Mechanical, Electrical, and Plumbing Systems
This domain tests rough-in coordination, code clearances, HVAC sizing, electrical circuits and grounding, and plumbing traps and venting. Questions often require applying NEC, IPC, or IMC rules to a simple field scenario.
Core rules and concepts
- HVAC systems are sized by load calculation, not by rule of thumb. Duct sizing and return air paths affect performance. Clearances to combustibles and access for service are code requirements.
- Electrical work follows the NEC as adopted in Nebraska. GFCI protection is required in bathrooms, kitchens, laundry areas, garages, outdoors, and other wet or damp locations. AFCI protection applies to many dwelling branch circuits.
- Wire ampacity and overcurrent protection must match. A 20-ampere circuit generally uses 12 AWG copper. Grounding and bonding must be continuous and properly terminated.
- Plumbing requires fixture traps with a 2-inch to 4-inch water seal, venting to protect the seal, and proper slope on drains. Water heaters need a TPR valve and discharge pipe.
Worked example
A bathroom receptacle is installed near a lavatory. The circuit is 20 amperes with 12 AWG copper. The receptacle must have GFCI protection because it serves a bathroom. A standard non-GFCI receptacle is a code violation even if the circuit is properly grounded. The reasoning is location-based, not based on the appliance.
Traps that cost marks
Sizing HVAC by square footage alone; omitting GFCI in required locations; mismatching wire and breaker; installing a trap without a vent; and failing to coordinate penetrations and firestopping.
Key point: location and load determine code requirements in MEP work.