CSLB C-10 Electrical ContractorWiring Methods and MaterialsEasy
A homeowner asks why standard Type MC cable cannot be buried directly underground without additional protection. Which characteristic of standard MC cable explains this limitation?
- AMC cable lacks an equipment grounding conductor entirely
- BThe interlocked metal armor is not watertight or corrosion-resistant for direct burial
- CMC cable cannot carry more than 20 amperes
- DMC cable conductors are limited to 60°C insulation ratings
Show answer & explanationAnswer & explanation
Correct answer: B. The interlocked metal armor is not watertight or corrosion-resistant for direct burial
Standard Type MC cable has an interlocked metallic armor that is not sealed against moisture and is subject to corrosion, so it is unsuitable for direct burial or wet locations unless specifically listed and jacketed for that use.
Why the other options are wrong
- A. MC cable includes either a full-size internal EGC or relies on the armor/bonding strip, not a total absence of grounding.
- C. MC cable ampacity depends on conductor size, not a fixed 20A limit.
- D. MC cable is available with THHN/THWN 90°C rated conductors, not limited to 60°C.
MC Cable Limitations
Type MC (Metal-Clad) cable uses an interlocked or smooth metal armor; standard versions are not moisture-sealed and require listing for wet or underground use.
- Interlocked armor does not prevent water intrusion by design.
- Special jacketed/listed MC cable is required for wet locations or direct burial.
- MC cable is common in commercial branch circuits and feeders.
Memory trick: 'Metal armor loves air, hates water' — needs a jacket to go underground.