Michigan Electrical Code and Low Voltage Scope
This domain tests whether you can place a low-voltage installation under the correct article of the Michigan Electrical Code (MEC) and whether you know who may perform the work. The MEC adopts NFPA 70 with Michigan amendments. Low voltage is a trade phrase, not a code classification; the code classifies circuits by article and by power limitation.
Core rules
- Article 725 covers Class 1, Class 2 and Class 3 remote-control and signal circuits. Class 1 is not power-limited and generally uses Chapter 3 wiring methods. Class 2 and Class 3 circuits must be supplied by a listed source and stay within the Chapter 9 Table 11(A) or 11(B) limits.
- Article 760 covers fire alarm, Article 770 optical fiber, Article 800 communications, Article 810 radio and TV, Article 820 CATV, and Article 830 network-powered broadband.
- A 24 V circuit is not automatically Class 2. The listing of the source and its VA or current limit decide the class.
- Article 90 scope excludes utility-owned equipment and certain other systems, but a circuit is not outside the MEC merely because it is low voltage. Licensing and permits are separate requirements.
Worked example
A listed 24 V AC, 40 VA transformer feeds a doorbell. Current is 40 VA divided by 24 V, or 1.67 A. The source is a listed Class 2 transformer and the current is within the Class 2 limit for that voltage, so Article 725 Part III applies to the wiring. Replacing it with a 24 V, 100 VA transformer would exceed the Class 2 power limit unless a listed current-limiting source were used.
Traps
Calling every circuit below 50 V Class 2; using Article 725 for fire alarm; letting a thermostat cable share a box with line voltage because it is low voltage; ignoring Michigan permit and licensing rules because the code article itself is permissive.