Minnesota Low Voltage Practice flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Ohm's law

Current equals voltage divided by resistance (I = E/R). Power equals voltage times current (P = E × I). In AC circuits, impedance Z replaces resistance R for reactive loads.

Three-phase power formula

For a balanced three-phase load, real power P = √3 × line voltage × line current × power factor. Single-phase power is E × I × PF.

Voltage drop formula

Single-phase two-wire voltage drop ≈ 2 × K × I × L ÷ circular mils, where K is about 12.9 for copper. NEC recommends total drop of 5% or less.

Series circuit

A circuit with only one path for current. Current is the same through every element, resistances add, and voltage divides in proportion to resistance.

Parallel circuit

A circuit with multiple current paths. Voltage is the same across each branch, conductances add, and total resistance is less than the smallest branch resistance.

Minnesota electrical licensing authority

The Minnesota Department of Labor and Industry administers electrical licensing under Minn. Stat. ch. 326B and Minn. R. ch. 3800, including exams, permits, and inspections.

Minnesota continuing education requirement

Master and journeyman electricians must complete 16 hours of continuing education per two-year renewal cycle, including required code-update hours.

Minnesota license classes

Minnesota issues master, journeyman, maintenance electrician, and registered unlicensed electrician credentials, each with a defined scope of work and supervision requirements.

Listed versus labeled

Listed means equipment has been evaluated by a nationally recognized testing laboratory. Labeled means it bears the listing mark. Approved means acceptable to the AHJ.

NEC Article 90 scope

Article 90 states that the NEC is a minimum safety standard, not a design manual. Chapters 1–4 apply generally; Chapters 5–7 modify or supplement.

Working space requirements

NEC 110.26 requires defined depth, width, and height of clear working space in front of electrical equipment, based on voltage and the condition of the location.

Box fill calculation

NEC 314.16 counts conductors, clamps, devices, and equipment grounding conductors, then applies Table 314.16(B) volume allowances to determine required box volume.

NM-B cable restrictions

Nonmetallic sheathed cable is permitted in dry locations only. It is prohibited in wet locations, where exposed to physical damage, and in most commercial occupancies.

EMT support spacing

Electrical metallic tubing must be supported within 3 ft of each box and at intervals not exceeding 10 ft, per NEC Article 358.

Firestop requirements

Cable and raceway penetrations of fire-rated assemblies must be sealed with a listed firestop system matching the tested assembly, restoring the assembly's fire rating.

Class 2 circuit definition

A circuit limited to 100 VA or less that is generally exempt from Chapter 3 wiring methods when installed per NEC Article 725.

Class 2 separation rule

Class 2 and 3 conductors must be separated from power conductors by at least 2 in. or a barrier, unless the cable is listed for the combined use.

Low-voltage lighting limit

NEC Article 411 covers lighting systems limited to 30 V and 25 A per circuit, supplied by a listed power source.

Grounding electrode resistance

NEC 250.53 requires a grounding electrode system resistance of 25 ohms or less. If greater, a second electrode must be installed.

Main bonding jumper

The main bonding jumper connects the equipment grounding conductor to the service neutral at the service equipment. It must be removed for separately derived systems.

Overcurrent device selection

Per NEC 240.4, the overcurrent device rating must not exceed the conductor ampacity, except where the next-size-up rule in 240.4(B) applies.

Fire alarm cable listings

Fire alarm cable must be listed FPL, FPLR, or FPLP. FPLP is required in plenums and air-handling spaces; FPLR is riser-rated.

Smoke detector spacing

NFPA 72 requires spot-type smoke detectors on smooth ceilings to be spaced no more than 30 ft apart, with adjustments for ceiling height and beam pockets.

Manual pull station location

NFPA 72 requires manual pull stations within 5 ft of each exit door, mounted 42–48 in. above the floor to the operating handle.

Communications cable listings

Communications cable must be listed CM, CMR, CMP, or CMX depending on location. CMP is required in plenums and air-handling spaces.

Primary protector requirement

Communications conductors entering a building and exposed to lightning or power contact must have a listed primary protector installed per NEC Article 800.

PoE installation considerations

Power over Ethernet installations must consider cable ampacity, bundling, and temperature. NEC Articles 725 and 800 apply to the low-voltage cabling.

Arc flash boundary

The arc flash boundary is the distance at which incident energy equals 1.2 cal/cm². Inside it, arc-rated PPE is required per NFPA 70E.

Hierarchy of risk control

NFPA 70E orders controls as elimination, substitution, engineering controls, awareness, administrative controls, and PPE as the last line of defense.

Lockout/tagout procedure

Before work on de-energized equipment, apply locks and tags, release stored energy, and verify absence of voltage with a tester rated for the circuit.

Panel schedule purpose

A panel schedule lists circuit numbers, breaker sizes, conductor sizes, and connected loads, and is used to verify load calculations and spare capacity.

As-built drawings

As-built drawings reflect field changes made during construction and are submitted before final inspection for future maintenance and code compliance.