During a rough electrical inspection in Michigan, you notice THWN-2 copper conductors are being used for a 20-amp branch circuit. What is the minimum wire gauge required?
Correct Answer
B) 12 AWG
For 20-amp branch circuits, Michigan follows NEC requirements mandating minimum 12 AWG copper conductors. 14 AWG is limited to 15-amp circuits.
Why This Is the Correct Answer
NEC Table 310.12 (adopted in Michigan) specifies that copper conductors for 20-amp branch circuits must be a minimum of 12 AWG. THWN-2 at 12 AWG has an ampacity of 20 amps at 60°C (and higher at 75°C), which matches the circuit rating. This is one of the most fundamental NEC rules: 15-amp circuits use 14 AWG minimum; 20-amp circuits use 12 AWG minimum.
Why the Other Options Are Wrong
Option A: 8 AWG
8 AWG is much larger than needed for a 20-amp circuit. While 8 AWG copper is rated for 40-50 amps, using it for a 20-amp circuit is wasteful and unnecessary. This answer reflects an over-specification error.
Option C: 14 AWG
14 AWG is the minimum for 15-amp circuits, not 20-amp circuits. Using 14 AWG on a 20-amp circuit is a code violation because the wire is rated below the circuit breaker ampacity. If the breaker allows 20 amps, the conductor must handle at least 20 amps — 14 AWG is only rated for 15 amps.
Option D: 10 AWG
10 AWG is rated for 30-amp circuits and is larger than necessary for a 20-amp branch circuit. While technically safe (over-sized conductors are generally acceptable), 10 AWG is not the minimum required for 20 amps and represents unnecessary cost and material.
Memory Technique
The '15/14 and 20/12' rule: 15-amp circuits = 14 AWG minimum; 20-amp circuits = 12 AWG minimum. Notice the pattern: circuit amperage and wire gauge are inversely related (higher amps = lower AWG number = thicker wire). Memorize this pair: '20 amps → 12 gauge.'
More Michigan Questions
A residential foundation wall in Michigan is 8 feet high with 2 feet above grade. The backfill exerts lateral pressure of 30 psf per foot of depth. What is the maximum lateral pressure at the bottom of the foundation wall?
A builder discovers that the electrical service entrance was installed without proper permits. According to Michigan law, what is the most appropriate next step?
What is the maximum allowable span for a 2x8 floor joist (Grade 2 Douglas Fir) at 16" O.C. with 40 psf live load and 10 psf dead load according to Michigan Building Code span tables?
According to Michigan Building Code, what is the maximum height of a wood-framed bearing wall using 2x4 studs with standard construction?
A homeowner requests to convert a bedroom into a bathroom on the second floor. What is the primary Michigan code concern the builder must address?
According to Michigan plumbing regulations, what is the minimum pipe size required for a water service line serving a single-family residence?
A contractor is building a basement foundation wall that is 8 feet high and will retain 6 feet of soil. What is the minimum wall thickness required by the Michigan Building Code for poured concrete?
A homeowner wants to install a gas fireplace in their living room. The contractor notices the existing gas line is 1/2 inch black iron pipe. For a 40,000 BTU fireplace with a 25-foot run, is this pipe size adequate according to Michigan gas code?
During a framing inspection, the building official notes that the contractor used 2x4 studs at 24 inches on center for an exterior wall. According to Michigan Building Code, what is the maximum wall height allowed for this configuration?
A contractor is installing a beam to support floor joists. The beam must carry a total load of 8,000 pounds over a 12-foot span. If the allowable fiber stress for the lumber grade is 1,200 psi, what is the minimum required section modulus?
People Also Study
Business & Financial Management
120 questions · 70% to pass
Contract Administration
60 questions · 70% to pass
Project Management
60 questions · 70% to pass
Related Study Resources
Previous Question
You discover that a subcontractor installed plumbing rough-in without proper permits. As the general contractor in Michigan, what is your primary responsibility?
Next Question
In a residential kitchen renovation, what is the minimum number of 20-amp small appliance circuits required by electrical code standards adopted in Michigan?