The electrical and mechanical scope checklists on this site both flag this boundary from their own side, because it's the single most consistent source of missed scope on a Canadian ICI tender: the line between Division 23 (mechanical) and Division 26 (electrical) at every motor-driven piece of equipment on the job. This article goes a level deeper — into what's actually written on a real equipment schedule, why the assignment changes from unit to unit, and the check that closes the gap before the number leaves the office.
There's no code-mandated default here. The CEC requires a disconnect within sight of a motor; it says nothing about which contractor buys, mounts, or wires it. That decision gets made twice on every tender — once by the mechanical engineer writing the equipment schedule notes, once by the electrical engineer writing Division 26's general notes — and the two documents don't always agree, or even address the same equipment.
The five items actually in dispute
Starters
A motor starter is either furnished as part of the packaged mechanical equipment — built into a rooftop unit's own control panel — or supplied loose for field mounting in a motor control centre. The first case usually stays mechanical, start to finish. The second is where specs diverge: "furnished by Division 23, mounted and wired by Division 26" is common, but so is the reverse, with electrical furnishing, mounting and wiring everything past the breaker. Both patterns are legitimate. The schedule note — or its absence — is what decides which one applies to this unit.
VFDs
Variable frequency drives carry the same ambiguity as starters, plus a wrinkle: a VFD usually has two connections, not one — line power in, and a control or speed-command signal back to the building automation system. A spec can split those connections between trades even when it assigns the drive itself cleanly: Division 26 supplies and wires the VFD, but the low-voltage speed-command wiring back to the BAS is Division 23's controls contractor. Missing that second connection costs as much as missing the drive.
Disconnects
A local disconnect switch is required within sight of most motor-driven equipment, and "required" only tells you it has to exist — not who buys it. A disconnect that ships factory-mounted on packaged equipment is effectively mechanical's by default, though electrical still runs power to it and has to confirm whether it's fused to match the branch circuit protection. A field-installed disconnect is squarely a Division 26 item on most tenders — one of the few boundary items with something close to a real default.
Duct detectors
A duct-mounted smoke detector sits physically inside mechanical ductwork — someone has to cut the opening and mount the housing, a mechanical-trade task by nature — but it's electronically part of the fire alarm system, wired back to the fire alarm control panel by the fire alarm contractor. The device itself sometimes ships with the mechanical equipment and sometimes is furnished by the fire alarm sub for mechanical to install. Three possible owners for one small box, and the spec has to be read carefully to know which two actually apply here.
Damper and fan interlock wiring
Fire and smoke dampers are mechanical hardware, but their actuators need power and a control signal, and the interlock that closes a damper or shuts down a fan on a duct-detector or fire-alarm signal reads as either mechanical controls scope or electrical/fire-alarm scope depending on which spec note you're standing on. It's the item most likely to fall into the gap between two trades' "not us" assumptions, because neither side treats a few feet of interlock wire as real scope — until an inspector asks to see it work.
Why the same schedule splits it five different ways, unit by unit
The equipment schedule is written by the mechanical consultant; Division 26's general notes are written by the electrical consultant; a fire alarm sub-scope, where one exists, has its own notes again. Nothing forces the three documents to agree, and they're often drafted weeks apart, sometimes by different firms on a design-build team. The pattern that causes real trouble: a base-bid schedule of a dozen rooftop units, all wired the same way, then four exhaust fans added by addendum with the assignment flipped — because the addendum sketch came off a different desk than the base schedule, and nobody cross-checked the new units against the existing convention. Reading the first three rows and assuming the pattern holds for row thirty is exactly the assumption that fails.
The unit-by-unit check
This is the point both the electrical and mechanical checklists on this site make without room to expand on: check every scheduled unit individually, not the first few that seem to set a pattern. In practice, build a small matrix before pricing — one row per piece of equipment, one column each for starter, VFD, disconnect, duct detector, and interlock wiring — and for every cell, write down furnished-by and wired-by exactly as the spec states it for that unit, never inferred from the unit above it. Cross-reference three documents while you do it: the equipment schedule's own notes, Division 26's general notes (which sometimes make a blanket statement that overrides, or quietly contradicts, the schedule), and Division 28's fire alarm notes if the tender carries its own fire alarm sub-scope. A blank cell isn't a default in either direction — it's a gap, and it belongs on the RFI list before it goes into the bid.
What it costs when it's missed
The failure mode is rarely dramatic at bid time — it's a quiet gap that surfaces months later. A common version: a base-bid schedule of rooftop units carries VFDs furnished and wired by electrical; four exhaust fans added by addendum carry the opposite note, and the mechanical estimator, reading the addendum quickly against the pattern already priced, never re-checks the assignment. Nobody carries the four drives. Best case, it surfaces at submittal review — a resubmission, and a scramble to price four VFDs on short lead time. Worst case, it surfaces at startup, when the panel meant to house them is empty and the unit can't be commissioned. A missed duct-detector interlock is worse on timing — invisible until the fire alarm verification test, and a failed verification holds up occupancy, the kind of delay that shows up as liquidated damages, not just a change order.
A schedule worksheet
Five columns, checked against three documents, for every unit on the schedule:
| Item | Check per unit | Where to look |
|---|---|---|
| Motor starter | Furnished by / mounted by / wired by — three separate questions, not one | Equipment schedule note, Division 26 general notes |
| VFD | Line power connection and the separate speed-command connection to the BAS | Equipment schedule, Division 23 controls section, Division 26 |
| Disconnect | Factory-mounted (mechanical default) vs. field-installed (electrical default) — and fused or not | Equipment schedule, Division 26 |
| Duct detector | Who mounts the housing, who supplies the device, who wires it to the fire alarm panel | Mechanical ductwork details, fire alarm sub-scope, Division 26 |
| Damper/fan interlock | The physical actuator vs. the low-voltage interlock wire — different owners are common | Mechanical controls section, Division 26, fire alarm notes |
None of this is exotic reading. It's the equipment schedule, worked with the same unit-by-unit discipline as the panel schedule, cross-checked against two or three general-notes sections instead of trusted on its own — exactly the kind of check that a hundred-unit schedule makes tedious enough to skip, which is the whole reason it keeps costing money.