• CIn Schedule 40 PVC left open at both ends
• DThrough an unlisted plastic bushing larger than 2 inches

Under the NMAC 14.10.4 amendment to NEC 110.2, electrical wiring, equipment, or material approval is based on listing and labeling by:

• AAny importer’s CE mark
• BA nationally recognized testing laboratory recognized by OSHA
• CThe contractor’s in-house quality stamp
• DA city business-license decal

Why does the NEC treat a Class 2 circuit as providing acceptable electric-shock protection, while a Class 3 circuit requires additional safeguards?

• AClass 3 circuits are limited to 12 volts
• BClass 2 sources are power-limited so they are considered safe from fire initiation and pr…
• CClass 2 may share a raceway with 480-volt feeders without a barrier
• DClass 3 circuits are exempt from cable listing

Before starting ES-3 work that is subject to CID jurisdiction, NMAC 14.10.4.9 points the contractor to which administrative requirement?

• AElectrical permits and inspections as required by 14.5.2 NMAC and 14.5.3 NMAC
• BNo permit is ever required for circuits under 50 volts
• COnly a verbal notice to the serving utility
• DA federal FCC construction permit

A 70-volt distributed loudspeaker system is used primarily because it:

• AEliminates the need for an amplifier
• BLets many speakers be placed on a long run of relatively small cable by using matching tr…
• CRequires each speaker to be 70 ohms
• DIs the only wiring method permitted by NEC Article 640

A 70-volt amplifier is loaded with six speakers tapped at 4 W and two speakers tapped at 8 W. What is the total speaker load?

• A32 W
• B24 W
• C40 W
• D70 W

Four 8-ohm loudspeakers are paralleled on a low-impedance amplifier. What impedance does the amplifier see?

• A2 ohms
• B4 ohms
• C8 ohms
• D32 ohms

A balanced microphone line using a 3-pin XLR is preferred over an unbalanced RCA line on long runs because the balanced circuit:

• ARejects induced noise by sending equal-and-opposite signals that cancel at a differential…
• BCarries twice the phantom voltage on the shield
• CMay be installed in the same raceway as 480-volt feeders without 725.136 precautions
• DDoes not require a listed cable type

Which NEC article specifically covers audio signal processing, amplification, and reproduction equipment?

• AArticle 640
• BArticle 700
• CArticle 760
• DArticle 820

A 60 Hz hum appears only when a mixer, amplifier, and video display share multiple AC ground paths and shield connections. The most appropriate first correction is to:

• ALift the equipment grounding conductor on the amplifier power cord
• BBond the audio shields to a separate isolated ground rod
• CReplace all XLR cables with unshielded speaker wire
• DIdentify and break the unintended shield/ground loop, using isolation, a single-point shi…

Compared with a low-impedance (4/8-ohm) speaker system, a 70-volt constant-voltage system:

• ACannot use transformers at the speakers
• BMakes speaker count and tap wattage additive so long runs stay within voltage-drop limits…
• CRequires each home-run to be 70 ohms
• DIs limited by NEC to 10 feet

Which signal is the lowest nominal level and therefore the most sensitive to induced noise?

• AMicrophone level
• B70-volt distributed speaker level
• CSpeaker level
• DLine level

HDMI is best described as:

• AAn analog composite video connector using 75-ohm coax
• BA digital audiovisual interface that carries video, audio, and control on a single cable
• CA 70-volt loudspeaker connector
• DA 100-ohm balanced microphone standard