Mechanical and Electrical Systems
Core concepts
This domain tests coordination as much as theory. For mechanical, know airflow (CFM), duct sizing, static pressure, equipment clearances, condensate management, and refrigerant and combustion-air requirements. For electrical, know voltage, current, resistance (Ohm's law), ampacity, conductor sizing, overcurrent protection, grounding and bonding, and clear working space in front of panels.
Coordination questions often hinge on sequencing: sleeves and blockouts before the pour, hangers and supports before ceilings close, and equipment set before walls. Also know disconnect locations, GFCI protection in wet areas, and that penetrations through fire-rated assemblies require listed firestopping.
Traps to watch
- Sizing a conductor by load alone while ignoring derating for temperature and conduit fill.
- Forgetting that a disconnect must be within sight of the equipment it serves.
- Blocking a panel's working clearance with stored material or ductwork.
- Running duct or pipe through a rated wall without an approved firestop.
- Ignoring condensate drainage slope and secondary containment where required.
Rule of thumb
Before any wall or slab closes, walk the route: is there a sleeve, a hanger, a disconnect, a clearance, and a firestop? If any is missing, stop the closure.
Worked example
A panel is installed in a corridor and a duct is routed 24 inches in front of it. Even if the electrician can reach the breakers, the required working space is obstructed. Resolution: reroute the duct or relocate the panel - the clearance is a code requirement, not a convenience.