Michigan Low Voltage Practice flashcards

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

Article 725 scope

Covers Class 1, Class 2, and Class 3 remote-control, signaling, and power-limited circuits that are not an integral part of a device or appliance. It sets wiring methods, power limits, and separation rules for these circuits.

Class 2 circuit limits

Table 725.121(A) caps Class 2 circuits at 100 VA and limits voltage based on the source; inherent limits apply to dry-cell and listed Class 2 transformers. The listed power source defines the class.

Article 720

Applies to circuits operating at less than 50 volts between conductors, such as low voltage lighting and control. It requires listed equipment and permits Class 2 wiring methods where the source is power-limited.

Article 800 vs 725

Article 800 governs communications circuits such as telephone, data, and CATV, while Article 725 governs Class 1, 2, and 3 control and signal circuits. The system function determines which article applies, not the voltage.

PLFA and NPLFA

Article 760 divides fire alarm circuits into power-limited (PLFA) and non-power-limited (NPLFA). PLFA cable must be listed for fire alarm use and separated from power conductors per 760.139; NPLFA uses Chapter 3 methods.

Michigan code adoption

Michigan adopts the NFPA 70 National Electrical Code through the Michigan Electrical Code, enforced by the Bureau of Construction Codes. Amendments are published in the Michigan Administrative Code and local agencies enforce them.

CMP cable rating

The P suffix means plenum-rated and is required for cable installed in ducts, plenums, or other air-handling spaces per 300.22(C). Non-plenum cable in those spaces violates the code and fails inspection.

Cable support interval

CL2, CL3, and communications cables are generally supported every 4.5 ft (1.4 m) and within 12 in. of boxes, unless the applicable article specifies otherwise. Sagging unsupported runs fail rough-in inspection.

Stud hole protection

Cable through bored holes in framing must be at least 1-1/4 in. from the nearest edge of the stud, or protected by a listed steel plate per 300.4. This prevents nails and screws from damaging the cable.

Class 2/3 separation

Class 2 and Class 3 conductors must be separated from power conductors by at least 2 in. (50 mm) or by a barrier, unless installed using a Chapter 3 wiring method per 725.139. This reduces induced noise and fault risk.

Plenum wiring rule

Cable in an air-handling plenum must be listed as plenum-rated (CMP, CL2P, or CL3P) and have low smoke and flame spread. This applies to ducts and spaces used for environmental air per 300.22(C).

Firestopping penetrations

Where low voltage cable penetrates a fire-rated wall, floor, or shaft, the opening must be sealed with a listed firestop system. The electrical code does not waive this; the building code and inspector enforce it.

Wet location cable

Cable installed outdoors in wet locations must be listed for wet locations, such as UF or cable with a W suffix. Indoor-rated CL2 cable is not permitted in wet locations and will fail inspection.

Single-point grounding

A grounded low voltage system bonds its grounded conductor to the equipment grounding conductor at the source only. Additional bonds create ground loops and parallel paths that can carry objectionable current.

Communications bonding conductor

Article 800, Part IV requires the communications bonding conductor to connect to the building grounding electrode system or the nearest accessible point of the power grounding system, sized per Table 800.156.

Equipment grounding conductor size

Table 250.122 sizes the equipment grounding conductor based on the rating of the overcurrent device protecting the circuit. For low voltage circuits, the applicable article may permit a reduced size.

Equipotential bonding purpose

Bonding metallic raceways, trays, and equipment to a common point reduces touch and step potential differences. It also limits arcing between metallic parts during faults or lightning events.

Grounding electrode conductor

The grounding electrode conductor connects the grounding electrode system to the service or source. For communications and low voltage systems, its size follows the applicable table based on the largest conductor served.

Ground loop cause

Ground loops occur when shielded cable or equipment is bonded at more than one point, creating a closed path. Current flowing in that path induces noise; single-point grounding of shields reduces it.

Solder-only bonding

Grounding and bonding connections must be made with listed connectors and must be mechanically secure. Solder-only connections are not permitted because they can fail under heat or vibration.

Class 3 circuit limits

Class 3 circuits are power-limited but may operate at higher voltage and power than Class 2, up to the limits in Table 725.121(B). They require separation from power conductors and listed cable such as CL3.

CATV shield grounding

Article 820 requires the coaxial cable shield to be grounded at the building entrance, typically to the grounding electrode system. This limits voltage surges on the shield and protects equipment.

Primary protector function

A listed primary protector limits surge voltage on communications conductors entering a building where exposure to lightning or power contact exists. It must be bonded to the grounding system.

Motor control tap rules

Article 430, Part VI governs motor control circuits. A Class 1 remote-control circuit tapped from a motor branch circuit must meet the tap rules in 430.72 for conductor size and protection.

Fire alarm separation

Power-limited fire alarm cable must be separated from power and Class 1 conductors by at least 2 in. or a barrier, unless listed for the purpose. This prevents fault energy from reaching the fire alarm circuit.

Access control cabling

Access control, CCTV, and intrusion detection systems typically use Class 2 or Class 3 circuits under Article 725. They require listed CL2 or CL3 cable and listed enclosures for splices and terminations.

Class 1 circuit wiring

Class 1 circuits use Chapter 3 wiring methods and may share raceways with power conductors where the circuit is supplied by a power source and conductors are listed for the voltage. They are not power-limited.

Permit requirement

Electrical work in Michigan requires a permit from the local enforcing agency unless exempt under the Michigan Electrical Code. New circuits and alterations need permits; the permit must be available on site.

Contractor licensing

Electrical contractors must be licensed by the Michigan Department of Licensing and Regulatory Affairs (LARA). Journeyman and master electricians are licensed by examination and renew with continuing education.

Rough-in and final

The rough-in inspection occurs after wiring is installed but before it is covered. The final inspection occurs after completion; the enforcing agency must be notified when work is ready.

Plan review threshold

Commercial and multi-family projects may require plan review before a permit is issued. The local enforcing agency sets the threshold and reviews drawings for code compliance before construction begins.

Stop-work authority

The enforcing agency may issue a stop-work order for work without a permit or work not conforming to the code. It may order disconnection and require correction before work resumes.