Mechanical, Electrical, and Plumbing Coordination
Domain 8 - Mechanical, Electrical, and Plumbing Coordination
This domain tests whether you can plan MEP systems before the framing is closed, so that clearances, slopes, venting, and structural limits work together. Coordination failures show up as rerouted drains, blocked panels, and failed inspections.
Key coordination rules
- Electrical - keep a clear working space at panels: 30 inches wide, 36 inches deep, and 6.5 feet high. Protect cable from nails with plates where it passes through framing, use GFCI protection in kitchens, baths, garages, outdoors, and other wet locations, and AFCI protection where required. Bond metal piping and equipment.
- Plumbing - drain lines need fall: 1/4 inch per foot for 2-inch and smaller, 1/8 inch per foot for 3-inch and larger. Each fixture needs a trap and a vent; trap arms have length limits. Water heaters need a T&P relief valve piped to a safe drain and an expansion tank on a closed system. Avoid cutting structural members for pipes.
- HVAC - size equipment with a load calculation, not rules of thumb; provide return air, combustion air, condensate drainage, and clearance from combustibles. Protect refrigerant lines and seal ducts.
- Fire and life safety - firestop rated penetrations, maintain smoke and CO alarm coverage, and keep shutoffs accessible.
Worked example
A 3-inch building drain is planned through a 2x10 floor joist at midspan. The drain needs 1/8 inch per foot, but the joist cannot be notched or drilled to that size at midspan. The coordinator should lower the drain into a soffit, run it in a wall, or use an engineered penetration - not cut the joist. The same review should catch the electrical panel clearance and the water heater relief line.
Traps
Putting a panel in a closet without working clearance; running a drain with too little slope; forgetting the T&P discharge pipe; moving a fixture without upgrading the vent; undersizing return air; and failing to firestop.