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Key Facts: MS T&D Lines Exam

70%

Passing Score

PSI MS Contractor Bulletin 4/23/2026

50 Q

Official Exam Questions

PSI MS Contractor Bulletin 4/23/2026

2 hours

Time Allowed

PSI MS Contractor Bulletin 4/23/2026

$120

PSI Exam Fee

PSI MS Contractor Bulletin 4/23/2026

Open book

Exam Format

PSI MS Contractor Bulletin 4/23/2026

MS Transmission/Distribution Lines PSI trade exam: 50 questions, 70% pass, 2 hours, fee $120. Open-book MSBOC classification (bulletin 4/23/2026).

Sample MS T&D Lines Practice Questions

Try these sample questions to review concepts for the MS T&D Lines exam. Each question includes a detailed explanation. Start the interactive quiz above for the full 100+ question experience with AI tutoring.

1A 25 kVA single-phase pole-mount transformer is fully loaded on a 240 V secondary. What is the approximate full-load secondary current?
A.10 A
B.52 A
C.104 A
D.208 A
Explanation: Single-phase current is I = S / V. Convert 25 kVA to 25,000 VA and divide by 240 V: 25,000 / 240 = 104 A. Line workers use this check when sizing secondary leads, connectors, and loading.
2What is the defining feature of a completely self-protected (CSP) overhead distribution transformer?
A.It has only a secondary winding and no primary winding
B.It includes internal overcurrent protection and typically a tank-mounted arrester so a separately mounted primary cutout is not required
C.It can be installed only on a concrete pad
D.It must be fused exclusively with a station-class circuit breaker
Explanation: A CSP transformer carries its own primary protective link, usually a secondary breaker, and a lightning arrester on or in the tank. That package replaces the external fused cutout and separately mounted arrester used with a conventional unit, which is why CSP units are common on simple overhead services.
3Compared with a pole-mount distribution transformer, a pad-mount transformer is typically selected when:
A.The primary is an overhead bare ACSR feeder and no underground cable exists
B.The installation is an underground residential or commercial service that needs a lockable, ground-level enclosure
C.The unit must be climbed for all switching
D.Only a single-bushing live-front tank is allowed in a public area
Explanation: Pad-mount transformers sit on a concrete pad at grade and serve underground cable systems. The lockable compartment keeps energized parts away from the public. Pole-mount tanks belong on overhead construction; pad-mounts belong on URD and similar underground feeds.
4The kVA rating on a distribution transformer nameplate is a rating of:
A.Apparent power the windings can carry continuously under the nameplate voltage and temperature rise
B.Real power in kilowatts that the transformer can deliver at unity power factor only
C.The utility's peak system load in megawatts
D.The interrupting rating of the primary fuse
Explanation: Transformer capacity is given in kilovolt-amperes because heating depends on current, not on the load power factor. A 25 kVA unit can deliver 25 kVA continuously at rated voltage and rise whether the load is mostly watts or a mix of watts and vars.
5Why is a wye-connected secondary preferred on a multi-grounded four-wire distribution system?
A.A wye connection provides a common neutral point that can be grounded and used for single-phase loads
B.A wye secondary has no neutral, which eliminates ground-fault current
C.A wye secondary can be used only with delta primaries and never with wye primaries
D.Wye secondaries block all lightning surge current
Explanation: In a wye, the three windings meet at a neutral. That point is grounded and carried out as the system neutral so single-phase transformers and services can be connected phase-to-neutral. A delta secondary has no inherent neutral and is a three-wire system unless a grounding transformer is added.
6A single-phase transformer is rated 7200 V primary and 240 V secondary. If the primary winding has 1,800 turns, how many secondary turns are required for the same volts-per-turn?
A.30 turns
B.60 turns
C.240 turns
D.1,800 turns
Explanation: Turns ratio equals voltage ratio: Vp / Vs = Np / Ns. 7,200 / 240 = 30, so Ns = Np / 30 = 1,800 / 30 = 60 turns. Ugly's and lineman references use this same ratio to check primary and secondary voltages before energizing.
7On a conventional (non-CSP) pole-mount transformer, the primary fused cutout is installed mainly to:
A.Protect the transformer and isolate a failed unit from the primary feeder
B.Regulate secondary voltage under load
C.Serve as the customer's main service disconnect
D.Bond the tank to the multi-grounded neutral
Explanation: A conventional transformer has no internal primary fuse, so an external expulsion cutout is hung on the pole. The fuse is coordinated with transformer kVA and primary voltage so a winding fault or severe overload blows the fuse and drops the tank off the feeder.
8Before paralleling two single-phase distribution transformers on the same secondary, a line crew must verify that the units have matching:
A.Paint color and manufacturer only
B.Primary fuse sizes only
C.Voltage ratings, polarity, and compatible percent impedance
D.Oil types, even if voltages differ
Explanation: Paralleled transformers share load only if they have the same voltage ratio and polarity and similar impedance. A polarity or tap mismatch circulates current between tanks; a large impedance mismatch dumps most of the load onto the lower-impedance unit.
9A no-load tap changer on a distribution transformer is intended to be operated:
A.While the transformer is energized and carrying full load
B.As a substitute for a line voltage regulator under varying load
C.Only after the transformer is deenergized, to select a different primary voltage tap
D.To reverse polarity for paralleling
Explanation: Distribution no-load taps change the primary turns to match the feeder voltage (for example 7,200 V versus 7,620 V). The handle is interlocked for deenergized operation. Live tap changing requires a load-tap changer, which ordinary pole-mount units do not have.
10Three 25 kVA single-phase transformers are banked wye-wye to serve a 480 Y / 277 V three-phase load. What is the approximate full-load secondary line current of the bank?
A.30 A
B.52 A
C.90 A
D.156 A
Explanation: Bank capacity is 3 × 25 kVA = 75 kVA. Three-phase current is I = S / (V × √3) = 75,000 / (480 × 1.732) ≈ 90 A. Each tank still sees its own 25 kVA, but the line conductors carry about 90 A.

