A homeowner wants to install a 240-volt electric water heater. According to electrical basics for builders in Michigan, what is the minimum wire size required for a 30-amp circuit?
Correct Answer
A) 10 AWG
For a 30-amp circuit, 10 AWG wire is the minimum required size according to electrical code requirements for residential construction.
Why This Is the Correct Answer
The NEC (adopted in Michigan for residential construction) specifies that 10 AWG copper conductor is the minimum wire gauge rated for 30-amp circuits. Wire gauge and ampacity are inversely related — larger AWG numbers mean thinner wire. 10 AWG is rated at 30 amps, making it the minimum compliant size.
Why the Other Options Are Wrong
Option B: 6 AWG
6 AWG wire is rated for 55 amps — it is more than sufficient for a 30-amp circuit but is oversized and more expensive than necessary. It exceeds the minimum requirement and is not the correct answer to what the minimum is.
Option C: 8 AWG
8 AWG wire is rated for 40 amps. While it could carry 30 amps, it is larger than the minimum required. The correct minimum is 10 AWG, not 8 AWG. Using 8 AWG when 10 AWG is sufficient adds unnecessary material cost.
Option D: 12 AWG
12 AWG wire is rated for only 20 amps. Using 12 AWG on a 30-amp circuit would be a code violation — the wire would be undersized relative to the breaker rating, creating a fire hazard since the breaker would not trip before the wire overheats.
Memory Technique
Use the '10-30' pairing: 10 AWG for 30 amps. Similarly remember '12-20' (12 AWG for 20 amps) and '8-40' (8 AWG for 40 amps). The pattern: subtract 10 from the AWG to get the amp rating roughly, or better — memorize the 10/20/30 → 10/12/14 AWG table as three anchor points.
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