Mastering MEP (Mechanical, Electrical, and Plumbing) Systems

A: 350 mg/L chloride is the trip point that burns you here. Above roughly 250 mg/L, copper sees accelerated pitting in oxidizing cooling water, and galvanized coatings dissolve fast at this TDS. 304 stainless looks attractive until you remember stagnant chlorinated water plus chlorides equals crevice attack at flanges and supports. Carbon steel with a barrier lining accepts uniform corrosion risk and controls oxygen pitting during layup.

A: The √3 term and both modifiers matter. 90,000 W divided by (1.732×480×0.88×0.92) lands near 135 A. Dropping efficiency or folding it into the kW rating is a common slip, and using kW/pf alone overstates kVA and pushes you toward nuisance breaker trips.

A: Minimum evaporator flow is the hard boundary. Once you cross it, the compressor sees unstable operation regardless of setpoint games. A controlled bypass or speed clamp preserves tube velocity and NPSH margin while letting coils ride their valves. The other moves either worsen part‑load instability or kill availability.

A: 35 kA at 480 V is already in the danger zone. Adding a VFD can change upstream breaker curves and arc duration, which directly drives incident energy. The code pushes a reassessment because time, not just fault magnitude, sets the burn severity your technicians face.