Mechanical-electrical coordination checklist

Why this seam causes so many RFIs

Mechanical and electrical drawings are usually produced by different people, on different schedules, from different information. The mechanical engineer selects equipment and schedules its electrical data. The electrical engineer circuits it, often from an earlier version of that schedule. When the equipment changes, a substitution, a bigger unit, a different voltage, the electrical drawings have to change with it, and nothing forces them to.

The result is one of the most common sources of RFIs and field changes on MEP work: a breaker that does not match the unit it feeds, a disconnect nobody drew, a fan that must run in a fire but is fed from normal power. This checklist covers the checks that catch those errors before a set is issued.

Download the one-page checklist (PDF) Every check below on a single printable sheet, with space to list the units that changed this issue.

1. Equipment electrical data

Start with the equipment schedules, because every other check depends on them being right.

• Every scheduled unit has electrical data. Voltage, phase and either full load amps or MCA and MOCP, as the equipment type requires. A blank cell is an error, not a detail to finish later.
• The conductor is sized for the MCA. For air-conditioning and refrigeration equipment, the minimum circuit ampacity sets the minimum conductor size (NEC Article 440).
• The breaker does not exceed the MOCP. The maximum overcurrent protection on the equipment schedule is a ceiling. A breaker above it violates the listing; one below the MCA will trip.
• Voltage and phase match the panel. A 208 V three-phase unit on a 277/480 V panel, or a single-phase unit scheduled as three-phase, is caught here or in the field.
• Both disciplines show the same numbers. Compare the mechanical schedule and the electrical schedule side by side for every unit, not only the ones that changed.

2. Motors, drives and starters

• Someone owns every starter and drive. A responsibility matrix should say who furnishes, installs and wires each motor controller, variable frequency drive and disconnect. Gaps and double scopes both become change orders.
• Drives are located and powered. Each VFD appears on a plan with its location, working clearance and circuit, and the drawings agree on whether it is unit-mounted or remote.
• Motor circuits follow motor rules. Motor branch circuits, overload protection and controller ratings follow NEC Article 430, which sizes them differently from general-purpose circuits.
• Bypass and control wiring are defined for drives that need them, so the installer knows what is expected.

3. Disconnects and working space

• A disconnect is shown for every unit that needs one, within sight of the equipment as the NEC requires for motors and air-conditioning equipment, unless the unit carries a listed integral disconnect.
• Working space is clear. Disconnects, starters and panels in mechanical rooms and on roofs keep the required working clearance in front of them (NEC Section 110.26), and ducts and pipes are not drawn through it.
• Nothing foreign runs over the electrical equipment. Check that ductwork and piping are not routed through the dedicated space above panels and switchboards, a common clash in shared mechanical and electrical rooms.
• A service receptacle is near the equipment. Rooftop and attic HVAC equipment needs a service receptacle within reach, which the NEC sets at 25 feet (NEC Section 210.63).

4. Controls power

• Every controls panel has a circuit. Building automation panels, controllers and gateways often appear only on the controls drawings. Check each one has power on the electrical plans.
• Powered dampers and actuators are fed. Motorized dampers, smoke dampers and valve actuators that need line voltage are circuited, not assumed to be handled by the controls contractor.
• The scope line is written. The drawings say who provides power to controls devices and who provides the low-voltage wiring, so neither contractor prices it out.

5. Life safety interfaces

• Fans that must run in a fire are on the right source. Smoke control and stair pressurization fans, and any equipment the code or the smoke control design requires to operate in an emergency, are fed from the required emergency or standby source.
• Air handlers shut down on smoke where required. Duct smoke detection and fire alarm shutdown are shown for the air handlers the mechanical code requires them on, and the fire alarm drawings include the same devices.
• Fire and smoke dampers are monitored and powered where the design requires, and the damper schedule, the mechanical plans and the fire alarm drawings list the same dampers.

6. Heat and space in electrical rooms

• Electrical rooms are ventilated or cooled. Transformers, drives and switchgear give off heat. Check the mechanical drawings serve every electrical room and that the capacity reflects the equipment in it.
• Room sizes still work. When mechanical equipment grows, so do its electrical gear and clearances. Confirm the rooms still fit the equipment, the working space and a path to replace it.

7. After every substitution or revision

• Re-run the electrical data check for any unit that changed make, model, size or voltage, even if the change looks mechanical only.
• Update both schedules in the same issue. A revision that clouds the mechanical schedule and not the electrical one tells the contractor only half the story.
• Keep a list of units that changed between issues, so the coordination check starts from what moved rather than from the whole set.

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