About the MS T&D Lines Exam

Mississippi Transmission and Distribution Lines is an MSBOC specialty classification trade examination administered by PSI. Official scope is underground and overhead electrical transmission lines, including poles, guys, towers, street and outdoor lighting of all voltages, underground ducts, transformers, circuit breakers, capacitors, primary metering, and related equipment. The official open-book exam has 50 questions, a 70% passing standard, and 2 hours allowed. PSI fee is $120 per portion (Candidate Information Bulletin updated 4/23/2026). This English-language MCQ bank is a study aid for the official content outline; it is not an official PSI form, does not replace the required Law and Business Management exam, and is not a substitute for MSBOC application review or the official open-book examination.

Exam sponsor: PSI Services LLC (for Mississippi State Board of Contractors). The requirements and fees below concern the certification or admission exam, separate from our free practice resources.

Questions

50 questions

Time Limit

2 hours

Passing Score

70%

Exam / Certification Fees

$120

Exam sponsor website

Fees, eligibility, and exam policies can change. Confirm them with the exam sponsor before applying or paying.

Our practice resources: topics covered

We aim to reflect publicly available exam outlines and topic information in our study resources. Coverage, format, and difficulty may differ from the actual exam, and we cannot guarantee that every detail is accurate or current. Confirm exam requirements, fees, and policies with the official exam sponsor.

12%

Transformers

Pole-mount, pad-mount, and substation transformer application

10%

Electrical Knowledge

Basic electrical theory used on supply systems

10%

Conductors

Overhead and underground conductor selection and sag

14%

Overhead Lines

Overhead construction, clearances, and hardware

8%

Underground Lines

URD cable, ducts, and underground construction

16%

Equipment and Safety

OSHA 1926 and line-work safety

6%

Grounding Methods

NESC grounding of supply systems

8%

Service Drops and Laterals

Overhead drops and underground laterals

8%

Poles and Structures

Poles, towers, guys, and structures

8%

Electric Supply Stations

NESC supply-station rules

Preparing for the MS T&D Lines Exam

What You Need to Know

  • Passing score: 70%
  • Exam length: 50 questions
  • Time limit: 2 hours
  • Exam / certification fees: $120 Official sources

Using Our Practice Resources

  • Work through all 100 available questions
  • Review every answer and explanation
  • Track weak areas and revisit them
  • Use our AI tutor for tough concepts

MS T&D Lines: Suggested Study Strategy

1Study only the approved references listed for Transmission/Distribution Lines in the current PSI Mississippi Contractor bulletin (updated 4/23/2026): NESC 2017, NEC 2020, OSHA 29 CFR 1926, the Lineman's and Cableman's Handbook, and Ugly's Electrical References
2Practice open-book navigation of NESC parts for stations, overhead, underground, grounding, and work rules
3Keep NESC (utility supply systems) separate from NEC (premises wiring) — do not mix the two codes
4Confirm MSBOC classification scope and eligibility at msboc.us before scheduling with PSI
5All applicants must also pass Law and Business Management unless it is waived

Frequently Asked Questions

How many questions are on the MS Transmission/Distribution Lines exam?

The official PSI examination has 50 scored questions (plus possible unscored experimental items). Passing is 70% within 2 hours.

How much does the MS T&D Lines exam cost?

PSI lists $120 per examination portion (Candidate Information Bulletin updated 4/23/2026). MSBOC application fees are separate: $400 commercial or $50 residential. Additional classifications are $100 each.

Is the Mississippi contractor exam open book?

Yes. PSI administers MSBOC classification exams as open book. Only bulletin-listed approved references are allowed; temporary tabs such as Post-it notes are prohibited.

Do I still need the Law and Business Management exam?

Yes. MSBOC requires the Mississippi Law and Business Management exam (50 questions, 70%, 2 hours) of all applicants. Reciprocity may waive a trade exam in some cases but does not waive Law and Business.